KyleStubbins.com

Picture of kick panel? What picture? What is a kick panel?

OK....I just lost my 4WD trying to get over the snow in front of me in my parking space at work this morning. I got stuck bad four times in the last 1/2 mile before home and finally had to walk the last 1/8 mile. It took me two hours to get home (about 5 miles!!!). Maybe they should have plowed the roads??? My one son in law thinks I may have tried it in reverse. He has a Ford that won't allow 4WD in reverse. Is Chevy the same way? I remember having it in 4HI then trying 4LO but at one point both lights were blinking now they don't light at all. I just used 4HI a few days ago but never tried 4LO until today. I read all the reviews about American vehicles and like a fool I bought this Blazer because it seemed like a good deal. I'm still trying to figure out some of the electrical problems out. Our great car companies thought they were going to sell junk forever and we were going to keep buying it. WRONG!!!! This is my last American car until something changes. Just this week I junked my Pontiac with the famous Quad4 engine that broke a connecting rod twice.. A couple years ago I scrapped my Dodge Caravan after the trans mission EXPLODED twice. And I do mean explode! NO MORE GM, Ford, Chrysler!!!

Kyle's reply: Hi there! Yeah, I did forget about taking some more pics -- for whatever reason (probably the lack of light), the pics I took were very fuzzy. I'll have to try and remember to take some more.

I can describe it a little more for you though! The "kick panel" is located on the passengers side, front seat, right where the passengers right foot would rest. If you're sitting in the passengers seat, "swing" your right foot from left to right while keeping your heel on the floor. When your toes hit something on the right... you have found the kick panel! :) This panel is snapped on, but it does hook under a couple of other plastic panels, so be a little careful with it.

Once you have removed the plastic kick panel, you will see a "silver box", approximately 4" x 6", with a large electrical plug into the side (about 30 wires) -- that is your 4x4 control module. What you're looking for is a whitish-greenish "powder" on the electrical contacts -- that is corrosion and causes loss of signal from the 4x4 module. I had two wires (#2 and #6, if I remember correctly) that were actually broken due to the corrosion.

Like I said, I will try to remember to get some more pics -- hopefully this will help you find your module though!

Regards;
Kyle

my issue is I can not dis-engage 4x4 in my 95 four door Blazer.
It is stuck in low.
I tried running in reverse ( worked for my friends 95 Blazer)
disconnected battery ( figured it might be electrical)
I need to know is this module you describe in the floor?
Or below the glovebox?

the reverse 'seemed' to work but the engine revs up to 2000 rpm and does not go very quickly. When I do get to 25 mph it drops into 4x4 AGAIN!
Argggg.. Could it be the cold? It has been below freezing for two weeks now and to compound the issue I have no heat either in the vehicle.
Any help appreciated as I need vehicle to work.

Kyle's reply: Hi Spencer;

I still don't have pics yet, I've just been busy with a ton of stuff right now -- but I can go over a few things for you to check/do.

I'm not 100% on the 1995 model year, whether the controls are in dash or what (I know they are on 98-05). My in dash control has 2, 4HI then 4LO, each with their own light to indicate which mode is engaged. When you engage 4 LO, if you are not in neutral (or reverse, but under 5MPH), the 4HI and 4LO lights should flash and then 4HI will kick in instead of 4LO -- this is what I think may be happening to you and why 4 wheel drive is kicking in at 25MPH (4HI will kick in at much higher speeds than 4LO). This may indicate a module wiring problem, it's hard to really say, but a good place to look.

OK, the module location -- I can't really describe it better than I did for the last comment poster, but in case you missed that part... sit in the passenger seat -- swing your right foot back and forth while keeping your heel on the floor -- you'll hit your left foot one way, and the plastic panel where the module is located the other way. Some older pickup trucks had a "vent" pull handle located there, if that helps!

As for the cold causing the problem -- could be. That's the problem -- there are so many things it could be.

There is, what is called an "encoder module", on the side of the transfer case that controls which mode you are in (2, 4HI, 4LO) -- if water got in there and froze, it could be preventing the encoder from changing modes. The encoder motor could also be bad. Anyway, if worse comes to worst, you can unscrew the encoder module and manually shift the transfer case into any mode you wish. Unfortunately, I can't tell you which way is which -- you'll have to figure that out with trial and error! Don't worry, you can't hurt anything -- you'll either be in 2 wheel drive, or one of the 4 wheel ranges. If it's not 2 wheel, try again until it is! (There will be metal "tab", for lack of better words to describe it, sticking out of the transfer case -- put a wrench on it and it should move with minimal effort. NEVER FORCE ANYTHING! Take it for a drive and see what you're in. Hopefully, you'll get it on the first try!

Without knowing what is going on with your controls, I don't know what more I can offer. If your controls work, and you here the Transfer Case Control Module (TCCM - the module under the passengers kick panel!) "click-click", then it's working -- have someone do that while you listen under the vehicle for the encoder motor. If you hear that, then you have issues further along the system, such as the servo or actuator (vacuum operated, located under the battery).

You could also unplug the TCCM and tap on the encoder module to see if it may just be stuck (a warm garage wouldn't hurt either!) -- leave the TCCM unplugged for at least 2 minutes, then plug it back in. Then, turn the key on to off 5 times, then to on and try it.

You may also look for a friend, or mechanic, that can read your DTC's (Diagnostic Trouble Codes). They are extremely helpful!

Hopefully, this will give you something to start with. Let me know how you make out, or if I can answer any other questions.

Good luck!

Regards;
Kyle

I have a 2000 blazer, and had the same problem as you described. I took the kick panel off, tightened up the wires, and it worked!! Thanks so much for the insight and guide.

Kyle's reply: Hi Timothy!

That's awesome! I'm glad that my experience was able to help you -- that's why I post them! ;)

If you noticed any signs of corrosion, I would strongly recommend unplugging the module and applying some "dielectric gel" to the plug and then reconnecting it. Every module that I have looked at shows signs of moisture/condensation -- a definite weak point that some dielectric gel will take care of. You can get it at most auto stores -- Canadian Tire, PartSource, etc in Canada -- Pep Boys, AutoZone, etc. in the US.

Regards;
Kyle

On my 2003 Chev S-10 with 6cyl automatic, I had to have the 4WD control module replaced once because I couldn't make it shift into 4WD. Now about a year and a half later I am having the same problem. I have located the unit in the passenger area next to the front door, and here are all of the numbers which are printed on the unit: 25784 11:03-03
15741322
TV8N0723339808 . My problem here is that I cannot locate a replacement module anywhere, not at autozone.com, partsamerica.com, napaautoparts.com or even acdelco.com . Nobody is listing a module relating to four wheel drive or transfer case. If anyone can help with a supplier of this part, please email me at WeinCellar1811@aol.com . Thankyou, Dale

Kyle's reply; Hi Dale;

First, the module is actually called a "TCCM" (Transfer Case Control Module) -- that should help searching for one.

Keep your eyes on eBay -- I just saw one go for $135 that a guy bought brand new 6 months ago and is scrapping the truck. You can find them at the Chevy dealer, but they are right around the $500 mark -- ouch!

I am going to assume that you have read my post above and have looked at the connector and wires...

The only other thing that I can suggest is a "home repair". Obviously, I do not know what kind of problem you are having, but let's assume that you have dash lights and the light DOES go to the 4x4 high (or low) position -- at this point, listen to see whether or not you hear a definitive "click-click" coming from the TCCM. If you DO NOT hear the "click-click", you have a bad relay in the TCCM. The good news -- you can get a replacement relay at your local electronics store and replace it in the TCCM. You will need a soldering iron and some basic electronics skills, but it is very easily achieved (a couple of points to unsolder and then resolder the new relay in place).

Now, if you DO hear the "click-click", then your TCCM is working and trying to shift into 4WD -- the problem, IMO, would then be with the module that is actually on the transfer case (I forget the term for it right now) -- it is a simple "motor" setup that simply moves the transfer case gears to the proper mode.

Heck, if ya want to "hack" it together, you could always remove the module from the side of the transfer case, cut a hole through the floor and put an actual shifter through the floor and attach it to the pin on the transfer case (I wouldn't recommend this on an '03... maybe leave that trick for one that is falling apart and you don't want to spend another dime on it!) -- then you can shift into 4WD manually (AGAIN... NOT RECOMMENDED on a street vehicle!!).

Hope I've helped! If there is anything else I can do, feel free to ask away!

Regards;
Kyle

Okay so I got the kick panel off.. and yup, being i sunk half my truck lol, it is indeed corroded. I got the box off the frame but now i cant seem to get the main plug off the box its self. the Orange plug wont Unplug. and all those little wires they are supposed to connected right?.. i actually see one wire completely out of the main plug. cant see where it belongs tho because i cant get the plug off. Idk any help would be great.. and those pictures you said you were going to take would be awesome.. Thanks.. Jay

Ok So scratch that last comment. Now im Stuck in a different spot. got the module off and all is fine. my problem here now lies in the plug. there are 2 wires disconnected. And i cant figure out what spot they unplugged from.

Kyle's reply; Hi Jay;

I will go out and take pics before I leave for work this morning or I will forget again. I will try to get a good shot of the connector to help you locate where the wires go. No being smart here, but you *should* be able to see where they go... because there will be a hole where the wire should go. The only problem you will have is because you have two wires disconnected, you will need to know which one goes to which hole (terminal).

If you tell me the colors, I can try and locate them for you (be specific with wire colors -- ie. white with light green stripe, pink with dark blue stripe, etc.).

Regards;
Kyle

UPDATE - images have been added to the main article

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diagram of fuse # 3 cruise control needed and any feed back on
that fuse popping. also controls voltage for back lighting and
gauges.

Kyle's reply; Hello Guest;

Here's a good place to start --> 2000 Blazer S-Series Cruise Control Wiring.

Regards;
Kyle

I have no vacuum at actuator under the battery. When I put car into 4 hi I can hear something center hood "running" for several seconds. Does this indicate the tccm is ok?, The vac hoses run under what would looks like a distributor cap. This seems to be where the running motor noise comes from, but I can,t reach under there far enough to check for breaks in the vac lines. Can I safely start dissembling the ignition system to get at lines?

Since October is prime fishing time on NC Outer Banks and 4wd is a must, can I manually put vehicle in 4 hi by pulling the cable that goes into actuator? for a temporary fix. Back diff seems to lock but is hard to tell around here, too flat and too dry.

Thanks, John

Kyle's reply;

Hi John;

My first question would be, what are the lights on the dash doing (the 4wd pushbuttons)? And second, what year of vehicle are we talking? (I'm also assuming we're still talking about a Chevy Blazer.)

What you describe sounds like the ported vacuum switch (NOTE: this switch is only on 1999 and up vehicles). I'm not sure on the "hearing something running" -- what does it sound like? The vacuum switch shouldn't make much noise, not enough to be confused with something running. What I suspect is you are hearing the encoder motor on the transfer case trying to shift it into 4wd.

The drivers side, front axle is always engaged with the front diff -- the passengers side, front axle is controlled by the vacuum switch, actuator and cable. The vacuum switch is a common component to fail.

There are two problems trying to get your vehicle into 4wd with a failed vacuum switch;

1) you can pull on the cable to engage the passengers side hub -- but it will disengage when you release it as vacuum normally holds the diaphram closed, which holds the cable, which keeps the hub engaged.

2) the vacuum switch also communicates with the TCCM -- no vacuum and your lights will probably flash continually while trying to engage 4wd, but won't engage until all 4wd components, once again, communicate with each other.

You can test the vacuum switch (of course, once you get to it) by removing the two hoses from the switch and connecting them together -- if the cable moves to engage the passengers side hub, the vacuum switch is bad. If you really don't want to replace the switch, you can get a female/female hose adapter and join those hoses together (front hub will ALWAYS lock after doing this). Unfortunately, getting to the vacuum switch can be a problem, as you have found. I don't want to say "yeah, start ripping stuff apart" as I cannot really answer that question -- only you will know if you have the capability to disassemble things and be able to put them back together. If you feel you can remove a distributor cap, etc. and put them back after, go for it! You'll save yourself a ton of $$$ doing it yourself.

Oh, as a start, the vacuum comes off the drivers side manifold and goes to a reservoir (also on the drivers side), then to the vacuum switch (center firewall), then to the actuator (under the battery).

Well, I'm heading off to work, so I hope this helps -- if I think of anything else, I will post it here. If you have further questions, feel free!

Regards;
Kyle

PS - here's what you're looking for (the vacuum switch, located on the firewall)

Click the image for a full size view

Kyle:

I had the same problem on my 2000 sonoma. The dash lights on the 4WD switched did not light up.

I punched in the part number on Google and found your site.

You called it right - pins 1 and 6 wires corroded and broken. I couldnt get the terminals on time, so I cleaned out the connector, also cleaned the pins, stripped off some fresh wire. Then, I put the harness back together, leaving out 1 and 6. I then inserted the newly stripped wire from the back side of the connector, then packed in aluminum foil down into channel 1 and 6. Works great.

Thanks for posting - repairs like this save lots of time and money - total time to repair about 1 hour. Research time - about three.

Have agood one - Pablo.

Kyle's reply;

Hi Pablo -- I'm glad that I was able to help you solve your 4WD problem!

An interesting repair -- way to use your head!

Regards;
Kyle

Hey Kyle,
Same thing as Pablo above. Your blog helped me so much I cant thank you enough. Just a little tip, I couldn't find any terminals at the electronics stores that would fit this connector, so I rigged some computer terminal wires and they fit just fine, no glue needed either. You saved me a "bunch of money" and I didn't even have to switch to Geico.
Thanks.

Kyle's reply;

Awesome! I'm glad I was able to help solve your problem. :)

Kyle

Kyle....any idea where i could get my hands on a schematic for the vacuum system for the 2003 Blazer? I have a heater issue that i believe is tied to the vacuum system. After the truck is warmed up, under 40mph, the heater blows cool air, then at highway speeds it's hotter than blazes! any thoughts?

Kyle's reply;

Hey Jay;

No, I don't have anything AFAIK -- but I do have a buddy that has the All-Data system and may have it (he printed out some great schematics for my TCCM yesterday) -- I'll ask him today and if so I will post it here for you.

As for your problem -- I have noticed that as well -- not to the extreme that you state, but I have noticed that the Blazer runs cool when at idle and/or low speeds -- on the highway you're melting your eyebrows!

I've meant to look at the heating system since like last winter -- just never seem to get around to it (maybe 'cause I don't use it in the summer... WHEN I feel like fixing it!). I have a definite "vacuum" noise coming from under the dash, near the heater core. At low speeds it "whistles" (like a leaking vacuum would sound like), and goes away at higher speeds.

So, I will try to find a schematic for you, and hopefully you can help ME solve the same problem! :)

Kyle

I have a 1999 Blazer LT that I am trying to get to engage in auto 4X4 or 4hi. When I press either button the lights blink as though it wants to go into 4 wheel drive but then it goes right back to 2hi. Can you tell me what my problem is and if it is an easy repair? I hear no noise while I am pushing the button, just the lights blink and then return to 2hi. Can anyone help me?

Kyle's reply;

Hi Alice;

What you have is a breakdown in the system. Yeah, I know that sounds pretty obvious -- what you have in a 4WD system is multiple components that talk to each other (electronically) -- if one on the components doesn't respond the system doesn't know what to do and, basically, will do nothing. To put it into terms that may be easier to understand...

You have a cordless phone -- you pick it up and press the talk button to get a dial tone, but you don't get a dial tone -- instead, you get a series of beeps after a few seconds. What is happening is, you press the button on the phone (buttons on your dash) -- a signal is sent from the phone to the base unit (Transfer Case Control Module) -- the base unit is not plugged in, so it does not respond to the signal from the phone -- the phone doesn't know what to do, so it beeps at you to say there is an error. This is, basically, how your 4WD system works.

Anyway, it could be a few things;

1) let's start off with the easy things -- have you checked your fuses? Don't assume that just because the fuses are labeled 4WD that they are the only ones for your 4WD system! Fuse 10 (on my 2003 Blazer) is for the courtesy lights -- but guess what? It also controls the logic side of the TCCM (+5VDC). Pin 6 (thinner orange wire) should produce +5VDC and should be HOT AT ALL TIMES (meaning you should be able to read +5VDC on the line anytime, key on or off). The two large orange wires are your +12VDC lines and are controlled from the 10A fuse located in spot #15. I would check your LARGE orange wires as you are getting +5VDC logic as the lights are coming on on the dash. The +12VDC is used for the encoder motor -- check to make sure you have +12VDC at both the large orange wires (they are right beside each other... and there are two large black wires beside them that are ground).

Notes: All black wires are ground -- all orange wires are power (hot). There is a 10A fuse (#15) for the 4WD system, located in the fuse panel. There is a 20A fuse, located under the hood, that is also for the 4WD system (I'll have to look up the fuse number). The 4WD system also pulls from the 10A courtesy lamp fuse (#10).

2) the vacuum switch (located on the firewall -- see one of my posts above for a picture) or vacuum diaphram (located under the battery) could be malfunctioning. The job of these components is to pull on a cable which engages the front, right 4WD hub. I don't think this is likely to be your problem as you should probably hear the encoder motor running (changing the drive mode from 2Hi to 4Hi/4Lo) -- but there is a sensor on the hub to tell the TCCM when it is engaged, so it could be problem.

3) the encoder motor/module is bad. This is the module/motor that is mounted directly to the transfer case, who's job it is to physically move the gears of the transfer case to put the TC into the various modes (2Hi, 4Hi, 4Lo). You also want to check the wires at the encoder motor as they are exposed to the elements and *could* be damaged by something flying up under your vehicle (not likely, but possible).

4) the TCCM (which is what started this thread -- located under the passengers kick panel) has wires that are corroded / broken. Poor connections anywhere along the route will cause problems -- most times intermittently, which are a real PITA to find. (See my above posts for resolving this issue.) The TCCM could be bad as well.

If I had to guess -- either your encoder motor is shot, or bad wires on the TCCM. If you're really into it, I'll post the schematics for the wiring of the system -- this will allow you to trace and test points along the system to pinpoint the problem. (I have to scan them, so it may not be today!)

Well, I hope I have given you some direction to be able to start troubleshooting your 4WD system.

Regards;
Kyle

(UPDATED! 12/04/07 - Schematics have been added to the main post above.)

Thanks for the great pointers. I was able to figure out some of your more basic tips and verify that my front drive shaft is turning while in 4wd but not in 2wd. So far so good (it seems to me), so I'm investigating using my newfound knowledge re. vacuum lines etc. I was wondering if you could provide a bit more info with respect to the diaphragm that pulls the cable to the differential. I'm totally new to this and probably won't dive too far, but it's snowing here and the 4WD isn't working, so I'll hold the darn cable tight with vicegrips for a few months if I have to!!

Kyle's reply;

Hey Greg;

I'm not sure why you would want to pull the cable on the front diff -- I thought you said the front axle turns when in 4WD but not 2WD? If that is the case, the axle is engaged (meaning the cable is being pulled).

Now, there is a sensor on the front, right hub to detect when it is engaged -- I have not tried this, so I don't know 100% for sure, but if the front, right hub is not engaging, the system should detect this and NOT enter 4WD.

What you have to do is remove the battery and then the battery holder -- and you will then see the vacuum diaphram for the 4WD system. The battery cables are fairly short, so I removed the battery completely to work on the system, then put it back in on it's side to test it (but don't leave it like this for long -- it will leak!).

When you start the vehicle, and engage the 4WD system, vacuum will pull this diaphram closed and engage the front, right hub. So, start the vehicle and try to put it in 4WD -- watch the diaphram and see what happens. If it does not move, or only moves partially, you have either a leaking vacuum line, your vacuum switch is shot (see pic in a post above) or your diaphram is leaking.

Using a pair of ViseGrips will allow you to test the front, right hub, but I wouldn't recommend leaving it like that -- for one, the area under the battery is extremely small -- I couldn't get the ViseGrips on and put the battery back in place (which I wouldn't want to do anyway... just testing). Besides, the ViseGrips are going to tear up that cable and now you have a cable to replace as well.

Well, I hope some of this info helps you solve your problem -- good luck!

Regards;
Kyle

Kyle,
I have an '02 Chev 2500 with a manuel 4X4 shifter. My problem is that 4hi won't engage. 4lo seems to work just fine, axle engages, lights on the dash come on, I can hear front axle actuator engaging, but when I try 4hi nothing seems to happen. It feels like the gears are engaging in the transfer case but I don't hear the actuator engaging and the lights on the dash don't come on. Any suggestions?

Kyle's reply;

Hi J.P.,

Hmmm... my first thought is that it is a wiring problem. Why? Simply because you can prove that the system works by putting it into 4Lo. If you can get the system into 4Lo, that tells me the TCCM is working (or at least the 4Lo part is), the encoder motor is working, and the vacuum is working (the front hub is engaging -- the vacuum switch and diaphram are working). I'd check the wires are the TCCM first, then possibly the encoder motor next.

I've still got to get some schematics posted for another guest poster above -- hopefully I will remember to do so today. ;)

Regards;
Kyle

(UPDATED! 12/04/07 - Schematics have been added to the main post above.)

Hi I just bought a 2001 blazer with 34000 miles on it when I got it home I tried to get in 4-wheel drive but all I can get it to do is blink the lights on the dash, when I press the 4lo the trans goes in to 4lo but the front axle does not engage so whats do you think is going on. thanks Jon

Kyle's reply;

Hi Jon;

If the transmission engages, but the front hub does not, you have a vacuum problem. Now, this does not always mean there is a problem with the physical vacuum lines, or vacuum itself -- it *could* mean the vacuum switch is not getting power, which would not allow it to turn on, which would produce the effect of no vacuum at the diaphram and, well, if you have no vacuum at the diaphram, your front, right axle will no engage.

That, or you have major problems in the transfer case.

Regards;
Kyle

I have a 2000 Blazer also, and what a suprise have no 4 wheel drive haven't scinse last winter, anytime it was really slushy, or wet snow, you know when you need it, it would never work the next day it would, first it was the wires in the dash, they were cleaned put back together it worked..for a day or two, then the module, took it apart the whole thing...that worked for a while, now it's something else...not the module it's been checked, anywhere else on this thing that could cause problems with 4 wheel drive...used a test light there's power there, although the lights don't come on...please help the snow will be falling soon, and I hope this winter I might have the 4x4 I payed for...

Kyle's reply;

Hey E;

There's not much more that I can offer you, other that to say I will post the schematics later today. From there, at least you will know what wires go where and you can test them.

The first thing to check, though, are your fuses. If there are no lights on the dash, then you may not have "logic" power to the TCCM (logic power is +5VDC). The logic power is supplied through the courtesy lights (do your interior dome lights come on when you open the door?) -- check that fuse! (Fuse #8, I believe -- it's NOT listed as having anything to do with the 4WD system -- I found that through the schematics.) There are three fuses that I am aware of having to do with the 4WD system -- on under the hood (20A), one in the dash fuse paned (10A) and the other is the courtesy lights (15A, I believe).

I will get the schematics posted here as soon as I can.

Regards;
Kyle

(UPDATED! 12/04/07 - Schematics have been added to the main post above.)

I had someone help me and found out that the blazer had two problems. First, the hose from the vacuum actuator that goes to the firewall had a hole in it. Secondly, the switch on the encoder motor was bad.
Thanks for your help.
Although, I would like to get the wiring schematic from you, if your able to get one.

Thanks again

Kyle's reply;

Hey, that's good news -- glad I could help! :)

As for the schematics -- yes, but now it sounds like I am making excuses (which I am not!) -- I spent all day yesterday redoing my laptop and one (Windows) PC, and do not have everything back in yet (like my all-in-one center for my scanner). I actually sat down to do a little work on the site yesterday, along with updating my backup drive -- that's when the problems started. Anyway, before I turn this post into a rant... I have the schematics sitting right in front of me, ready to be scanned as soon as I am able to get this machine restored.

Thanks for your comments!

Regards;
Kyle

(UPDATED! 12/04/07 - Schematics have been added to the main post above.)

Hello again got my blazer out of the shop at one time the battery leaked out on that switch under the battery there for it wasnt telling the transfer case to engage got it repaired labor and parts 140.00 thanks Jon

Kyle's reply;

Hey $140 is pretty darn good compared to some of the quotes I have seen people get to fix their 4WD! :)

Regards;
Kyle

I just wanted to say that your site gave me the most insight to my problem and I also want to say thank you! My transfer case wasn't completing the shift into 4WD Hi/Lo and the buttons were blinking. Last summer I performed a tune up on the truck and noticed that a vacuum hose was worn. I didn't think anything of it except that my floor heat was probably going to blow in my face. The fix that I performed in the parking lot of the local auto parts store took 5 minutes and the vacuum coupler tube only cost about 75 cents. Thanks again for saving me a butt load of money!

Kyle's reply;

Hi Nick;

That's awesome!

Well, I think you'll take the cake -- I don't think we're going to see a repair for any less than 75 cents! Good work!

Regards;
Kyle

4wd will not engage? The lights on the dash dont blink, they are lit as if everything is normal, but no 4 wd. I checked all the fuses and they are fine. Could it be the vacume are something else?

Kyle's reply;

Hello Mike;

You aren't getting any flashing of the lights at all (when you try to engage 4WD)? There should only be one light on at a time (indicating which range you are in) -- multiple lights should flash when you try to engage 4WD (either Hi or Lo). If you try to engage 4WD and the lights do not change (ie. no flashing), I would suspect a problem with either the wiring to the TCCM or the TCCM itself is bad. I don't want to give you bad news, but I would suspect the latter as the lights will usually flash while the system is trying to engage 4WD, even if it doesn't engage, the lights flash while it's trying. If the lights don't flash, that tells me that the system isn't even trying to engage 4WD -- and that's controlled by the TCCM.

Regards;
Kyle

?? 1999 Blazer 4x4. When I try to engage 4x4, fuse under hood, "ATS" blows. Replace fuse and try to engage, blows again. Any suggestions??

Jim Frohner

Kyle's reply;

Hi Jim;

Well, that's one that I haven't heard yet. The "ATS" fuse (which is marked "ATC" on this schematic) supplies 12VDC to two large orange wires at the TCCM (marked as pins C18 and C19 on the schematic). As I said, I haven't seen this problem before, so I haven't traced that part of the system. I can only assume (yeah, I know!) that the because these wires supply 12VDC, they are used to run heavier things such as the encoder motor (5VDC, which is the light guage orange wire, is used for logic -- ie. to run the "chips" on the circuit board).

Hopefully, you can see where I'm going with this. I'm just trying to think about it logically -- if the fuse is blowing that supplies 12VDC, what in the 4WD system would use 12VDC? The encoder motor is the first thing that comes to mind.

Again, I have not tried this, but if it were me, I would try and disconnect the encoder motor and try again (this may not work as the system may detect the unplugged encoder and not try to engage 4WD -- the dash lights should flash if it's trying to engage 4WD). If you don't blow a fuse with the encoder motor replaced, you have found your problem -- well, sort of. From there it could either be the motor itself, a physical obstruction of the motor (the shaft could be frozen (corrosion) to the transfer case preventing the motor from moving) or wiring between the encoder motor and the TCCM (a short from supply to ground).

Good luck and let me know how it works out.

Regards;
Kyle

I have a 2001 Chevy S-10 unpredictable 4X4. The lights on the dash will blink when pushed, but nothing happens and it goes back into 2 wheel drive - my usual routine is to disconnect the negative battery cable wait for about 15 minutes reconnect the cable turn the truck on and push the 4HI button - this may work to put the truck in 4X4 mode 1 time or the fix may last for a month with no problems with switching from 2 to 4 wheel drive and back, but I never know when its not going to work. Any suggestions as to what may be going wrong? Your site is very informative. Thanks.

Kyle's reply;

Hi Sam;

Man, I hate "intermittent" problems -- they're, generally, a PITA to track down.

I really don't know what to tell you on this one -- but I'll give it some thought.

My first thought is TCCM problems. Disconnecting the battery is a standard procedure to reset any "OB (On-Board) computer" (although it's usually recommended to disconnect for 30 minutes -- simply so you don't rush it and it doesn't reset). So, what you're doing each time you do this is you are resetting the TCCM. From there, it works, but you never know for how long. Again, that makes me think TCCM. It sounds like there is something going wrong with the logic of the TCCM and it's "freezing" at a certain spot in the programming. This is, basically, like your computer at home (of course, we're only talking Windows machines here, not a real OS like Linux!) -- when it freezes, you turn it off and start again (reset). Everything works fine, but you know it will happen again, just not when.

The only thing I can suggest, which may be of no value to you, is to try and swap out the TCCM. You could try a used one from the scrap yard, but you never really know what you're getting there (you may be in worse shape). There are companies that rebuild them (the last one I heard my buddy at the garage buy was like $150, his cost, for a rebuilt unit), or, hopefully, your mechanic will have a good one around that you can use to see if that is the problem (of course, with the latter method, you will need to have a great relationship with your mechanic!).

Yes, all of the above "testing" of the TCCM may not be feasible for you. I know it's a problem that I would not want to tackle as I do not have access to another TCCM, so it makes like rough.

One of my hobbies is electronics design and programming -- so, if it were me, I would take the schematics (all schematics are in the first post of this thread) and start "probing" the TCCM to see what is doing what. I would record that info, and then do the exact same procedure the next time I had the problem to see what has changed. It may not help you actually fix the problem, but it will help you find it -- once it's found it can be fixed.

I know I've probably just rambled on and told you nothing -- well, that was simply my thought process when trying to find a problem. I can only hope it helped.

Let me know how you make out. If I think of anything else, I will update this post.

Regards;
Kyle

I don't know if you still have this site or not. The posts that I looked at
were from 2005 I think. I want to thank you for your time in keeping this
information on line. I had no 4wd in my 1998 s10. Your post said to check
several things and the 4wd actuator was my problem. Again, many thanks. Saved me $$$ for repairs. THANKS

Kyle's reply;

Hi Ron;

Yes, the site is still active -- actually, I can't believe how active (for my little blog site) it has been in the last few weeks -- and all about the Blazer! (I guess it's just that time of year when people are trying their 4WD! :) Hey, I'm glad I can help others fix these problems, instead of shelling out big bucks to the dealers.

If you don't mind, I would very much like to post your comments -- if you wish, I can leave your name out -- of course, the choice is yours and I will respect any decision you make, just let me know.

Regards;
Kyle

Kyle, you can post as you like.To add info, my dealer was talking about replacing the 2 computer modules associated with the 4wd, They said same as when they replaced them in '05 that both would have to be replaced at $1060 plus tax and that was a mininum. Again many thanks for your information. My 4wd is working now thanks to you.$60 for parts and one hour to reinstall. Ron bobbitt in West Virginia

Kyle's reply;

Great! Thanks again for the feedback, and allowing me to post your comments -- they are appreciated!

Best Regards;
Kyle

i have a 2000 chevy blazer sport model. my 4wd has worked fine up until we had a snow storm and i was trying to get back home on a hill. i attempted to engage 4wd hi by pressing the button, but nothing happened. i put it in neutral, pressed 4hi, and the lights blinked but switched back to 2hi. i pressed the button for 4low, and it switched and i was able to get up the hill. any ideas?

Kyle's reply;

Hmmm... could be a few things. First, if you can get into 4Lo, things probably aren't as bad as they seem -- this, basically, tells you that the components in the system are working. The TCCM is working, the encoder motor is working, the front, right axle is engaging, and your vacuum lines are working (there are more, but these are the important ones). The trick here will be to find out what is 4Hi dependent, and why it won't kick into 4Hi.

The next thing I noticed was that you said the lights on the dash will flash when you press 4Hi -- this tells you that the button for 4Hi is working, and the TCCM is accepting the signal from it. So, it boils down to a problem somewhere between the TCCM and the encoder motor -- I would suspect the TCCM -- possibly wiring, or possibly a bad TCCM. It's really hard to tell without being able to put my hands on it. However, you may also want to check the encoder motor signal lines (C26 through C28 on the pinout from the first post) -- they should be high (+5VDC) when the are not in use (resistors pull the lines high), and low when they are active (called "active low"). All schematics are posted in the first post of this thread.

Good luck and let me know how you make out (or if you have any further information / questions).

Regards;
Kyle

now that i have the blazer on flat land, i tried to engage the 4wd "on the fly" and nothing happened. i put it in park, and again nothing. the only way to engage it (no buttons flashing at all when in park or drive) is to put it in neutral, and again only will go into 4low.

i will check out the TCCM problems you mentioned. thanks!

Kyle's reply;

So, you're saying that the lights DO NOT flash when trying to engage 4Hi? That's a little different, with a couple more small things to check as the lights should flash if the TCCM is getting the signal.

The grey with black stripe wire (GRY/BLK) at pin 5 is the 4Hi signal wire -- when pressing the 4Hi button, this wire should go hot (I haven't test the wire, so I'm not sure if it's using logic levels (+5VDC) or battery power (+12VDC) -- either way, it should be hot when the button is pressed. You will want to check pin 5 of the TCCM connector, for sure -- as you can see from the original post in this thread, the wire harness at the TCCM is a problem -- specifically, pins 1 and 6 -- pin 5 is right next door to the small orange wire (pin 6).

Secondly, your dash buttons will pop out of the dash with little effort -- pop out the module and check the wiring harness on the back of that. I've heard of people experience problems with the actual buttons.

As I said, I have not tested any of the button wires, as I have not had that particular problem (yet) -- so, before you do this, you will want to verify what I am saying is true.

Put a test lead (volt meter) on the output of the 4Lo button... when you press 4 Lo, does the meter indicate that there is power leaving the button? (It should, if what I am reading here is correct... and I'm reading it correctly.) Now, do the same for 4Hi (do both tests in park) -- does it output the same as 4Lo? If not, you may wish to check the harness at the buttons a little more carefully first, and then try applying power to the output side of the 4Hi button (the same level as the output from 4Lo, whether it be +12VDC or +5VDC... I'm thinking it should be +12VDC though). Basically, this will emulate the button being pressed and should trigger the TCCM to engage 4Hi. If it does not, the problem is at the TCCM, most-likely. Again, check pin 5 at the TCCM. You may also wish to try applying power to pin 5 directly at the TCCM and see if it engages 4Hi.

If you are sure that the signal from the button is reaching the TCCM, then either the TCCM is bad, or the encoder signal lines have been damaged. Again, I'd have to test wires to be positive, but it appears (from the schematics) that the encoder signal lines are hot (pull-up resistors are being shown on each signal line) and are pulled low to activate a particular mode. Pins 26 through 28, on the TCCM pinout, are the encoder signal lines. Basically, test each of the lines -- if they are all hot while in 2Hi, then when you try to change to 2Lo, one of the lines should go low (0VDC) -- the same should happen with 4Hi.

So, if you try to engage 4Hi and you're sure there is power at pin 5 (4Hi button signal), and none of the lines change when trying to change to 4Hi, I would suspect the TCCM. If the encoder signal line DOES change, then the transfer case encoder motor module is bad.

Be logical, and methodical and eventually you will find your problem.

DISCLAIMER: Please note that I have stated numerous times that I have not tested any of what I have said here -- I am simply thinking about the problem logically while looking at the system schematics. TEST ALL WIRES before applying power to them.

Good luck and let me know how you make out.

Regards;
Kyle

Hi I have a 97 sonoma zr2 the 4hi works but going up hills it wants to slipp (loses power at hi rpms.) The 4lo light justs blinks all the time never goes in just goes back to 4hi. I here the clicking with the TCCM and I also hear the encoding motor working also.

Kyle's reply;

Sounds like your transfer case gears are worn -- I just had mine replaced with very few hours on them.

Regards;
Kyle

I wish I could find the schematic you are talking about. I found this link in your posts, but it doesn't work: http://www.kylestubbins.com/node/files/TCCM_power&ground.jpg

Thank you,
Sven

Kyle's reply;

Hi Sven;

Give them a try now (at the bottom of the first post). I have adjusted the settings of uploaded files, but I am not sure why you are seeing "node" in the link. The links should be http://kylestubbins.com/files/{whatever_the_file_name_is}.

Regards;
Kyle

Hey I have a 99 s-10 that is stuck in 4wd. It will shift from 4hi to 4low no problem. But will not shift to 2wd. The lights 2wd, 4hi, and 4low lights work properly. What should I look at? thanks, matt

Kyle's reply;

Hi Matt;

Hmmm... it's hard to say -- it could be as simple as the encoder motor signal lines being corroded/damaged (check the schematics in the first post), or it could be the transfer case itself.

If the lights work as they should, then this tells me the 4WD system is engaging, doing what it should. I suspect the transfer case is not shifting properly. As I said to a poster above, it may be time to have your transfer case checked by a tranny shop. The transfer case in this vehicle is weak -- it has a design flaw in it from the factory. There is a "fork" (for lack of a better term) with a plastic bushing in the TC that wears out and allows the gears to float -- mine were just replaced (the forks have been redesigned) with very few hours on them. In fact, mine were worn so bad that the gears had been rubbing the case and would have rubbed through the TC, had I left it as is, in the very near future.

Regards;
Kyle

UPDATED 12/12/07 - I just wanted to add to this post that the TCCM has two relays within that control the actual switching of the encoder motor -- you that is what you hear "clicking" when you try to engage the 4WD system. If you hear clicking going into 4Lo, but not coming out (to 2Hi or 4Hi), then you may also have a bad relay in the TCCM. Replacement of the TCCM will be required (unless you want to take it to an electronics guy who may be able to replace the relay for you).

Searched the Internet and found your site. My 4 Wheel Hi Light would flash for a few seconds and switch to 2 Wheel Hi, I followed you advice and found 2 corroded wires at the 4 wire connector on the T.C.C.M. which I cleaned. My lights would now flash and not switch back to 2 wheel hi.I went further and looked at the Vacuum Switch as suggested in your blog. I connected the vacuum lines together (while the 4 wheel light was flashing) and this engaged the 4 Wheel System. I reconnected the vacuum lines, lightly tapped the Vacuum Switch and it began to work like new. My guess is that the switch stuck due to lack of use. Without your blog the car dealer would be spending my money about now. Thanks!

Kyle's reply;

Hi Dan;

Thanks for the update -- that's what we like to hear!

I'm glad to have been able to help keep a few of those greenbacks in your wallet -- especially at Christmas!

Best Regards;
Kyle

i have a 1998 blazer and i have a similar problem to the rest of problems above. My 4 lo will work. and i hear the module click when it moves into 4lo. but when i try to move into 4 hi the lights flash and then goes directly to 2hi. i was wondering if you can plaese help?

Kyle's reply;

Hi Scott;

It's hard to diagnose problems like this without being able to test things -- but it sounds like either the TC encoder motor signal lines are bad (a bad ground can be a problem too) or the "forks" in the transfer case are worn, allowing the gears to float, in which case the gears for 4Hi may not be moving into place.

The first problem you can test yourself. Grab the schematics from the first post and test pins 26 through 29 for logic power (+5VDC), using pin 16 as your ground. You may also want to get under the vehicle and test the same wires at the encoder motor. Test the ground wire there as well.

The second, well, that's gonna take a trip to the tranny shop.

Regards;
Kyle

My service 4WD light came on, and the push buttons on the dash to activate the 4WD will not work. I checked all fuses in both panels, and the wires in the TCCM harness. Everything checked out. What next?

Kyle's reply;

Hi Jay;

When SERVICE 4WD appears on your Message Center it indicates that there is a problem with your Automatic Transfer Case. The system is designed to catch many problems before they become catastrophic. When SERVICE 4WD appears you should contact your local Chevrolet dealer immediately.

Now, I don't know if I rush right out to the dealer as there can be a few small problems that would cause this condition, depending on what that particular model/year has been programmed to detect.

Are there lights on the push buttons? Either way, the button module simply snaps into place in the dash and is easy to get out. Pull the button module and check for loose wires on the back of the switch.

I'd also check the vacuum actuator on the firewall.

After that, I'd pull the ground from the battery and let it sit for about a 1/2 an hour. Come back, attach the ground, cycle the key from on to off 3 times and try the 4WD system again.

Of course, your TCCM could be bad, as well as having actual problems within the ATC itself. That's the problem with systems like this -- it can be almost anything.

If you want to try out a few things and get back to me with some more info/questions, I'd be happy to try and help you through your problem.

Regards;
Kyle

I have a 98 Blazer, my 4 wheel drive a few months back would engage while I was driving in 2 wheel drive, causing a loud grinding or clicking noise, but when pushing the 4 wheel drive button the clicking would stop. I'm thinking that the 4 wheel was not fully engaged, caught between 2 and 4. Anyway I went to go use my 4 wheel drive the other day after snow and I hear the shafts engage but have no 4X4 at all. Could I have damaged the transfer case or wiped out the splines on the CV joints. How do I fix it and what much do you think it will cost. Any help would be greatly appreciated I should have took care of the problem when I heard the grinding noise

Kyle's reply;

Hey Tom;

I don't want to give you any bad news, but it sounds very similar to what I just went through... and it was the Transfer Case that needed service... badly. My Blazer probably only has 10-15 hours on the 4WD system, yet the "forks" inside the TC were badly worn and allowing my gears to float, which produced symptoms like you describe (among others). It seems this is a design flaw from GM and has been "updated" (my "forks", and their corresponding bushings, have been replaced with the updated parts... so we'll see).

The solution is to take it to a tranny shop and have the forks/bushings replaced.

Of course, I can't guarantee this is your problem, especially over the internet, and I hope it isn't -- but I would have it checked out professionally.

Regards;
Kyle

Hi,
I just wanted to say thank you for having this information posted on your blog. The info you have was a very big help is solving my problem. I have a 2001 Chevey Trailblazer 4x4. I was trying to use my 4 wheel drive this winter, and all I could get were blinking lights. My 2 wheel drive would engage but not my 4. I read about the tccm and the vaccum switch and to my certain amazement the vaccum line had broken off the switch. I fixed this issue and now my 4 wheel drive is working again. The info you posted saved me a trip to a dealer!!!
Thank You,
Greg

Kyle's reply;

That's what I like to hear! Extra $$$ for Christmas! ;)

Glad I could help, Greg.

Regards;
Kyle

I have and 2003 4wd blazer. When I engaged 4wd, the light will come on instantly but the 4wd will not engage. I hear the TCCM click when I engage and disengage. I also hear what sounds like air leaking when the drivers door is open and 4wd is engaged.

Kyle's reply;

Hi John;

That's odd that the light will come on instantly, without flashing and without engaging the 4WD. The solid light coming on at 4Hi is usually an indication that the system is functional.

Well, let's start with the most obvious problem -- the "leaking air" sound. Most likely this is a vacuum line that has either come off, or is broken. There are a couple of places this could happen -- however, hearing it with the drivers door open is probably an indicator that it's coming either from the mainfold, or the 4WD vacuum switch (pictured above, located on the firewall). The other spot for 4WD vacuum is under the battery -- but that is quite a distance from the drivers door, although anything is possible.

In short, start looking for a vacuum leak.

Regards;
Kyle

Hi it is scott again. You told me earlier that it was the ecoder motor. is there another name for that or what is it and where is it located because i have never heard of it?

And i cant use test pins 26 and 29 because mine only goes to 16. but there is a two side labeld c and d on the module connector. What am i suppose to do here.

Kyle's reply;

Hi Scott;

Hmmm, sounds like you have a different system there -- accordingly, I cannot help you any further as I can only help with what I am familiar with.

If there is no connector, like I describe, then you are going to need another set of schematics, and someone familiar with that system.

Good luck and best regards;
Kyle

PS - nope, no other name for the Encoder Motor, that I know of. It's located on the side of the transfer case and it what does the physical shifting between "modes" (2Hi, 4Hi/4Lo).

Hey Kyle,

I ment to mention, I had my transmission rebuilt 2 months ago and the 4wd worked then. I put my Blazer on jack stands and began tracing the hissing sound (air leaking?). I've discoverd the hissing noise is coming from the transfer case. I can here the encoder motor activating and deactivating. I wonder if the mechanics did something to the transfer case during rebuilding of the transmission. Anyway, what could be making this hissing sound in or near this transfer case.

Thanks for you help

Kyle's reply;

Hello again, John;

I, myself, don't know of any vacuum located at the transfer case, but I will try to find out for you (I have a transmission shop in the family -- I just called, but the knowledgable one is not yet in).

The TC is very close to the front of the vehicle -- are you sure the vacuum is not coming from the firewall area? The vacuum for the 4WD system starts on the drivers side, goes to the vacuum actuator in the middle of the firewall (but below the distributor and hard to see -- this is what I suspect you hear -- there is a picture up about 10 posts or so) and then goes to the diaphram under the battery.

If I find any further vacuum info, I'll post it here for your reference.

Regards;
Kyle

I have a 2000 Blazer 4wd. When I engage the 4 wd it goes into 4wd hi ok but after about 30 seconds the service 4wd light comes on. and it will not go back to 2w hi. thanks, great blog.

Kyle's reply;

Hi Dave;

Doesn't sound good. It sounds like what I just went through -- and it turned out to be the gears/forks in the transfer case. I first noticed that I had difficulty coming out of 4WD, then I started noticing 4Hi "slipping" in and out.

GM has a design flaw in this particular transfer case -- the "forks" had plastic bushing that will wear out and allow the gears of the TC float, and will not pull the gears into their proper positions.

I would recommend having it looked at by a tranny shop. The reason I suggest this is, if it is the problem I describe, the gears are actually rubbing the side of the transfer case -- and they will wear through, effectively causing a lot more damage than where you're at now (ie. complete replacement of the TC).

Thanks for your comments!

Kyle

Greetings. Here's what I got. If i press the 4hi button, the indicator lights up saying it is working. If I put the truck in neutral and press the 4lo it lights up as if it is working. Neither one seems to work as I got stuck in my driveway. Please help.

Kyle's reply;

You need to do some further investigation to provide more information -- there's all kinds of things to try posted above.

The first thing I would do is disconnect the battery and let it sit for a 1/2 hour or so -- then reconnect the battery and cycle the ignition from on to off three times -- this should reset the TCCM.

Regards;
Kyle

My sisters 2004 Blazer kicked out of 4-Hi one day while driving in the snow. She couldn't get it to work thereafter. I found that 4-Lo worked while in neutral, but if I selected 4-Hi I'd hear the relay click in the TCCM, the LED on the switch would flash on, but then it would go to 2WD.

So, I tried what Sam mentioned above, and also read in other message boards... to disconnect the battery for 1/2 hour to reset the computers. Low and behold, it works perfectly now. How long it will last I don't know... If anyone learns more about this problem, it would be great to learn what is going on.

Good Luck,
Sven

Kyle's reply;

Hi Sven -- thanks for the update -- glad you got it working again!

Regards;
Kyle

Hello, your postings seem very informative so i figured i would pick your brain for a sec. my 4wd would not come out of 4hi and i would get dim lights and hear the encoder motor wind up when i would try to engage it. several people told me that it was most deffinetely the encoder motor. so i tried to change it and when i did it put the transfer case into nuetral and the car goes nowhere and on top of that the 4wd error ligth on my dash will not go out.
should i be unplugging my tccm and resetting the system after i change to encoder motor. i thought it was a transfer case proplem because i thought it was binding up and not letting teh encoder motor start off in 2wd. so i just spent 7 hours on my back yesterday changing the transfer case just to find out that it is suppsed to be that way. i am out of my mind rigth now and that has to be one of the worst mechanically involved jobs i have ever been involved in.
so now i have a new transfer case and and a brand new encoder motor that i cant put on because it will not come out of nuetral on the trasfer case unless i shift it manually. and because i have to leave the encoder off the front axle wont engage because its not getting the rigth message.
please help!

Kyle's reply;

Hi George;

I do apologize, but I am not following you at all -- I'll try to answer some of your questions.

Yes, after replacing the TC or the encoder, I would reset the system by disconnecting the battery for 1/2 hour and then cycle the ignition from on to off three times.

If you can hear the encoder motor "wind up" -- the odds of it being shot are slim.

As for the rest of your problem with the TC being in neutral -- I don't know the answer to your question -- as far as I know, 2WD is neutral as far as the TC is concerned.

Regards;
Kyle

I have a 99' S10 Pickup and 4wd works fine but the front drive shaft will not disengage from the axles when switched to 2wd. Basically the transfer case is switching from 4wd to 2wd but the front axle is always engaged. I traced the cable cable back to the vacuum actuator under tha batery and found that the cable is not bound up but the actuator alway has vaccuum to it regardless if the vehicle is in 2wd or 4wd. It looks like the vaccuum is coming from a module on the transfer case but I was not sure how it all worked together. Anybody have any suggestions? I don't have a service manual for the truck, but am not opposed to buying one if it has a good section on trouble shooting the 4wd system.

Thanks
Dan

Kyle's reply;

Hey Dan;

Sorry for the delay in getting your post up.

It sounds like a problem another reader had, Amy, in this post.

Let me know if that helps.

Regards;
Kyle

First off let me start off by saying if it wasnt for this blog i probably wouldn't have any idea where to start in trying to fix my 4x4 issue. Like many other ppl on this blog i am having an issue trying to engage my 4x4. When i push the 4Hi button all the light does is blink. Following ur advise i checked the harness for any corrision and was amazed to find very little at all so i moved on the the vacuum switch. I found there that one of the hoses seemed to have ripped from the switch and it is no where to be found. Its the top hose and i was wondering if you could give me some insight as to where this one hose goes. Any help would be much apprecitated. It would make sense to me that if this hose was missing so would be my 4x4 lol. Thank you sir!

Kyle's reply;

Hi Mark;

First, I apologize for the delay in responding -- I had a crazy few weeks around the holidays and didn't do much blogging.

Unfortunately, I'm not really the guy to help you with the vacuum line as I've never had any problems with the vacuum and haven't had the need to trace hoses.

You might want to check this post to see if it might be of any assistance to you.

Regards;
Kyle

Hi Kyle. I can't thank you enough for this site! It saved me tons of time and money trying to figure out why my 4wd wasn't working. I checked the TCCM, repaired the wires...still nothing. Checked all the fuses and....problem solved. Thanks for helping me out! I'd like to return the favour. If you have a real estate question or one about renovations, just let me know.

Thanks again!
Blair

Kyle's reply;

Hi Blair -- great news -- thanks for the update!

As for real estate and renovations -- well, I'm also pretty well versed in both subjects! I like to buy old houses and rebuild them from the ground up. I just finished the house I am now living in -- a double brick home built in 1912 -- one of the first homes in my area. I've always meant to get some pictures up of the process -- I'll have to do that soon.

Thanks for the offer, and thanks for your comments, they are appreciated!

Regards;
Kyle

Thanks for the extra pointers. I ended up just taking it in to the shop because I was in over my head once I got beyond seeing the shaft turning and the need was urgent (truck doesn't drive worth a darn in ANY amount of snow w/o 4wd).

They ended up deciding my vacuum switch was shot and when I went back the new switch still didn't do the trick, so they figure it must be the actual pushbutton assembly on the dash. ugh. No idea what that's gonna cost, but I bet it's spendy. On the bright side they showed me where the switch was and how to manually enable/disable 4wd by splicing the vacuum lines together with a snippet of brake line :) Works like a charm in hi and lo now so that seemingly rules out the rest of the system. I was tempted to just manually join/unjoin the vacuum lines until Christmas debt is paid off, but I feel obligated to let them finish the repair now that the pushbutton is in.

Awesome blog thread!

Kyle's reply;

Hey Greg;

Man, if it's just a button assembly, don't worry -- there are no electronics in the button assembly -- they are just that -- buttons (switches). Meaning, it shouldn't cost all that much. The most expensive part will be the dealers labour rate.

Heck, if you want, run yourself a length of vacuum line into the passenger compartment and put a ball valve on it! :) (But, like you say, the assembly is in -- and it's much more professional!)

Thanks for the update!

Regards;
Kyle

HEY GUYS GREAT BLOG! i have a 2000 4x4 chvy s-10 blazer. (if its even worthy of being called a 4x4) same problems pretty much as everyone else...dash lites blink, i can hear the transfer case motor clicking and whining, but no 4 hi...4 lo works fine...sometimes both high and lo indicater lights will glow and the trans will seem like its slipping....then after i reverse and drive again it will finally slip into 4 low...already replaced the push button, and the differential motor...still same problem... my mechanics dang busted on what to do....i read something above about the mode forks being made out of plastic and wearing out allowing the gears to float...and something else about GMs design flaw... how do i go about seeing if there was a recall or something so i can get my pos fixed. us mountain boys up here in the do need all 4 weels turning at once. specially during this time of year.

Kyle's reply

Howdee!

You know, other than what I've posted above about the forks/gears, I don't really know much about them -- I had the problem explained to me while I was driving home on the highway in rush hour traffic. :) I never really asked any questions further than that -- 'cause my 4WD worked!

Mine would go into 4WD, both Lo and Hi, but would sometimes slip out of 4WD (mostly in Hi) causing a loud grinding/banging noise. When testing it in 4Lo, it would sometimes not go anywhere, then all of a sudden drop into gear like and snap your head back (with a hell of a bang as well). It stumped my mechanics for some time -- everything else was checked (they even ordered up parts for the front diff, and then sent them back) and it all looked good. The transfer case was the last thing they looked at (don't ask me why -- I guess the symptoms don't point to it).

First, I'd try resetting the system by disconnecting the battery for a 1/2 hour and then cycle the key from on to off 3 times. I know it sounds fruitless, but it has solved a few problems before now -- what's it take, a 1/2 hour of your time (and even then you can go watch TV!). Then, I'd maybe mention the forks/gears/plastic issue to your mechanic and he may be able to research it more. Don't hold your breath on a recall though -- if it's not a safety issue, and it lasts more than your warranty period, it'll never get recalled! ;)

Regards;
Kyle

Im posting this because recently i have worked on two s10 blazers with the same problem and everyone kept telling me to check vacuum and and the acuator. First off both of them the 4wd light would light like it was working but the front axle was not engaging i checked the acuator and it was working so i jacked the vehicle up and tried to manualy engage the axle with no luck. So i decided to pull the axle tube off the passenger side and check the locking hub. Pieces of metal had fallen out. Too my amzement both blazers had the same problem it was a thrust washer that that goes behind the axle courier connector works like a spacer. You can only buy these from a dealer the come in whats called a washer kit $10.40. Im posting this too help anyone out who has exhausted themselves looking at what everyone tells them too because the problem could be internal in the locking hub. I have a diagram if anyone has a similar problem. Ill send it to you if you email me at wildman510@yahoo.com

Kyle's reply

Hey Josh;

$10 to fix your 4WD -- awesome! Thanks for sharing that info with myself and my readers -- I'm sure it will help a few people save a ton of $$$!

I'm going to email you, as I would like to get a hold of your diagram -- hopefully you'll let me post it here to save people some time (and you from having to email it out to individual people all the time).

Thanks for your comments!

Regards;
Kyle

UPDATE -- Josh emailed me back with the following information -- thanks, Josh!

Click for a full size view

1. shaft 2.deflector 3.seal 4. bearing 5. tube 6.bolt 7. thrustwasher 8. retaining ring 9.carrier connector 10. shiftcable 11.shiftcable housing 12.gasket 13. indicator switch 14. Spring 15. seal 16. spring 17. shift shaft fork 18.bolt 19.tab washer 20. thrust washer 21. differential pilot bearing 22. sleeve 23. output shaft 24. washer 25. plug 26. washer 27. pin 28. bolt 29. carrier case 30. bearing 31. insert 32. sleeve 33. slide bearing 34. differential case 36.screw 37. pinion 38. shim 39. bearing 40. spacer 41. bearing 42. seal 43. deflector 44. flange 45. washer 46. nut 47. plug 48. bushing 49. vent hose 50. vent 51. fitting 52. shaft 53. thrust washer 54. side gear 55. thrust washer 56. differential pinion gear 57. cover 58. bolt 59. shaft

Number 7 has been the culpret in 2 of the blazers i have worked on its hardned steel so do not try and make one out of any washer it will fail. GM sells this washer in what they call a washer kit it includes 7, 20, and 24. If anyone has this problem its a simple fix and you dont even have to remove the diff, just the axle tube, but youll have to remove the halfshaft 1st this fix took me just over an hour to complete. I hope this info helps anyone with a similar problem. Also i have breakdowns of everything on these vehicles feel free to email me for something else i love your sight and believe info like this should be shared to anyone.

what is it with this number 1 and 6 pin lol awesome information kyle i read your stuff went out pulled it apart and sure enough that was it my 4wd is up and running now im getting a for sale sign because im tired of working on this thing lol thanks jay

Kyle's reply;

Awesome work, Jay! Glad I could help!

Kyle

I have a 1998 S10 Blazer with no 4wd.I checked The tccm,diaphram,and encoder motor which all seem to be working properly.The switch on the dash doesn't flash ,it lights up like it's supposed to do as if everything is working properly. The only thing i couldn't find was the vaccuum switch on the firewall. Any suggestions?P.S. great forum!

Kyle's reply;

Hey Raymond;

If I'm not mistaken 1999 and back, the vacuum switch is on top of the transfer case. 2000 and up it's on the firewall.

If it's on top of the TC, it looks like a nut with 3 hoses sprouting from it.

Regards;
Kyle

Hey all!! First off, I cannot lock into 4x4 while driving. My 2002 S-10 Blazer has the 3-button 2-hi, 4-hi, 2-lo. I, when playing around trying to get it to work, found that in order to engage the 4wheel drive I must first put it into Neutral (when completely stopped), then push the 4-lo, then go back to Neutral and push 4-hi. I cannot directly push 4-hi. It will only go into 4-hi after first being put into 4-lo. And sometimes, after getting it into 4-hi it takes a few tries before it wants to kick back into 2-hi. (very odd situation overall)

I checked the wiring harness behing the passenger kick plate and it is fine and in tact. The wires are all making contact.

If I push the 4-hi or 4-lo when in park or drive, I get nothing. No clicking, and the light will not light up. But If I do it from Neutral like I just explained, it works like a charm and the lights work as well.

Any Ideas? No one else seems to have had a problem like this from what I have read. I appreciate any feedback.. Does it sound like a vacuum problem somehweres?

Kyle's reply;

Hi Amy;

Actually, it sounds like the system is checking the neutral switch and will only actuate in neutral. 4Lo is supposed to operate this way, but 4Hi should switch on the fly.

Take a look at the schematic "front axel switch & pcm.jpg" -- and then have another look at the wires on the TCCM (Transfer Case Control Module), located under the passengers kick panel. Wire #1 (grey with a black stripe) is the PCM (Power Control Module) 4WD Lo signal line -- and is one that commonly corrodes.

The other wire I would check would be the A/T (Automatic Transmission) shift lock switch -- this is wire #31 and is light green with a black stripe (there are more pages of the schematics above... the first is a hand -written page of the TCCM connector pinout). This wire should have voltage applied to it at certain times -- unfortunately, I have never had to diagnose that part of the system, so I don't know if it should be +5VDC or +12VDC (but it will be one of them!) and I don't know if it should be hot when the transmission is in neutral or the other way around -- you'll have to figure that part out. What I would do is start the vehicle and test wire 31 for power -- then (obviously, with the assistance of a friend), put the vehicle in gear and test it again -- finally, put the vehicle in neutral and test it again. I would *think* neutral and park should be the same (I'd have to test mine to see) and the voltage would be the compliment when the vehicle is in any gear.

I could be wrong with this, but basic logics (and the schematics) tells me to start looking at the wire that prevents the TC from shifting if the A/T is in gear.

Good luck and let me know how you make out!

Regards;
Kyle

I have a 2001 S-10 with no 4wd. I can hear the transfer case engaging but nothing happens. checked the vacuum lines and there doesn't seem to be any leaks. No problems with the actuator either. The actuator seems like it is pulling the cable connected to the differential. The cable connects to a "pin" on the differential. With cable disconnected from the "pin" on the diff. I can manually move it in and out less than 1/4" in. This should pull out or push in closer to an inch or so right? Could this pin be flanged on the other end, not allowing it to pull out, or is there some other problem. Should I even open the diff. or just replace it.

Kyle's reply;

Hi Daniel;

Unfortunately, I have not encountered what you are describing and can only offer advise for things that I, personally, have done as I am not a mechanic. I do not know what this pin is, or how far it should move.

Regards;
Kyle