KyleStubbins.com

Hey Kyle (and readers)

I did recheck the TCCM and the wires were all fine and intact.

However, after playing around some more, I found that there was a bad vacuum switch on top of the transmission behind the transfer case. (I have been trying to post pictures.. but it isn't letting me.) -- see below!

What it is is a nut no larger than my thumb with 3 vacuum lines into one end and what seems to be a spring loaded ball on the opposing end. The one that I took off my blazer I can easily press this ball in and out of the casing. The new one I put in it next to impossible to press in. The end with the ball gets screwed into the transmission and it looks like the vacuum system controls the movement of that. (from my guess)

I paid $39.95 for the part and $45 labor.. total of $90.05!!

I probably saved hundreds if I would have gone to a dealer. I would have done the work myself, but I do not have a lift and that little part was a pain to access, or even get it out for that matter.

Thanks for your input, it was a great place to start. I hope this might be able to help any others with similar situations.

Kyle's reply;

Hmmm... thought I published this one -- sorry for the delay, and thanks for the update!

$90 -- what a nice feeling! ;)

Kyle

PS - I have changed the settings to allow registered members to upload images/files. If you wish to upload, you must register. Sorry, but the spam and other crap is just ridiculous anymore.

all indicator lites work and indicate 4wd is engaged or disengaged however no front axle engagement. i can hear the relay fire and hear what sounds like normal gear shifting in t-case. i removed battery and looked at actuator below appeared not to be corroded any help would be appreciated thanks josh

Kyle's reply;

Hi Josh;

Your problem sounds just like 10 others above you -- if you haven't found the answer in what I have posted thus far I, unfortunately, will not be able to help you and suggest taking your vehicle to a mechanic.

Regards;
Kyle

I am having some issues with my 4WD and came accross your site which helped me out so when I managed to get hold of these documents I though I would share them with you.
Thanks,
Ray.

Kyle's reply

Wow! What can I say -- I thank you, my readers thank you. :D

Regards;
Kyle

UPDATE 03/20/08

The links to the files have been removed as I did not realize they had been uploaded to a file server to post here. I should have backed them up to my server, but did not -- I apologize for that.

Kyle

The entire panel on driverside jsut stopped working. No power windows and no door locks. Also can not operate other windows. Where are the fuses for these? The box under hood does not say anything about door panel or windows.

Kyle's reply;

Apparently, under the rear seat!

Kyle

Hi Kyle,
I have a 2003 chevy blazer and have no drive to the front axle. When I push the buttons the tccm clicks, the buttons light and stay lit you can here the motor on transfer case run (for a brief time) and no power to front axle. I removed the battery tray found the diaphram and it is working. could my problem be vacuum? I guess I didn't look hard enough because I didn't see the vacuum switch by distributor and it's pretty tight in there . Any suggestions? Thanks,Tim

Kyle's reply;

Hi Tim;

It's hard to say what your problem is. I'd start with looking at the encoder motor -- if you can hear it run briefly, then what I would do is take it off the transfer case and try to engage 4WD then -- watch the motor and see what it does -- try it in all modes (2Hi, 4Hi, 4Lo) and watch the motor. If that seems to be OK, the next thing I would do is to try and manually shift the TC with the "tab" that should now be sticking out of the side of the TC (under the encoder motor that you removed) -- it is this tab that the encoder motor turns to engage the different modes. I can't tell you which way is which, but mark it where it is when you start and go from there (one way will be 4Hi, the other 4Lo).

Regards;
Kyle

I also have a 1999 blazer. The 4 wheel high button light is flashing all the time. The 2 high flashes if you push it and then goes off. the 4 wheel drive indicator on my instrument panel isn't lighting up and I don't think the 4 wheel drive is engaged.The TCCM clicks and we can hear a motor running if we push the 2 high button but the 2 high light flashes and then goes off. I can't get in to a mechanic for several days. My husband and I would like to know If we unplug the wire harnesses from the TCCM and leave them unplugged till I can get to the mechanic, will that harm anything? Thanks for the help

Kyle's reply;

Unplugging the TCCM isn't a great idea as it really doesn't achieve anything. If you are stuck in 4WD (which it sounds like you are), unplugging the TCCM will not get you back to 2WD.

However, I don't want to tell you to continue to drive the vehicle without knowing further information -- you may have a problem with the gears/forks in the TC which may not allow the encoder motor to physically switch modes -- of course, driving the vehicle in this condition would only cause greater damage.

The flashing light indicates the system is trying to enter that mode. If it stops flashing before it does, there was a problem getting to that mode.

Unfortunately, I'd say stop driving it and get it to a mechanic ASAP, if you cannot further diagnose the situation.

Regards;
Kyle

I have a 1999 Chevy blazer. a couple of days ago, my 4 wheel high indicator light came on and flashes constantly and the 2 hi light is off. The indicator light on the instrument panel doesn't come on and we don't think that the blazer is in 4 wheel drive. However, when I push the 2 high button it flashes and I hear a click click and a whir of a motor, then a click click and it goes back to the 4 high button flashing again. We have checked fuses,(all ok) the TCCM had a little corrosion but all indications are that it is working. One vacuum line was broken and we repaired it. We are not sure about the vacuum switch working correctly or not. I can't get into a mechanic for several days. What we would like to know is: Can we unplug the TCCM and drive the car safely until I can get it to a mechanic? Thanks for your help

Kyle's reply;

Hi Jenny;

First, please note that I am NOT a licensed mechanic! I like auto work and do most of my own work, and thus gain the experience that I share within my blog. OK, so enough of the disclaimers already! ;)

If by unplugging the TCCM you hope to that the vehicle will default to 2WD -- it won't. As long as it's actually working and driving your axle(s), leave it be and get it to a mechanic ASAP. I wouldn't recommend driving it for long periods, especially on dry pavement if it IS in 4WD though -- it is extremely hard on the drivetrain / 4WD system.

What it sounds like is you may have an encoder motor problem -- this is the motor on the side of the Transfer Case that controls the shifting of the various "modes" (2Hi, 4Hi & 4Lo). It could be leads to the motor, or the motor itself -- it's hard to say without being able to test things. At best, it's a corroded wire at the motor -- let's hope for that. :)

So, without physically removing the encoder motor module and manually shifting the Transfer Case into 2Hi, unfortunately, it's stuck in 4WD until you can get it to a mechanic. :(

Regards;
Kyle

Well after alot of time on my 2001 Jimmy 4wd system I am still stumped. Started with a clicking noise from front end so I checked vacuum actuator and it's doing it job now that I loosened up the cable. Truck will not go into 2hi or 4lo so I pulled the control module and checked wiring. Large orange wire on power connector was covered in corrosion and one wire on 32 pin connector was corroded. Fixed that and still no 2hi. When I attempt to change from 4hi to 2hi I can hear the encoder motor & vacuum solenoid on the firewall do their job and also the control module clicking so I presume it's doing it's job. I have 2 lights on dash causing worry, 'Service 4wd' & 'ABS'. Would the abs system fault prevent it from going into 2hi? I know your not a mechanic but have you any info for me?
Regards,
Ray.

Kyle's reply;

Hi Ray;

It does sound like things are doing their job -- I really don't like saying things like this as I am not a mechanic, so I could be wrong (hopefully), but it sounds like a transfer case problem to me. The service 4wd indicator light is "usually" caused by a problem with the TC, from what I have read on the subject (my manual states this as well).

As I said to a previous poster, if you want to get into it, remove the encoder motor from the TC and then try to engage the various drive modes -- and watch the motor to make sure it's moving in both directions (it should come to a stop in three different positions, for the three drive modes -- mark where it is when you start so you can put it back there if all else fails!). After that, you can try to shift the TC manually with the "tab" that will now be sticking out from the TC after removing the encoder motor.

Good luck!

Kyle

Kyle: Thanks so much for this web-site. It was key! I had a 1997 Chevy Blazer (4 wheel drive not working) only 2 wheel drive dash light on. I was looking at the actuator, and/or replacing the TCCM, but with the information I read on this web-site, I replaced 2 fuses , reset the TCCM, and bingo! It worked! Thanks for such an informative web-site.

Kyle's reply;

Thanks for the update!

It's nice when it turns out to be something easy! :)

Kyle

Hi Kyle , My pickup has three button set up[2hi 4hi 4lo] It won't shift into 4 hi on the fly or sitting in neutral.If press the 4hi button in neutral sitting still 4hi&4lo lights both blink then go back to 2hi moving nothing happens. It will go into 4lo stopped in neutral.Occasionally in neutral if I press 4hi and put it in gear, after I start to move it makes a bang and goes in but once I take it out it usually won't go back in.

Kyle's reply;

Hi Bradley;

You know, it sounds an awefull lot like what mine was doing -- which turned out to be the "plastic" bushings between the forks inside the transfer case. I really don't know a whole lot about the internal workings of the TC (I have the pros deal with that stuff), so other than that, I can't help you much -- sorry.

(Mine banged so loudly, I looked back to see if I left any parts on the road!)

Regards;
Kyle

I just replaced the Oxygen sensor on my 04 Blazer (which has been an electrical nightmare from the start). I got it swapped out fine but I was wondering if someone could tell me how to get the damn check engine light to go off now? Thanks

Kyle's reply;

Hi Michael;

If I am not mistaken, you cannot clear codes yourself -- you need to have someone do it with a scanner (ie. SnapOn). I could be wrong, but I don't think so -- I have a tranny shop within the family that has one, so I've never had the need to investigate it any further.

If I'm wrong, please let me know.

Regards;
Kyle

Thanks for this site. Hey kyle, I have a Chevy blazer LS and my 4WD does not work. when I press any 4WD button I can hear a click sound and the light associated with the button I pressed lights for a second or two and nothing happens. Per your aforementioned advice, I have checked the module to see if there is any visible corrosion but there isnt any. have any idea on how to fix this??

Kyle's reply;

Hey Moses;

Unfortunately, your questions are pretty vague and sound just like every other problem, as described above.

As I am not a mechanic, everything that I know about the Blazer 4WD system has, pretty much, been posted here -- you just have to read.

Regards;
Kyle

Hi Kyle
I am having a problem with the 4x4 on my 2001 Chev Blazer. I was checking out your blogs and I picked up a few tips on the problem, but I still can't seem to get it too work. At first it was making a clicking sound so I took it in to the shop and the mechanic managed to get it to go back into 2HI but right after that when I tried to switch from 2Hi to Auto trak it went right back into 4 Hi. So I parked it and pushed on the buttons and all of a sudden the service 4 wheel drive light came on, so I got frustrated and left it like that and today I was checking the net and I found your site and like I said t the begining I tried a few things and the servivce light came off but I still have no lights on the switches. So I am stumped if you have any suggestions I would greatly appreciate the feed back cause this is driving me NUTS

Thanks
Lenard Mercredi

Kyle's reply;

Hi Lenard;

You are going to have to give me some more information -- like what, specifically, were you doing when you got the service light to go out? What is the system doing now, if anything? Have you checked ALL your fuses (even the ones under the hood?). Did you check for corrosion on at the TCCM?

Keep in mind though, that the AutoTrack system varies from the standard 4WD setup. I don't know a lot about it, but from what I have read on the subject, the AutoTrack system is "set and forget" -- which may contain components not found on the standard 4WD system. Unfortunately, I cannot help you there.

Regards;
Kyle

Kyle: I have a clunking noise when in auto 4wd, 4hi and 4lo. The transfer is a np 246 is this case chain driven? Or could it be the bushing and fork that you described?

Kyle's reply;

Hey Tom;

Sorry, can't help you with that one -- the Silverado I don't know.

It sounds like you have AutoTrack though. As I said to a previous poster, I don't know much at all about AutoTrack, other than it's a "set and forget" type system. It may have other components, that are not on the standard 4WD system, that may be the cause of your problems.

As for the internal workings of the transfer case, I leave that to the pros so I can't answer that question either. :(

Regards;
Kyle

Im trying to track down my 4x4 problem. I have all lights on dash,TCCM connector is good and when I switch to 4 hi and lo I can hear the transfer case engaging and when I go to 4 lo and put in gear 4 lo works to the back wheels. Now Im trying to figure out my vacuum problem which I assume is the problem. I found the vacuum lines running to center firewall mounted switch. Now right near drivers hood hinge there is a couple of vacuum tee's and one has a short piece of hose running towards the fender with a screw in it. My question is should there be a resevoir on the drivers fender area where this line should have went to? There is no way that GM put a sheetmetal screw in it. My friend has a 95 blazer and there is a resevoir un the bottom of hood. What am I missing. I can send pictures if needed. Thanks in advance Shawn

Kyle's reply;

Hey Shawn,

If you sign up for an account here, you should be able to upload images here (I haven't had anyone try it yet, but I set it up after another guest said she could not upload images). If you want to email them to me -- click the contact link, shoot me an email and I will reply to it, which will give you my email address.

Regards;
Kyle

Sorry it took so long to get back. I repaced the encoder motor and all is well, working like a charm. You were right, if you disconnect the moter and try to engage, the dash lights up "Service 4X4."

Thanks again, Jim Frohner

Kyle's reply;

Hi Jim;

Excellent -- I'm glad that my blog was able to help you solve your problem, and hopefully save some money!

Regards;
Kyle

[Originally posted by "josh"]

great info on your site you saved me large amounts of cash$$$ turns out i had a bad actuator and was able to easily swap out the old part for new..never would have known where to start otherwise thank you josh

Kyle's reply;

Awesome! Glad to help, Josh!

Regards;
Kyle

PS - this was originally posted by a guest "Josh", but it was posted in the wrong thread -- and I couldn't move it -- so I reposted it.

First I have to say that this blog rocks!! I think you are doing an awesome service. I have read many of these problems but have not found one that matches mine exactly. A while back had the classic encoder motor problem where the truck would go into 4-lo or 2-hi, but would flash and default to 2-hi when 4-hi switch depressed. Well check vacuum actuator under battery, Tccm, encoder motor plug,etc and all was fine. Because my battery was disconnected the DTCs were reset and lo and behold my 4WD was working again. When 4wd was disengaged i would get a whirring noise out of the front end, like 4wd wasn't fully disengaging the front diff. I would stop the vehicle for a few minutes and it seemed to go away. The other day, on the way to work the noise wouldn't go away, so i tried putting it in and out of 4-hi a few times, until it blew the fuse. Replaced the fuse and immediately blew again, I was stuck in 4-hi. Came home that night, tapped on the transfer case and encoder motor with a rubber mallet, replaced the fuse and 4wd worked. Put truck in 2-hi and no noise. Started the truck yesterday and the fuse was blown again. Finally went and bought an encoder motor and replaced it this morning. Now nothing seems to work but TCCM(which seemed to work fine before). Press 4-hi button, and TCCM clicks about 5 times, then defaults back to 2-hi. Same thing in 4-lo. After trying this about 5 times, it won't even try to go in 4wd, just clicks and stays in 2-hi. Pull battery and it resets but goes back to the same problem. Remeoved the Encoder motor and reinstalled, no luck. Any ideas?? Do you think I got a bad encoder motor from parts store? I don'ty have enough hair as it is, I don't want to pull more out. Thanks.

Kyle's reply;

Hey Chris, and thanks for your questions!

What it sounds like, to me, is a wiring problem -- most likely between the encoder and the TCCM (under the kick panel). Have you pulled the kick panel and had a look at the TCCM wiring (as pictured int he first post of this blog entry)? How about the encoder motor connector? I would suspect the latter, a) because it is more susceptible to corrosion due to road salt, etc. and b) because you said the motor kicked in when rapping on the TC with a rubber mallet -- that probably caused shock in the connector/wiring, enough to engage the motor.

I'd check the wires that go to the various "channels" of the encoder motor. First, make sure you have "motor power" -- pins 6 (+) and 7 (-). According to the schematic (TC_encoder_motor), pin 3 should be signal ground, while pins 1, 2, 4 and 8 are the encoder signal lines. Now, I haven't done this, so I'm simply working from the schematic -- the lines are tied to +5VDC via a "pullup" resistor (as per the schematic, inside the TCCM) -- that's the squiggly looking thing where it says 5V. What I am assuming is happing is, the pullup resistor pulls the line high (give is power, so it should read +5VDC), the TCCM will pull one, or more (may be combinations for various modes, I don't really know) of the signal lines low to indicate the mode to the encoder motor which, in turn, moves the transfer case accordingly. Again, I'm working on some presumptions here.

What I would do is make sure you have +5VDC at pins 1, 2, 4 and 8 -- I would also use pin 3, the signal ground, as your ground reference when checking these pins -- make sure the signal ground is good. Make sure you have +12VDC at pin 6, using pin 7 as the reference ground. Remember, grounds are VERY important that they are GOOD. I might look a little harder at your motor power lines than anything -- it would be those lines that the fuse would be blowing (I would think -- but you haven't stated which fuse is blowing, and the 4WD system has a couple of them -- I believe I posted them in a reply here somewhere!).

The, you should try and put it in 4WD and see if any of the wires change (they should lose their power) -- you may have to do this multiple times to read the various wires -- and an assistant will be very handy!

If you're not getting the above results, check the same wires at the TCCM as see if the results change. If the do, the problem is in the wire somewhere between the TCCM and the encoder motor -- and I don't envy you having to find it, if that is the case. Using what I have said above, and some basic logic, you should be able to tell in the TCCM and encoder are communicating properly.

Other than that, it's possible that you got a bum encoder from the parts store, but how likely is it really? Try what I have said above and post back here if things still aren't working as they should and we'll see what else we can think of then. ;)

Regards;
Kyle

PS - I really hope I'm not way off base here and sending you on a wild Goose chase, but it's hard when you can't see the vehicle. It very well could be a mechanical problem in the transfer case causing the motor to draw excessive current and blow the fuse. Does the motor work well, when NOT attached to the transfer case?

Thanks for the reply Kyle. Due to the time and the temperature outside in sunny Buffalo NY, I won't be trying anything tonight. I am trying to do everything at work on lunch where its warm. To clear up a few things, I have checked the TCCM. I pulled the cover off and checked the insides and all looks good. Rusty on the out but no sign of corrosion inside the TCCM or the plug. I have visually inspected the EM connector multiple times. I have tugged on the wires, and it appears to be in great shape, no corrosion or apparant broken wires. Since the last post, I have exchanged the new EM with another new one and this one is exhibiting same problem so I am 99.99% sure it isn't the motor. The old EM worked when I tapped it with the mallet, but only for a short time, basically long enough to get me in 2-hi. Both new EMs have not worked. What is really bothering me is the fact that the new EM is installed and no blown fuse. Yesterday when I first put it in, the fuse blew within a minute of starting my truck. Today at work, (warm in our shop), checked the TCCM plug, pulled TCCM apart to check inside, cleaned anywhere the TCCM contacted the body to make sure it was grounded, replaced fuse and plugged it in. Once again it clicked multiple times and default to 2-hi. No blown fuse though. Cut tape and pulled wire loom off EM plug, and no apparant problem there. Had a helper watch 4wd switch as I #*@%ed with each individual wire and no fuse blew. I haven't tried the motor off the TC because the sheet with the EM said it would damage it. I know the EM moves freely and I checked to make sure the TC is free too. It moves with a crescent wrench with little effort. So I shy away from a mechanical problem. I am lost and aggravated!! I will try your suggestions ASAP, based on weather and time, and let you know. I want to fix it myself to say I did, but I am real close to giving it to my local 4wd pro and saying don't give it back til its ready for snow or mudding!! Thanks Kyle for your help, and hopefully I can get back to you with good news.

Kyle's reply;

Buffalo, eh? I hear you -- I'm just north of you in Ontario, Canada. You guys been getting pelted this week too? We got 8 inches yesterday, which started around 2:00pm -- just in time for the drive home. Thank God I had my 4WD yesterday (not trying to make you feel bad, honestly!) -- as I had 3,000 pounds worth of safes on the trailer and was in Toronto (about 50 miles from where I needed to take the safes). The drive took just over three hours -- fun wow!

Well, do what you can and let me know -- and I'll do my best to help you through it -- I'd like to see you fix it too!

Regards;
Kyle

PS - the flashing switch lights indicate the system is trying to communicate with the rest of the system. When it stops, it means it could not communicate with part of the system. Grab the schematics in the first post and check ALL sensors, etc. It really does sound like it's a wiring/sensor problem. You really need to make sure the encoder motor is getting the required power on all lines.

Hi. My problem is with my 04 Jimmy. I love the truck by the way. Here in Winnipeg it gets to -35 degrees C. overnight and in the morning my 4 wheel drive returns to 2 Hi. It seems that if I plug it in overnight that seems to help. Could a cold start and a sudden drain on the battery making the voltage drop to the TCCM make it return to 2 Hi? It is not that big of a problem because once I return it to 4 Auto or 4 Hi it seems to stay there for the day. Thanks for your help and love your website. John in frozen Winnipeg, Canada.

Kyle's reply;

Hi John;

Hmmm... that's a problem I haven't heard of before!

Reading your first thoughts on it, and I'd have to say I agree with you. Does the 4Hi light come on when you first turn the key to the ON position without attempting to start the vehicle? If so, and it returns to 2Hi after you start the vehicle, your assumptions are probably correct. Do you hear the TCCM click at all after starting the vehicle?

If you find that it IS your problem -- a diode and a capacitor should resolve the problem. What you do is get a diode (1N4148) and place it on the logic supply line of the TCCM (the polarity marker, a bad, towards the TCCM), and place a capacitor (100uF 36v should do it) between the diode and the TCCM. What this does is prevents the battery from pulling power FROM the TCCM (via the diode) and the capacitor makes sure you have enough power there to "temporarily" run the TCCM while the vehicle battery is being drawn from.

You may also wish to have your battery checked over. Winnipeg is hard on batteries, no doubt. My brother, who is a truck driver, had a battery freeze while in Alberta -- it was brand new and NOT covered under warranty. I'm in Ontario and I stood beside a guy in Canadian Tire the other night who brought a battery back and they told him the same thing -- no warranty, the battery is frozen. If you freeze a battery, you risk cracking the plates -- if you crack the plates, it won't hold a charge worth s**t.

Regards;
Kyle

Hi having a big problem with my four wheel drive it goes into 4 low and 4 high but it jumps out shanking the whole truck and then it will click until i put in back in 2 wheel. I had the front diff rplaced and the cv axles checked for damage but it still does it. Wondering if you could help me out? Thanks

Kyle's reply;

Sounds to me like the transfer case gears / forks -- if you dig back through some of the posts, I have described the problem you ask of.

Regards;
Kyle

Kyle:

I have Chevy 2001 Blazer. The problem I had is that I can't switch on the 4Hi. So I went to dealership. The repair costed me $900 to replace the TCCM. The dealer identified the problem as no power to turn on 4Hi. The TCCM model is $748 through dealer. I am kicking myself now. If I had seen your blog first, I could check the wire connection myself!

By the way, the dealer told me that 4Lo typically can not be turned on unless you put the vehicle in the neutral. If somehow vehicle goes into 4Lo by itself, just put it in the neutral position, and you can switch out 4Lo. I tested it and it works. I encountered the similar thing Spencer did and this is the solution dealership told me. A straight forward solution.

James

Kyle's reply;

OUCH! That hurts.

Yeah, this is really the reason that I put this information up in the first place. I had a ridiculous quote originally, and they (the dealership) hadn't even looked at it -- they were just going to start replacing parts.

As for shifting out of 4Lo -- there's just one more thing -- you MUST be going less than 2 MPH (3.2 KPH), with a "rolling engage" being preferred (ie. don't do this when stopped). This is a common mistake made when people have a "shift on-the-fly" type system.

Thanks for your comments, and hopefully next time you'll check the web first! ;)

Regards;
Kyle

Hey,
I hope this thread is still alive. Anyway, I have issue getting out of 4HI. I have read all of this discussion and Tried many things. I replaced the vacuum switch on the transfer case(mine was stuck). Then I checked all vacuum lines(some were cracked and I replaced). Pulled the encoder motor and cleaned it/took apart and re greased/sealed. Now, this is my current condition. If I unplug the TCCM, then plug it back in this is what happens. I start car, 2HI is lit and it is in fact in 2hi. When I press 4HI it goes in perfect. If I then press 2HI the 2HI light flashes (and you can hear the encoder motor moving and clicking below) But the 2HI light stops flashing after a few seconds and it stays in 4HI with that light illuminated.

I have found I can get it out of 4HI in one of two ways. If I park while stuck in 4HI and leave the car for a while, when started 4HI will flash and it reverts back to 2HI. OR If I put the truck in neutral, press 4LO (it goes into 4LO) then press 2HI, there is clunk and it goes back into 2HI. If it always worked like this I could deal with it, but after doing this a few times, the truck gets stuck in 2HI and doesn't respond to pushing any of the buttons unless the TCCM is unpluged and plugged back in. At that point the process repeats itself.Please help if you can!
Thanks,
Rick

Kyle's reply;

Hi Rick;

Unfortunately, I have not had experience with your particular problem -- but it does sound like it may either be a) the same problem as I was having (ie. internal gears / forks of the transfer case not allowing full shifting from one mode to the other), or b) a front axle switch problem (which is located within the Power Control Module (PCM) -- but that's about all I can help you with the PCM as I don't even know where it's located). The system is based on being able to communicate with all modules -- if it can't it will fail. If it doesn't know where the front axle is, it will do strange things.

There is a schematic (on page 1) of the front axle switch -- it appears to be tied to ground via a "pull-down" resistor. When engaged, it should be pulled high (+5VDC or +12VDC, I don't know what it's using for the switch).

I hope I've helped you, but I really am just guessing.

Regards;
Kyle

So, my four wheel drive use to work and recently stopped. Now all it does is the lights will blink when shifting into 4HI or 4Lo and blink for about 5 seconds then go back to 2HI. I hear a clicking that comes on. What are my possible problems?

Kyle's reply;

Are you serious? Did you read ANY of the last two pages?

Kyle

First, Kyle, great page! found it trying to find what is wrong with my Blazer. The 4 wheel drive will not engage...Was looking for the TCCM, you answered that question, Moving on to Amy, I noticed that my owners manual answered Amy's problem, it says that if you eventually end up having to use neutral to help engage... the transmission indicator switch may require adjustment.
Now where the heck that thing is...I have not got that far. Hope this helps all of us expand our knowledge on these great high maintance vehicles!

I may be back with some questions of my own...
got heat going in garage, will start ripping my vehicle apart! Ohh I forgot we are getting a storm of 12 inches, better start shovelin' best regards Doug

Kyle's reply;

Hey Doug -- thanks for the information! That makes a lot of sense -- now, if we can only find the switch! :)

If you think about it, the switch you talk about could just be the root of the problem for a few people who's 4WD won't engage.

I'll ask at the tranny shop on Monday to see if I can find out.

As for questions of your own -- fire away -- if I can answer them, I'd be more than happy to!

Regards;
Kyle

Lost 4 whl drive when switching from 4x4 auto to 4x4 hi..we heard a clunk sound ( i know not good) then only had 2 whl drive from that point on...
goes into shop this week..just wondering if it is a linkage of some sort? maybe u joint? The lights shows that the change into 4Hi is complete and 4 auto also..but just no traction from front wheels..maybe a transfer case issue?
thanks
joe t

Kyle's reply;

Hi Joe;

Well, seeing as you're taking it into the shop, and I am not a mechanic -- why guess? What's the point? Do I win a prize if I'm right?

You'll find out soon enough from your mechanic. In the meantime, there's two pages of Q&A above that you can read.

Regards;
Kyle

Perhaps you can help me. Today I left for work and my truck was in 2HI. About 5 minutes down the road no lights were on, in my 4x4 switch on the dash. I pushed the 2HI button and it lit right up. My truck does go into 4LO as I can hear and feel it engaging. My truck also appears to go in and out of 4HI and 2HI.I found a ice spot on the pavement and if its in 2HI it will spin , but when I hit 4HI I hear a slight clunk and it will take off like its in 4HI. My gas mileage on the other hand is way down. I am short 120 miles to a tank. I think my truck may be coming out of 2HI and engaging in 4Hi by itself.( when no lights are on the 4X4 switch on the dash I believe its either in 4HI or stuck in between. Is there a part that "holds" the transfer case in 2HI, 4HI, etc? Could a small vaccum leak cause this? Say I push the button, 2HI engages and then as I am driving down the road the vaccum losses its strength and disengages out of 2HI?

Sorry for the long post, I just don't know where to begin. Like I said I think my 4x4 works it just won't "hold" it in 2HI? Thanks for any help.

Kyle's reply;

Hi Jim;

The first thing I would check is the 4Hi light -- (keep it simple) -- does the 4Hi light ever come on?

It's possible that the system is engaging itself. However, 4WD engages WITH vacuum, not without -- accordingly, you may have a bad vacuum switch which is allowing vacuum through when it shouldn't.

Now, why the lights are going out, that is odd. I wouldn't think the system would "indicate" 4WD when it wasn't physically put there -- meaning, if the 4WD system DID happen to kick in due to vacuum, the TCCM would have never received a signal to PUT the system into 4WD and therefor would not move the encoder motor, or turn on the 4WD indicator lights. If the 4WD system is kicking in due to vacuum, the only real thing to be affected would be the front axle, which is what is controlled via vacuum. Hmmm, another thought just came to mind -- the actuator under your battery may be bad and the front passenger axle is stuck in the engaged position (the cable may be stuck) -- if that is the case, the front axle would be engaged but NOT being driven by the transfer case. That could, very well, be the cause of the excessive gas consumption.

Another option you may wish to explore is the TCCM -- have you looked for corrosion on the wires? Corroded signal lines could cause a condition where the TCCM "thinks" you're trying to switch to 4WD.

Well, that's a start anyway -- let me know what you find and we'll go from there.

Regards;
Kyle

PS - the "encoder motor" is the part that "holds" your TC in the various modes (well, that's not 100% accurate either -- the encoder motor shifts from one mode to the other -- parts inside the TC actually "hold" you in that mode -- in my case, it was a set of "forks" with plastic bushings that wore out -- which does not sound like your problem). For the motor to be bad is one thing, but for it to actually MOVE and shift your TC into another mode, that would be extremely odd if that was the case (if it WAS the case, I would still suspect TCCM signal lines to the encoder motor before I replaced the motor).

hi! to share my blazer story, trying to sell it, and low and behold the "service 4WD " light came on this weekend, and now unable to activate any 4WD and no lights on. Repair shop said it was the both the transfer case motor and the TCCM....adding up to almost $1000. I really do not want to spend this, and was wondering if you have any ideas. I already took a look at the wires and they seem o.k. the pins looked perfect, and maybe some corrosion noted on the wires, very small amount, and no broken wires...any input would be much appreciated. Also, the repair shop said that the TCCM got corroded and shorted out the transfer case motor....is this possible??
thanks!!

Kyle's reply;

Hi Tom;

I hear you on the cost -- it can be shocking.

As for your question of "is this possible?" -- of course, anything is possible. Is it likely? Or, would I trust what the dealer was telling me? Absolutely not. I have heard way too many horror stories with guys (and girls) taking their Blazers to the dealer. The TCCM is the fist thing they replace -- and hey, at $600-$700 (???), it's a two bolt and one harness connection money maker for the dealer. Hey, let's replace the 2 mosst expensive parts in the system and see if it works. Nevermind the fact that if that is NOT the problem, you're still paying for the new TCCM and encoder. $5 vacuum lines, and the like, are the LAST things to be replaced (how much money do you think they make off of replacing a vacuum line for you?).

As for the encoder motor being fried because the TCCM "got corroded and shorted it out" -- again, it doesn't seem likely to me. There are (off-the-top of my head) 7 wires between the TCCM and the encoder motor. 2 of them are power (+/-) and are FUSE protected. 4 of them are signal lines and the last one is signal ground. If the ground wire was corroded and shorted (to what?) it would not cause the encoder to fry. If any of the signal lines are shorted, again, it would not cause the encoder to fry as the signal lines are pulled high with a "pullup resistor" -- and are DESIGNED to short out to ground to pull the line low. At worst, if the signal lines were shorting out, you'd go into the wrong mode, or none at all -- but it would fry the encoder -- I'd be willing to be a weeks paycheck on that.

Regards;
Kyle

1994 chevy s-10 i have no 4 wheel drive response at all,what can i do ?Bill

Kyle's reply;

Drive it in 2Hi.

Regards;
Kyle

I have a similar, but not identical, situation. When I searched the net, I found another similar problem to yours and a reply. I'll summarize what I found then explain my problem, in the hope that someone might be able to help me. Many thanks to anyone who can.

I found a forum where a guy had a problem where his 99 Blazer would not shift to 4HI. When he pushed the 2HI button, the light flashed but nothing happened. Except that he heard a clicking noise coming from around the front wheels. The person responding said the problem is common, caused by a faulty actuator, and replacing it should resolve the issue. I hope this helps.

Like you, I also have a 98 Blazer but my problem is that it no longer switches from 4-wheel hi to 2-wheel drive smoothly. When I push the 2-wheel button, it continues in 4-wheel drive for about 1-2 minutes. Then, there is a jolt and a noise that feels and sounds just like I hit a pothole. In fact, that’s what I thought had happened the first few times. Instead, this jolt immediately precedes the 2-wheel drive being engaged.

I've tried stopping and putting it in park before switching and, although this did work some of the time, not every time. Also, during the time it takes to switch, the truck tugs slightly to the right. Just like it was slightly out of alignment. However, after it switches, the tugging stops.

There is no problem switching from 2WD to 4WD.

Mark Biggerman

Kyle's reply;

Hi Mark;

Have a look at this post --> More 4 wheel drive problems with my '03 Blazer (UPDATED).

It sounds like a similar problem I have already dealt with.

Regards;
Kyle

My service 4wd light is on my knob will not light up when turned I have nothing.. What do you think it may be? I really liked mt tb till right now.

Kyle's reply;

This is the last post like this you will see here -- I am getting so tired of the crap that is posted -- if you haven't read the last two pages of posts, or cannot articulate your question in am intelligent manner, your post will simply be deleted.

Please note that I get 5 times the crap in my inbox than I get posted here -- the same applies. If you don't get a response, you'll know why.

KyleStubbins.com is now a "moron free" website -- if you are one, don't bother posting.

Hi Kyle,

Thanks for getting my account working. I still can't figure out how to upload a picture. Anyway, great site, very informative. Like most here, I'm having a problem with my 4wd on my 2000 Blazer. I think it has something to do with the vaccum, but I'm not sure (been too cold out doors to really get into looking). Sure wish I could find a vacuum schematic. Anyway, on the drivers side, right at the firewall, I have a vacuum line loose. I took a picture, but like I said, I can't figure out how to upload it. I read in one of the previous comments, that there is a canister on the drivers side? This line is coming off of a tee just in front of the driver going toward the drivers side fender. If someone can trace, and perhaps let me know where it goes, this may solve my 4wd problem.

Best regards,

Jim

Kyle's reply;

Hi Jim;

In the right-menu, click the link "create content" -- from there you should have two choices; 1) create a forum topic, or 2) upload an image.

If you choose to start a new forum topic, you can attach files to your post. If you choose to upload an image, it will create a new topic within my blog (which I will then move to be included within your original post).

Or, as a last resort, please feel free to contact me via the contact form, leave your email address stating you'd like to send me some pics and I will respond with an address you can send them to.

Regards;
Kyle

UPDATE - 03/07/08

Hi Kyle,

Thanks for the instructions on uploading pics. Can you please add this to my original post. I'd really like some help on this. We are suppose to have about 6" of snow this weekend, and if this is my problem, I'll have 4wd for it. The hose I'm referring to is the one sticking out over the fender.

Best regards,

Jim

Click for a full size view

Kyle's reply;

Hello again, Jim;

I've got a 2003 Blazer, so I'll pop the hood this morning and see if I can find the info you're looking for.

And I think I'll go out now -- we're supposed to get 30 - 50 cm's between now and Sunday (that's 12 - 20 INCHES for you US guys!).

Regards;
Kyle

UPDATE - 03/07/08

I don't have all the terminology, or know what all the parts are -- but I can help you with the routing of the lines! The large black plastic thing you see IN the drivers side fender appears to be a vacuum canister -- whether lines come off it INSIDE the fender, I do not know. It appears to only have one line going to it, as can be seen in the picture. The bottom hose runs to the middle of the firewall, presumably to the vacuum switch, which is what engages your front axle.

Hopefully, this will help you figure it out!

Click for a full size view

Let me know how you make out.

Regards;
Kyle

Thanks for the pic. Kyle.

It's 2:30 Saturday, 3/8, and we have 12 inches on the ground, and it's suppose to snow for several more hours.

Best regards,

Jim

Kyle's reply;

I hear you Jim -- we got dumped on yesterday. We've had at least 12" fall in the last 24 hours. Towns East of me we supposed to be hit harder -- like up to 20".

Well, at least the sun is shinning this morning -- what a beautiful site with the fresh fallen snow!

Regards;
Kyle

UPDATE 03/16/08

Hi Kyle,

Thought I would give you an update on my 4wd situation. As I indicated in my original post, I had a vaccum line loose. I thought it went to a canister in the fender, what's more, I thought it had something to do with my 4wd not working. Well, that was the case. I found the attachment for that line on the canister. I acquired a new vaccum line (the one I had was weathered), installed it and hooked it up to the canister. Then I went to a muddy area in a sub-division next to mine, drove into the mud in 2wd. I just sat the spinning the rear wheels. Then I pushed the 4HI button, the light flashed for a second, then came on solid. I pushed on the gas and drove around in the mud like it wasn't muddy. MY 4WD WORKS! Thanks for your site, it's great. I wouldn't have ever thought that vaccum line would have kept me from having 4wd. By the way, my 4LO works as well. Of course it needs to be put into neutral before it will engage, per the owners manual. I've attached a diagram I received from the Chevrolet dealership parts department of some of the 4wd components on my 2000 Blazer. It did show me where the canister was and what to look for. Perhaps it will be helpful for someone else in the same situation.

Kyle's reply;

Awesome, Jim! I'm glad the posts here were able to help.

Thanks for the vacuum diagram! That will be very helpful for others trying to diagnose vacuum problems.

Regards;
Kyle

hi kyle, I own a 1995 chevy blazer. within the past week my four wheel drive would not engage, about two weeks ago I just replaced the distrubuitor rotor and cap, plugs and wires. at first I thought it would not engage because of the fuse but the fuse was good. I did a little research online and found out the most common problem - the vacume opperated acutator under the battery tray, so I replaced that and made sure the cable wasent binding or froze,everying worked ok but still no 4wd, so i did a vacume test of the system- 19 1/2 lbs per square inch which is perfect, then I did a vacume test on the hose that attaches to the accuator- 2wd = 0 lbs, 4 hi and lo = about 4 1/2 lbs of vacume. is that 4 1/2 lbs normal opperating range? i can hear the relay click when attemping to switch from 2 to 4 wheel, and i also hear the motor on the transfer case working, so my questin is, could it be the transfer case select switch be bad? or someting called the four wheel drive switch (HERE)? Please help me, i live in syracuse, where it snows ALOT!

Kyle's reply;

Hello Ryan;

Unfortunately, I don't know the answers to most of your questions -- I can guess, but that's what it's going to be, a guess.

As for the 4.5 pounds of vacuum -- it doesn't sound right, simply based on the 19.5 pounds you get from the base system. I'd check your hoses for a leak.

I am not familiar with the variances in model years -- I own a 2003 blazer, so what may be applicable to my vehicle may not be to your '95. Anyway, on the newer blazers, there is a vacuum switch, either located on the firewall (below the distributor), or on the top of the transfer case -- this switch controls the front, passenger axle (via the actuator/diaphram that you have already replaced).

As for the vacuum switch you linked to above -- could very well be the problem. For $18.95, it's cheap to find out! However, for pennies you can test it -- NAPA (and probably others, like PepBoys, etc.) will have vacuum hose connectors -- male to male connectors will allow you to stick 2 vacuum lines together. Remove the 2 lines from your switch and stick them together with a connector. This will allow vacuum to pass, regardless of the condition of the switch. Actually, seeing as you have a vacuum gauge -- test the lines as you remove them from the switch (keep in mind, 1 should have no vacuum, which would be normal).

Other than that, there are a couple of sensor switches -- one to detect if the front axle is engaged for sure -- which could also be a cause of failure (if the sensor says something is not right, it will kick it back out of 4WD and into 2Hi). Where they are located, I'm not 100% -- especially on a '95.

Well, that's about all I can think of right now -- if I think of anything else, I'll update this post.

Good luck, and let me know what you find -- in the hope that it will help someone else down the road.

Regards;
Kyle

hello, i came across your web stite and was impressed. i was hoping u might be able to help me out with my problem. as you can guess my 4x4 does not work. the service 4x4 light is on.i can here a clicking in the tccm. and when i turn my ignitionkey on. my push buttons light for a quick second but then go out. before the 4x4 went out i did have a problem with engaging the system and disengaging the system when i wanted to use the 4x4. any suggestions

Kyle's reply;

Hi Roy;

The service 4x4 light usually indicates a problem within the transfer case. Problems engaging a disengaging would seem to confirm this. Unfortunately, that is beyond the scope of this blog (and probably the average home mechanic) -- you need a professional -- take it to a transmission shop.

Regards;
Kyle

Your information has been very helpful, Thanks. My system is acting a little different than the postings I've read. My annunciator "Service Four Wheel Drive" comes on about two seconds after the ignition switch is turned on then goes out while starting the engine and comes back on as soon as the engine is running and the switch is released. All four lights on the 4wd selector come on when the ignition switch is turned on and then after a couple of seconds they dim. I have had problems with the four wheel drive in the past and discovered the corrosion at the connector on the tccm. Cleaning the terminals fixed it and another time I had flashing selector sightws and had to change the vacuum valve. The "Service" light Has come on befor but seemed to go out with the fixes. Any advice Kyle?

Kyle's reply;

Hi Daniel;

Unfortunately, I don't have any real experience with the service 4WD light. As I said to my guest below (just the order I answered the posts), it usually indicates a problem within the transfer case -- trouble codes should be set, so you may need to have it scanned by your mechanic. Other than that, I cannot really offer any further advise -- all of my experiences with my Blazers 4WD system have been posted here.

Regards;
Kyle

light comes on when it is put in 4x4 and comes off once you shut vehicle off for 5-10 seconds and you push 2 wheel drive button, any help would be appreciated

Kyle's reply;

Generally, that is telling you that there is a problem in the transfer case -- trouble codes should be set, so have your vehicle scanned by your mechanic. I have no experience with the 4WD service light, so other than that, I have no further information.

Regards;
Kyle

Hi Kyle
I cannot download any of the files/documents which you posted from Raymond Dunne (2008-01-03 19:30).
Indication I get is that the files are no longer available.They may have been deleted by the uploader, or expired.
Is it possible for you to relist them? From the titles these documents would appear to be very useful in diagnosing Blazer/Jimmy 4x4 problems.
I thank you in advance.
Les

Kyle's reply;

Hi Les -- I didn't realize that Raymond had uploaded them to a file server -- I thought they were part of a site that stored that information (ie. an auto info site), or I would have saved them on my server. My bad.

However, I looked and do have an email for Raymond... I'll send him a message and see if it's possible for him to email the files to me.

Regards;
Kyle

UPDATE -- 03/20/08

Hi Les -- I'm going to have to say no as Raymond no longer has them -- again, I apologize for not backing them up.

Regards;
Kyle

UPDATE -- 03/20/08

Hold onto that thought for a few days -- some software is on the way that will allow me to retrieve the files.

Regards;
Kyle

I am having a problem with my 4WD not going into 4HI, I press the button and nothing happens. I put the truck in neutral and hit 4LO it goes in, then I press 2HI and it goes back. When I have it in neutral and press 4HI both 4HI and 4LO lights flash and then goes back to 2HI. I read that if you jumper pin 13 on the data link cable to ground, then turn key to the ON position the lights on the 4WD buttons flash a code, so I tried it and sure enough a code of 2 flashed meaning motor/encoder failure. I haven't changed it yet so I don't know if that is the problem. I am going to check the TCCM connections. Just to let you know there are only 4 codes. The first is 1 flash meaning RAM stand by power to the TCCM was lost. 2 flashes means motor/encoder failure. 3 flashes means motor circuit failure. 4 flashes means TCCM needs to be replaced. I hope this helps you in some way and if I am incorrect please let me know. Thanks Rudy

Kyle's reply;

Hi Rudy;

That's some pretty good information to have.

Please do let me know how you make out with the encoder motor replacement.

Regards;
Kyle

Thanks for the response to my post earlier, and i had pep boys do a vacuum test on the system and they said every thing was seemed to be ok, so i bought that four wheel drive swith from napa and installed it,(it went into the front axle right where the cable from the actuator attaches), still no luck. so i could see some kind of sensor on top of the transfer case with 3 vacuum lines attached to it, so i replaced i, and once again still nothing, so i have a couple more questions...their is another sensor on the tail pice of the transfer case, i was told it is the speed control sensor, could that be the problem? and do you know if the transfer case would not engage due to low fluid level? i dont want to replace the fluid unless i have to. and would you know how to determine if the switch itself is bad? And do you know how would i tell if the control module under the dash is bad.

Thanks for your time,
Ryan

Kyle's reply;

Hello, Ryan. Again, I am not a mechanic, so I really don't know the answers to most of your questions. I can only offer what I, personally, have had experience with. I will try to address what I can.

Your question regarding the speed control sensor -- this could cause a problem, but I guess it depends on if it's a transmission speed control sensor, or a vehicle speed control sensor. 4Lo will only engage under 8KM (from memory, I believe it to be correct), but 4Hi is shift-on-the-fly and should engage at, pretty much, any speed (from memory, I think it may not shift above 100KM, but I'm not sure on that).

Could low fluid cause a problem? Yes. You don't have to replace your fluid if it's low -- just top it up to the proper amount. However, I'd be asking myself WHY it's low.

How to test if the switch is bad? I'm not sure which switch you're talking about, but no, I do not. I'd simply Google it most of the time to find what I'm looking for. Everything that I ever wanted to test was found through Google.

How to tell if the TCCM is bad? Well, that's a little too involved for me to detail here (basically, it involves systematic testing of the various wires). If you can read a schematic, then you'll know what to do with it -- all schematics that you'll need are in post 1 of this thread. If you look at the schematics and still don't know what to do (and I'm not being smart), the job is over your head and you should take it to a professional.

Unfortunately, I don't really have any advise that is going to help you any further.

Regards;
Kyle

Hope you still look at this every now and then. My blazer dropped into 4 low after backing out of a parking place at work!! Now I can't get it to go back into 2WD or 4 HI. It's stuck in Low range. The electrical box in your thread gives me the all good "click click" when the key is turned. Any suggestions?

Kyle's reply;

Sorry, but no -- what I know about the Blazer 4WD system has been posted within this thread.

Regards;
Kyle

i have a 2001 blazer no 4wheel drive lights flash when you push button i changed tccm,motor on tranfer case,acturator under battery need to no what else to look for thank you craig

Kyle's reply;

Fuses?

Kyle

I was driving in 2 hi going down the highway and looked down and saw my 4wd-lo flashing it stopped flashing on it's own and stayed in 2 hi. Yesterday my wife went to wash the car and it did shift into 4wd lo on it's own. I had to manually change it back to 2hi worked fine then like i said i saw it flashing today. What does my problem sound like and how can i fix it and the cost involved and is there a chance when going down the highway at 60 mph plus all the sudden it will shift into 4 wd low and my tranny could get ruined. This is a used tranny I got put in last November.Thanks

Kyle's reply;

Hello Mike;

First, your tranny will not shift into 4Lo at 60 MPH -- it is designed to shift ONLY when the transmission reaches speeds of 3MPH (5KM/H) or LESS. The flashing indicates that the TCCM is trying to shift from 2/4Hi to 4Lo, but it cannot due to the speed currently being traveled (hence why it went into 4Lo for your wife at the car wash) -- it will flash for 30 seconds (I believe it's 30 seconds) and then revert back to the mode it was last in (ie. 2/4Hi).

I always start with the simple stuff and work back from there -- what it sounds like to me is the button assembly on your dash, a wire between the button assembly and the TCCM, or the TCCM itself is bad. I'd start with the easiest, and cheapest part -- either go to the dealer and order a button assembly, or go to your local scrap yard and yank one out yourself. If that doesn't work, you have two options left with the wires and TCCM.

Some how the system thinks the 4Lo button is being pressed, and that's what you need to find. Unfortunately, intermittent problems are the toughest to find. That being said, I wish you the best of luck. Please let me know when you find the problem as I would like to have the info here to help others with the same problem.

Regards;
Kyle

i just bought a used 97 blazer 4x4... in Fed. we had an ice storm and i put in it 4x4 hi and the 4lo the lights came on stating it was in 4x4 but i could not tell a diff between it and 2 wheel drive.. this is my 1st 4x4 truck.. how can you tell if 4x4 works or not.... also we got about 5 inches of rain over a night i was already parked in the mud and the next morning i tired 4hi and low again and nothing but spinning my front 2 tires it looked to me as the back 2 were not pulling at all... thats why i am asking this question... i was told that if a truck is already stuck in the mud then 4x4 will not make a diff is this true?

Kyle's reply;

Hello Guest;

If you say your front wheels were spinning and your back 2 were not, your 4 wheel drive is working (although I'd be concerned as to why the back to wheels were not working -- they are the two the drive the vehicle in both 2 and 4 wheel drive. If the front 2 wheels are driving, you are in 4WD.

Besides that, you'd know if you were in 4WD or not. Like you said, park in the mud -- put it in 2Hi and try to get out. Then put it in 4Hi and do the same. There should be quite the differenc in feeling between the two modes in mud. If there is not, a visit to your local mechanic is in order.

Regards;
Kyle

Hi Kyle........you have a great site and have read just about every item you and your readers have issues with but my wifes truck has the Grand Daddy of problems and if you tell her to sell it she will understand. Here goes....I was allowed to drive her around the other day when I heard what I thought was the blinker going and tried repeatedly to cancel the non blinking lites with no success. After a few minutes the service 4 whl drive lite came on, when we parked I asked if this had happened before and she said yes all the time but it goes away when I park. OK I said. we shopped and came back. I started up the truck and when I put it in drive it gave a strange lurch forward. It had shifted into 4 whl low. There are no lites on the push buttons and it will not shift out using any of the methods in other strings above. The kick space module is impeccable, I even took it apart looking for a cold solder joint, no such luck. The vacuum module under the battery works great as does the vacuum switch above the distributer. I suppose at this stage I will have to crawl under the truck. Or do you think I will be wasting my time? Any suggestions will really help. thanks Bob

Kyle's reply;

Hello Bob;

First, I apologize for the delay in responding to your question. I have no excuse -- I've been neglecting my site recently.

As I said to a poster above (two up from this one), it sounds to me like it may be a button assembly, wire between the button assembly and TCCM or a TCCM problem. The system "thinks" a button is being pressed and trying to shift to 4Lo. Now, I'm making suggestions here, but I have not tried this -- there may be a little figuring out to do, but the schematics in the first post should help you out.

What I would do is test the button assembly wires at the TCCM. If I'm not mistaken, I believe that the buttons are pulled high (+5VDC) and ground out on pressing them (I could be wrong, so please double check!). So, I'd test each one of the button assembly wires at the TCCM. The should all be the same with no buttons pressed. I'm thinking it sounds like your 4Lo button is stuck (or a wire shorted). If it's stuck, pressing other buttons won't do anything. However, what does have me stumped is the fact that the service light comes on... but that could be caused if the system detects a stuck button (I don't know how much diagnostics the system does on itself).

Oh, the clicking you hear is, most-likely, the relays in the TCCM trying to shift into 4Lo. If you come to a stop while you hear that, you'll probably shift into 4Lo (your speed must be less than 3MPH or 5KM/H to shift into 4Lo and is why it keeps clicking as you drive -- it tries to shift for 30 seconds, then gives up).

Hopefully, this will set you off in the right direction. Please let me know what you find as it may be of use to someone else here in the future.

Regards;
Kyle

Thank you all for this excellent forum. After reading it, I checked ALL the fuses and found #3 for "PK LPS" blown. Changing that fuse got the the 4WD working again.

Kyle's reply;

Hey Adam;

Awesome news! I'm glad we were able to help you solve your problem.

Regards;
Kyle

I have a 2000 s10 blazer and am having issues as well, when I push the 4hi button it will light into 4hi, but pulls severely to the right. So I have not been using ny 4 wheel drive. But when I get into slippery conditions the 2hi light will turn off, it eventually, maybe the next day will come back on, but just an odd thing. Any ideas appreciated. I am pretty mechanical so I understand some of this.

Kyle's reply;

Hi Beth;

Normally, the front drivers axle is the axle that is permanently engaged within the front differential (that doesn't mean it's always driving... only when the front diff is engaged will it actually drive). The front passenger side axle engages when put in 4WD, via an actuator under the battery. So, if it's pulling to the right, it leads me to believe the front left axle is not driving (which would be odd). There's not much I can suggest to you for this situation. The only thing I can think of requires a hoist -- put the vehicle up on a hoist and engage 4WD, then check the front drive wheels/axles.

Your comment about getting into slippery conditions and the 2Hi light goes out... the only thing I can think of is the TCCM (Transfer Case Control Module) may have corroded wires, which was the original topic of this thread. Does this happen automatically when you get into slippery conditions? I mean, do your wheels spin in slippery conditions and THEN the 2Hi light goes out? Or do you have it in 4WD and under slippery conditions (again, I'll assume your wheels are spinning) it reverts to 2Hi but does not indicate so via the dash lights until some time later?

It almost sounds as if you have two, independent problems with your 4WD system.

Regards;
Kyle

I am so tired of telling people I AM NOT A MECHANIC, that I am closing the comments section of this post.

I post what I have encountered during MY OWN REPAIRS -- I post this information and state that, but somehow people never read the posts, yet they leave feedback or comments asking me how to fix something that I know nothing about.

Again, I AM NOT A MECHANIC!!!!!! Got it?

Do NOT use my contact form to ask questions about your Blazer as they will be ignored.

If it is not posted above, I CANNOT HELP YOU -- GO TO A PROFESSIONAL MECHANIC!!!!!

Today I am reopening the comments section of this post. As you can read from my comments above, it had become really frustrating that people wouldn't read what I had posted and would ask the exact same question to me in the comments.

Well, it's becoming more frustrating getting those same questions over and over and over... but now in random threads! Anyway, the comments for this thread have been reopened so I can, again, reorganize the comments from other threads and place them back here.

Please, read what has been posted before asking your question. Again, I am not a mechanic. What I have posted here are simply my personal experiences. It's like fixing your plugged toilet, posting about it and now everyone thinks you're a plumber.

We'll see how it goes.

my 4 wheel low will work in neutral when you select 4 high or 2 hi you could hear the relay come in. when you hit 4 high the 4 wheel low and 4 wheel high comes on at the same time if you hit 2 high the relay comes on put no light I put the tccm module in to another truck and it works fine.the vacumm actuator only come in 4 wheel low i replaced the vacumm module.I check all the voltages at the module the 4 pins with encodor has the 5 volts on it one of the 4 pin the voltage drop to 4 volts then to 3 volts the other 3 pin drop to 0 volts is ok?when you put it in gear the relay wont come in 4 wheel high or 2 high so i cannot find any thing that control this

Kyle's reply;

Did you even read the comment directly above this?

Take it to a mechanic.

Kyle