KyleStubbins.com

I have checked and fixed everything like above. How do I know if my 4WD is working on dry ground with any snow yet?

Kyle's reply;

On dry ground... you don't. Take it to a mud hole, or wait for it to snow.

Regards;
Kyle

Thats right...

2 Quick visual inspections could fix your problems with the 4 wheel drive not working, flashing lights, wont go into 4whl low. I learned alot reading this blog and wanted to ad the onfo I gained and the results I got in about 30min. from 2 visual inspections.

This first Inspection: Start with the pass side kick panel, remove the panel and inspect for corrosion, loose or broken wires, Clean and repair as needed.

The Second Inspection is in the engine bay high up on the center of the firewall. Inspect for vacuum at the switch and then make sure the hose is'nt damaged causing leaking (Mine was broken off) Excess heat from the engine compartment will damage vacuum hoses and excessive curves or bending will lead to problems with hose decay and failure. I cut off 2 inches and replaced the hose.

That took me about 30 minutes and corrected my inop 4 whl Drive on a 2001 Blazer.

Thanks a lot for the advise!!!

TK

Kyle's reply;

Hey TK!

Just one note... not all vacuum switches are located on the firewall. If it's not there, check the top of your transfer case!

Thanks for your comments, and the info!

Regards;
Kyle

You are a hero to many people! Looking at your blog it appears you have saved people hundreds if not thousands of dollars by helping people fix their 4WD problems themselves. I solved my problem after reading about vacuum leaks. Sure enough the vacuum hose had broken off the switch on firewall. It appears the hose was too short to begin with and was kinked causing it to fail prematurely. Armed with 3 inches of hose and a connector it now works like a charm. Since the system has never worked while I've owned it, I have one question. When I push the '4WD Auto' button it takes approximately 10 seconds for it to engage. Is this normal or is something else wrong. It seems to work fine. My only concern is it takes a long time for the light to stop flashing and stay lit.

Regards,
John Boy

Kyle's reply;

Hi John Boy;

A hero? Hardly! :) But hey, if I can help out a few people with my ramblings, awesome! Glad to have helped.

As for the answer to your question -- sorry, I don't have the foggiest as my Blazer doesn't have the "Auto" feature. Ya gotta own one of them fancy trucks! :) You know what I'd say though? If it ain't broke, don't touch it!

Thanks for your comments!

Regards;
Kyle

I have a 2002 trailblazer lt and no 4wd. Last winter my service 4wd kept coming on and i had to have the tccm replaced. Well now this winter i was driving through a field of course in a4wd and as soon as my front tires grabbed it shut off, service 4wd light came on and dash light stayed in A4wd for about 15 seconds and then lights turned off all together. I brought it in and they told me the encoder motor was bad, ok well easy enough ill just have them fix it. Then i was told that when the encoder motor goes out, the tccm also goes out, is that true? I can deal with fixing the encoder motor, but if i have to replace the tccm again ill be very angry!

Kyle's reply:

It sounds more like "mechanic talk" to me -- but who am I? :) What exactly do they claim to be the problem with the TCCM? What part of it is bad? Ask them what would cause that. There are schematics at the beginning of this post... print them out and show them to them and ask what is bad and why. That's really all I can offer other than my opinion.

If you look at the schematics, you can see the motor is simply "controlled" by the TCCM via signal wires. I guess it's possible that if one of the motor wires were to be shorted it may cause damage to the TCCM -- do I think this is the case? No. If I recall, the schematics show a pull up/down resistor on the DC lines... this should prevent damage at the TCCM due to shorting.

Again, if I recall, the 12VDC source for the encoder motor is also supplied through the TCCM... that could produce quite a bit of current, if the motor was damaged.

What I'd do is go out and start testing the TCCM and connections (if you have that capability). I go through quite a bit of it in this post. Check to see if you're getting a 12VDC source at the TCCM to start with. I believe it's the big orange wire (from memory...check it out in the schematics!). Look at it logically, and start testing.

I really don't have the experience to say definitively yes, or no -- but I wish you the best of luck. Please, let us know how you make out.

Regards;
Kyle

Hello,
I have 2001 S-10 Crew Cab. When I push my 4hi or 4lo
switch nothing happins. Now when I put the truck in neutral nothing in 4hi but it will go to 4lo. Then I can push 4hi and it will go in. Then I can go back to 2 wheel. But the only time I can do any of this is when It is in neutral and at a complete stop. Any Ideas. Thanks

Kyle's reply;

Hi Steve;

Although I don't really have any experience with the problem you describe, it sounds like a switch / sensor to me. I do know there is a speed sensor that stops you from putting the system into 4Lo while you are traveling at a speed of greater than 5MPH (8KMH) -- if that is the case, the 4Lo light should flash until you slow down to under 5MPH, then it should drop into 4Lo.

The system *should* drop into 4Hi at any time (OTF - On The Fly), up to speeds of 80KMH (I believe that is the figure... that's from memory).

It sounds "electrical" to me... accordingly, the first place I'd start looking is at the TCCM for corrosion. Then, I'd take a look at the schematics posted within this thread and start looking for sensors.

Good luck and let me know how you make out, or if you have any further questions.

Regards;
Kyle

Hi, I don't know if this is still active, but, You are kind of my only option right now. So, when I have my 98 blazer in gear or park, and I hit 4 high or low, nothing happens, but, when I put it in neutral, the high and low lights flash, and I can hear a clunking sounds from under my truck. it will go into low, but, not high, and when it is in low, both high and low lights are on. Do you think that is my TCCM? I can hear that clicking. i looked at the wires, and they all seem fine, none are broke, and I checked the wires on the back of my actual switch, and they seem fine. i even checked the fuses that you mentioned earlier...Still nothing...

Kyle's reply;

Hi Jason;

Hmmm... doesn't sound like a TCCM problem... sounds more like an encoder motor problem, or possibly a transfer case problem.

If you hear the clicking of the TCCM, that tells you that the relays are working and are trying to put the encoder motor in gear. There are many reasons for this to happen, broken/leaking vacuum lines to start. The encoder motor wires may be bad. There is a "plastic bushing" that keeps a "fork" in the transfer case in the position (well, the fork keeps the gears in the proper position)... if the plastic bushing is worn, it can cause the transfer case to not switch (this happened to me, but the symptoms were that the system would switch to 4Hi/4Lo, with a big clunk, and it was very difficult to get it back out of 4WD.)

Unfortunately, I can't give you a definitive answer to your problem, but if I had to say, I'd look elsewhere, other than your TCCM (encoder or transfer case)... but then again, I'm not a mechanic either... so I am just guessing! ;)

Good luck!

Regards;
Kyle

Igot a 1999 s10 blazer wont go in 4hi 4lo works and you can hear actutor shift.I have replaced all vacuum lines The vacuum on mine comes off intake to check value then to vacuum switch on transfer case i have 15lbs vacuum at switch. push 4hi button and 4hi&4lo lights flash then it goes back in 2hi Can not hear actutor shift when you push 4hi Thank you Alan

Kyle's reply;

Hi Alan;

Could be a TCCM problem, encoder motor problem or a problem in your transfer case -- all of which has been covered here.

Kyle

I have a 2003 2dr 4x4 Blazer. 2hi works fine, when I press 4hi, both 4hi & 4lo flash & nothing happens. When I push 4lo works fine, front axel engages but when in 4lo & press 4hi it goes back to 2hi.

Kyle's reply;

Could be a TCCM problem, encoder motor problem or a transfer case problem -- all of which has been covered within this thread.

Kyle

Kyle,
I am greatly indebted to you. My new wife's 2000 Blazer lost her 4wd a year ago. SHe found your web site about the TCCM module corrosion, printed off the information and her mechanic fixed it. He was also impressed.
but... this year her dash light 4wd started blinking, (oh Nooo $$$$), and since we are recently married, (happily I add), I took on the task with the help of your web page.
I cleaned the TCCM contacts, then was able to hear it click, but alas, the 4 HI and 4 LO lights flashed when I attempted to engage them. Rats! Step 2, checked all the fuses.. All OK, then found a broken actuator vacume tube broken near the actator itself. Fixed that.. Feeling good with myself now...but no 4wd. AHHH. Step 3...pulled the battery, the acuator was working. Now I'm thinking transfer case may be bad... mega dinaro, (Oh Nooo again)but in the back of my mind I remembered your 30 minute battery disconnect and flip the key 3 times. Voila!!!
We now have 4WD. My wife is impressed with me and my hat is off to you sir. You saved us big time. Will gladly fund your retirement account for what you have saved us. Let me know how.
Bill and very relieved wife Karen.

Kyle's reply;

Hi Bill (and Karen)!

That's a great story! Thanks for sharing that with me... which is all I need! I'm not asking for anything, but hearing stuff like this makes me feel good. Good that I was able to help someone else out... and save you some money in the process.

Hopefully, it also gives others the encouragement / confidence to tackle jobs like this on their own!

Regards;
Kyle

I have a 1992 k1500 blazer (looks like a tahoe) and my 4x4 worked fine until yesterday.Ive read most of your posts. do any of your fixes apply to the 1992 blazer? To engage the 4x4 there is a floor shifter and lights that light up after it warms up. Yesterday the light never came on and no 4 wheel drive. great blog, thanks.

Kyle's reply;

Hi Rich;

It doesn't sound like it's the same type of system, so I'm not really sure what to recommend to you. My system is a purely electronic one (where you push a button, which activates a motor to change modes for you)... yours sounds like a mechanical system where you engage the 4WD manually (floor shifter) and the light comes on simply as an indicator. However, if that was the case, you'd think it would go into 4WD because you're manually putting it there with the floor shifter.

Sorry I can't be of more help.

Regards;
Kyle

Hey, I came across your website while trying to get more information about my 4wd that is not working. My "service 4wd" light is on, but it just came on about 1 week ago. Now I have had this used truck for 3 months now and it has never engaged in 4wd. Now that snow is coming I need to get it fixed NOW!! The indicator lights come on when I start my car but none of them stay illuminated. I had my tccm checked and was told it is good. Any info on what to do next??

Kyle's reply;

As far as I know, if the "Service 4WD" light comes on, there is a problem in the transfer case, or the sensor attached to the transfer case. This can also happen if the sensor gets wet (ie. driving through a deep puddle). Quite a few people report this problem as clearing itself if the vehicle sits for a while (like over night). This is a problem on Silverados, Suburban, Tahoes and Avalanches. ("Control Unit" replacement is reported to solve the problem... I can only assume that "Control Unit" is referring to the TCCM.)

This could or could not be related to your problem, but one thing I can tell you is to get it looked at ASAP. Do a Google search for this problem and you will see that people report that once the sensor produces an error, if it's not looked at, it starts taking out other components of the 4WD system.

Regards;
Kyle

well i brought my truck in and told them they could replace the encoder motor, not sure what was exactly wrong with it, they said it was enguaging only half way then kicking back out. well not sure what could cause this, i asked them to inspect all wires to the tccm and see if the wiring could be the problem, and they said that when they fixed my tccm last year they should have also replaced the encoder motor. They did say they replaced the tccm wiring harness also, so they probaably just ripped me off. Not even caring what was wrong with the actual tccm last year i blew up at the guy and got my encoder motor replaced FREE of charge. guess i should have found out what was wrong with my tccm last year before i got mad? Oh well everything is all good now. But thanks for the advice, next winter when it goes out for the 3rd year in a row, ill at least know where to start looking, haha. Thanks again!!

Kyle's reply;

Free is good! Glad everything is working for you.

I don't know where you are, but around here (Toronto, Ontario, Canada), we're getting dumped on starting tomorrow. 15-25cms (6-10 inches) on Friday and another 10-20cms (4-8 inches) on Sunday. Glad the 4x4 is working! (Actually, I drive a 4WD Nitro now, but my dad still drives the Blazer.)

Just a quick note... if your system only engages half way and kicks out, it can also be caused by "plastic" bushings in the transfer case that wear out. Hopefully, yours is working as it should, and we can write off your problem to the encoder motor. If it happens again (fingers crossed it doesn't), have your transfer case checked.

Regards;
Kyle

The subject field says it all... I put the truck in 4WD and now it won't change back to 2WD....

Suggestions? It's been one thing after another now for 5 years....Im so close to returning it to chevy.... right thru the front window

Kyle's reply;

Yep, you either have a bad TCCM, bad encoder motor, broken vacuum lines, bad actuator or a problem with your transfer case -- all of which has been covered within this thread.

Good luck.

Regards;
Kyle

My 4 wheel drive went out .....is the 92 like the 98's with the fuse problem or is it something totally different

Kyle's reply;

Don't know... when you find out, let me know.

Regards;
Kyle

Wierd problem w/ my 2000 Blazer. Everything is responding perfect in the "electrics" says it shifts to 4H & 4L. worked perfect a week ago... Now it snows, and I'm stuck w/ 2WD. The indicators are working perfect (flash, flash, flash... Solid light!)
The problem is when I try to go up my hill on a snow covered road the only tires that engage are the rear. I can hear the hardware adjust under the truck between 2H, 4H & 4L - but the front axel(s?) doesn't/don't lock in? It did a week ago, when I pulled another car up the street. I'm lucky, because most of my neighbors drive GMs, but it's going to be embarassing if I need a honda civic to pull me up the street this winter.

Thoughts?

Best way to identify/isolate Trans/Case vs. front gearbox?
I read the blog, Not sure if Vacuume line resolution would apply? Electrics seem all in place. Adjustment needed?

Please help me, If you get the resolution I'll pay ya!
(I'm sure you're cheaper than the dealer!)

--Bryce

Kyle's reply;

Hi Bryce;

Sounds like a front diff problem. I'm not sure of the years, but the tranny shop that I had mine at first checked for this problem as it is, apparently, common. There is a gear and a ring that holds it in (if I remember correctly, because it wasn't my problem, so I dismissed it)... the ring breaks and the gear moves out of place. Something to that effect, but I'm not 100%.

If it was the actuator, I'd think the front end would pull to the left... the actuator controls the right front axle only (AFAIK). The left is always engaged with the front diff.

One thing that you can check quickly is to lay down beside the vehicle and have someone SLOWLY drive forward (while in 4WD)... you're looking to see if the driveshaft from the TC to the front diff is actually turning. If it is, the problem is forward of that (ie. front diff), if not, the problem is in the TC.

Regards;
Kyle

PS - Nice to have options with the Polaris though, isn't it! LOL! Just bought myself a 700 x2 Sportsman this year... and glad I put a blade on it! I'm thinking tracks for next year!

I have a 1995 GMC Jimmy, the selector and transfer case work. the front driveline spins but the tires are not engaging. is it the actuator or something else. i have never worked on an electronic 4WD system and so am lost. i have read all of yhe posts but am confused as to what im looking at. any input would be appreciated. thanks

Kyle's reply;

Check the actuator under the battery... the info you need has been posted within this thread.

Regards;
Kyle

Hi Kyle,
I can't thank you enough for this blog. I got a 95 Jimmy on an impound auction for $320. I got it started, and sure enough no 4 wheel drive. I noticed the dash buttons seemed like they didn't click, they lit up when ingnition was turned on, then 2 hi stayed lit, thats all I could get them to do. So I grabed onto the 2 wheel button and gave a little tug and it poped right out of the dash. I went to to local junk yard and got one for $10 and low and behold transfer case locks in, in both HI and LOW. still no 4 wheel yet so I did low tech test on the acuater line (blew into hose) air flowed freely so now I get to fight under a truck. If it wern't for you, I'd still be scratchin' my head becomming even more bald.
THANKS AGAIN,
Rick

Kyle's reply;

Hi Rick;

That's great news! And if you're getting free flowing vacuum, then you know what the problem is... you just have to find it! Good luck with that, and I hope you have a warm garage to do it in! Let me know.

Regards;
Kyle

My wifes blazer last winter (last time we used 4x4) worked fine this winter cant get it to work at all if I push 4 low the tranny shifts into low but no 4x4 and the light just blinks, I hit auto 4 the light just blinks, but I hit 4 high I can hear a small eletric motor at the transfer case turn for about a second but still the light just blinks and when I hit 2 hi coming from 4 hi again I hear the the small eletric motor but if i hit 2 hi from any other blinking light the light just stops blinking and 2 hi lights up. I'm about to check the tccm but seince I here the eletric motor move i dont think its the prolbem any ideas?

ok no corrosion no wetness at all also when i ask it to shift i still here it click at the tccm. Also a new thing I forgot it has to be in nuetral to shift into or out of 4 low when its in nuetral i can also here the small electric motor on the transfer case my next thought is to remove the motor from the transfer case to see if I can shift it maunlly but that involves alot of dissmanlting there's a lot of things in the way is this necessary. If it is I just might wait untill its warmer there has been very little snow in denver area this year.

Kyle's reply;

Hi Scott;

I'm not totally sure what causes the lights to simply blink and then not go into gear. The first time I put the Blazer in 4Hi this winter, it did just that.... I had to put it in neutral for it to go into 4Hi. Since then, it will shift on-the-fly. Why? I don't know. There has to be sensors either in the TC or the encoder motor to let it know when it has reached it's intended mode... I'd suspect it's part of the encoder motor, but I'm just guessing.

Your idea of removing the encoder motor to manually shift it is a good idea, one that I explored and was helpful to me. However, mine was easy... just a couple of bolts and off it came... nothing in the way (mines a little newer and doesn't have the "auto" feature).

I wish I could be of more help, but it sounds like you're on the right track.

Good luck!

Regards;
Kyle

I have a 4WD 2000 BLazer that won't disengage from 4HI. When I press 2HI I can hear the TCCM clicking and the lights flash on 2HI but goes back into 4HI. I also tried 4LO and that does the same thing. However, it does go into Auto 4WD with no problem. I've had the switch on the dash replaced (the letters on the old one wouldn't light up). The vacuum switch on the firewall in fine and so is the vacuum diaphram under the battery. I checked the TCCM the other day and found at least two pins with the infamous corrosion and also corrosion on the female side. I cleaned them off as best as I could. Then I found your blog and read that some wires/connectors could be bad. I will check that tomorrow. Anything else I should consider taking a look at?

Kyle's reply;

Hello confused -- have a look at this post --> http://kylestubbins.com/node/11#comment-2666

Regards;
Kyle

Hi again Kyle,

sure enough the vacume line was bad by the valve cover. I first changed the vacume switch on the transfer case but it was only $16 and I never have to worry about it again. So for $26, and the vast information on this blog, I spent about 2 hours to get it working. Can't thank you enough.

Rick

Kyle's reply;

Hi Rick;

So, for $356 (and a few hours of your time) you got a whole truck WITH working 4WD... not too shabby! ;)

Glad that I could help!

Regards;
Kyle

Hello I wanted to know if you can point me in the right direction. My 4x4 wont work I replaced the switch on the transfercase and the accuator under the battery but still nothing. I thought that I was losing vacuum, just because when I go up a hill my heat if selected to be on the floor vents will change to the top vents the back to the floor/or where ever I have selected them before they changed on there own. This will happen when the rpms go up to or pasted 2000. One other thing can you tell me were I can purchace the cable that goes to the front axle or at least the name. Thank you Edward

Kyle's reply;

Sorry, I don't know the answer to your questions.

Regards;
Kyle

I'm in 4 wheel low, this was after a snowstorm , we never have used the 4 wd before.
I have change the dash selector, checked out the tccm module it clicks but will not come out of lo 4 wheel drive, I disconnected the vaccume module in the center of the fire wall.

Still it shows in "four wheel low" I feel my next move is removing the front drive shaft , and pulling the servo shift motor on the transmission , it looks as if the are around 9 wires going to that servo motor, I'm I on the right tranck ? or should I test other things? I have tried to reset the computer, also stood on one foot and jumped around three times " that didn't help either" !!!

I would love your input if I may ask?

Randy

Kyle's reply;

Hello Randy -- have a look at this post --> http://kylestubbins.com/node/11#comment-2666

Regards;
Kyle

i have replaced the gear and spring and fork in my blazer the gear was ground up about a yaer ago now i have the same problem could this be a bad transfer case vaccume switch no leting the gaer fully engauge ????thanks scott

Kyle's reply;

Hello Scott;

Unfortunately, I have no idea -- I am not a mechanic.

Regards;
Kyle

I have a 2002 Chevy K1500 that has a problems with the 4-wheel drive system. Initially it wouldn't disengage the 4WD in the front differential. With a little advice from the local service garage I replaced the electronic actuator as well as the swith for the dash. It goes into 4WD but wont disengage unless I crawl underneath and unhook things to back it out manually. The lights for the dash switch will not illuminate 2WD,4WD-high or low now. Before replacing the switch in the dash it was getting stuck with 2WD & 4WD indicator lights illuminated after I put it into 4WD high. I still had to disengage the 4WD in the front differential manually. Is there anything else I can check before buying the expensive module for the 4WD?

Kyle's reply;

As I have stated many times within the three pages of this post... everything that I know about the Chevy 4WD system has been posted here. I have no further information to offer. I am NOT a mechanic.

Regards;
Kyle

I am working on a 1999 jimmy .I have read your page but have not solved my problem yet so I need your help .The lights on the buttons do not light up at all to show 2hi and nothing happens when you push any of the buttons . When you first turn the ignition on all the lights will light up together for a second then they go out and are NEVER seen again . I pull the TCCM but it and the plug and prongs look new .I then checked with a test light and found power at the button panel and the TCCM . Any help would be great !THANKS

Kyle reply;

Well, I guess it's time to close down the comments again... people just don't get it...