First off great site lots of great info. Heres my problem. The other day I tried to shift from 2h to 4h. When I did this the 2h light stayed solid and the 4h light blinked then also stayed on solid and my 4wd service light came on. I stopped and when I restarted now I have the service 4wd light and no light on the selector dial. I disconnected the battery for 10 min to reset the computers but, that didnt help. After reading several posts it seems I have a bad TCCM. I have seen several on ebay and in junk yards for under 100.00. My question is do we all agree this is the problem and if so, can I get any one I see listed and is it just a plug in and away we go or will it need to be programmed. Thanks for your help
4WD Problems
- Thread starter tkattre
- Start date
Can you answer if you have done all the steps outlined on this document?
Just so we know where we are starting from.
Offroadtb.com Diagnosing the 4WD System
Just so we know where we are starting from.
Offroadtb.com Diagnosing the 4WD System
Welcome! Could you fill out your profile so we know what options you have and the year? Especially if it's a 2002, you have the notoriously flaky TCCM. If you buy one that had been used previously in a TB or Envoy, no dealer visit will be necessary. Make SURE it's from a 2003+.
Only time you need a dealer reflash is if you buy a virgin new one from a GM supplier.
Dorman is reputed to make aftermarket new ones that don't need programming, that you can get from your local parts store.
You could also have congealed grease in the front axle actuator, and slow engagement is enough to piss off the TCCM and light up the Service 4WD dash lamp. But that's not confirmed to be your problem when all the switch lights go off.
Also can you share your mileage and do you have maintenance records showing the transfer case fluid has been changed as required every 50K? Vitally important.
Only time you need a dealer reflash is if you buy a virgin new one from a GM supplier.
Dorman is reputed to make aftermarket new ones that don't need programming, that you can get from your local parts store.
You could also have congealed grease in the front axle actuator, and slow engagement is enough to piss off the TCCM and light up the Service 4WD dash lamp. But that's not confirmed to be your problem when all the switch lights go off.
Also can you share your mileage and do you have maintenance records showing the transfer case fluid has been changed as required every 50K? Vitally important.
Sorry about that it is an 05 ext with 95,000 miles on it. I did change the transfer case fluid at about 65,000 with gm auto trak fluid.All of the fuses look good. I kind of used fishsticks thread to help come to my conclusion about the tccm. When I try to switch it into 4wd I dont hear anything from the motors under the vehicle. Thanks
You can pull just one fuse for 30 seconds to reset the TCCM. It's a bit riskier to pull the battery cable. If you do that, then try a one-step transition like 2HI->A4WD, not the two-mode jump from 2HI->4HI. Does the behavior change?
I have also pulled fuse #8 under the hood just to check if it was blown. It was good. When I turn the key to acc all 4 lights come on for a second I assume to test the lamps. Then they all go out. I have tried just going 1 over to awd but, I get the same thing no motor operation and no lights. It seems to me either the switch isnt telling the module to activate 4wd or the module isnt sending the signal the the various motors to activate. I was thinking the switch was ok because the test lights come on when the key is turned.
The lamp test part of the switch is totally separate from the mode selection part of it. As IllogicTC posted - the exact behavior of the motor noises and lamps in each and every mode change is critical to troubleshooting. If you had a local buddy to swap parts with for troubleshooting it could go faster.
Yes I totally agree I also wish I knew someone close with a tb I could swap modules. To answer your question at on all 4 lights are on for a few seconds then all four go out and never come back until I turn the ignition switch off and back on.
A mechanic with a GM Tech II tool could diagnose it in a minute by seeing if the issue is that the TCCM isn't working, or if it's working, but the actuator or encoder motor fails a diagnostic. But that would cost as much as an Ebay TCCM. Hard to say if shotgunning would cost you less than paying for a diagnostic. But personally, I'd start with a TCCM.
Thats kind of what I thought too. I called a few local salvage yards and can pick one up for 40.00. I have to take it out but seems very easy to do. I have to wait a few days for the temps to warm up since I have to pull it myself and our highs are supposed to be less than 10 for a few days, it is working fine in 2wd for now. I will let you know the result. Thanks
One last question. If the actuator or encoder were bad after start up would they kill all of the lights on the switch like that or not? The reason I am second guessing myself now is when I called the junk yard today he talked me out of buying the tccm because he said he never sells them the problem is usually with the actuator.
Robbabob
Member
- Dec 10, 2012
- 1,096
For $40.00, buy the TCCM and go from there. Everything sounds like it's the issue.
No salvage yard is going to know these trucks better than the advice you're getting from these folks. Nobody said 100% for the cure, but it's the cheap start that probably fixes 80% of what you describe.
No salvage yard is going to know these trucks better than the advice you're getting from these folks. Nobody said 100% for the cure, but it's the cheap start that probably fixes 80% of what you describe.
I think if a motor was bad, when you asked it to change from 2HI->A4WD, the light on the new mode would flash, then it would fall back to lighting up the 2HI mode light, and the "Service 4WD" light would come on in the dash. The mode lights on the switch would not all go dark, unless the fault was TCCM-related. You should also try to run the system with the engine off, and you can hear the two motors better. Have you tried that?tkattre said:
2HI->A4WD mode transition: You hear the front actuator - a high pitched noise for just over one second. AND a lower pitched short noise from the transfer case encoder motor.
A4WD->4HI: Just a short noise from the encoder motor
4HI->4LO (in neutral): A medium length noise from the coder motor accompanied by (sometimes) a little lurch or clang.
Well today I went out and picked up the tccm. It is from an 04 trailblazer the pn on is 12584313 I assume it is a replacement part since the pn on my 05 is 12590220 it sounds like they are all interchangeable as long as it is out a 4X4 not an awd only (bravada). I have the same problem when I turn the ingition key to acc all 4 of the switch lights come on for a few seconds then all 4 go off. I cant hear any noise when I switch from 2hi to awd or 2hi to 4wd. I was by myself so, I couldnt crawl under the vehicle to get right next to it. I was sure it was the tccm and using a used module you can never be sure either I guess I wish I know someone with a tb to test it in. I think I am going to order the switch and front actuator to see if either of these will solve the problem. At this point shotgunning is my only option.Let me know what you guys think.
One guy on trailvoy said his problem was only fixed after he paid somebody with a GM Tech II tool to run a thorough diagnosis and the bad part nobody ever thought of was the VSS (speed sensor) on the transfer case. Since there are three VSS on the TC (one for the front prop shaft, two on the rear driveshaft - one used by the TCCM and the other one used by the PCM to obtain the vehicle's ground speed for the speedometer and shifting commands), that was an unexpected fault I totally forgot about until a quick search just now.
Are all 3 vss sensors the same? I ordered 1 of those and the sel switch. I cant see either of the 2 motors causing a no light condition either. Do those sensors have to be screwed in to the tc to test or can I just plug it in and let hang to test, that way if it isnt the problem I can return it.
All three are the same. Since the system works with zero forward velocity, it should test out just fine with the sensor out of the tailpiece. Nobody really knows which of the two is for the TCCM, however. And the problem may be in the wiring harness, not the sensor. Some folks kick up rocks or ice that damage wiring under there.
I will wait until I get that equip and let you know the results. Its kind of hard to look real close at the wiring with all the snow and road salt. If this doesnt do it I might have to pay the 100.00 diag fee the shops want to hook it up and check codes. I assume driving the vehicle like this is doing no more damage, it is just running in 2wd and I dont have access to 4wd right now. I jacked up the front and the wheels spin independently like they would in 2wd
Here is an update. I got a used Encoder and TCCM. New actuator new 4wd switch and new vss. Today I was determined to solve my problem. When I started I had no lights on the 4wd switch,, the service 4wd light was on and no motor operation when I turn the dial. I tried the tccm no change. Then I put on the encoder on( not installed just hanging) and when I turned the switch to acc the light came on on the switch and no service 4wd light.I went to awd the encoder just hummed and I heard the actuator move. The light on the switch went to awd like normal. Then I went to 4hi the actuator didnt move but the encoder move counterclockwise 1/8 of a turn or so. That was it, when I moved the switch back to 2 hi nothing moved and when turned the ignition off and back on I was back to the same orig problem no lights on the 4wd switch and the service 4wd light was on. I tried hooking up the new actuator and switch but, no change. I took the old encoder off of the transfer case to look at it. Are those encoder motors spring loaded or not, when I took it off it sounded like it was. The status the encoder was in there was no way it would match up to the shaft on the transfer case so, I took the top off of the old encoder and turned the motor counterclockwise to line up the indentation on the motor and tc shaft. When I did this and reinstalled it on the tc I turned the ignition to acc and I had my light back on the 4wd switch and no service light. When I tried the modes on the 4wd switch it was back to the same problem as above. My question is where should the indentation be on the encoder motor at the various stages and how far should the shaft turn on the transfer case for me I could only turn it approx 1/4 or less. Sorry about the long winded response but I am not sure what to try next and am trying to figure what the normal modes are for the motor. Thanks for your help
I went back out last night to try a few more things to see if I could eliminate the transfer case or front disconnect. I should be able to connect but not install a new actuator and encoder and cycle through the various 4wd modes and see the motors move, is that correct?
With the encoder hanging and the indentation on the motor shaft at the 12:00 position towards the wiring. When I go from 2hi to awd everything is fine the encoder turns about 1/8 turn counterclockwise the actuator locks in the front diff. When I go back to 2hi everything works ok there too the actuator unlocks the front and the encoder goes back to the 12:00 position. Then when I go 2hi to awd it works ok but when I go from awd to 4hi the encoder goes another 1/8 counter clockwise and my service 4wd light comes on and that is it until I unplug the fuse and manually turn the encoder back to the 12:00 position then I can start all over again. I purchased the encoder used does this sound like that could still be the problem or wiring. I checked the plug to the encoder and that is good. Why wont the encoder reset back to the 12:00 by itself? Sorry to be a pain but this is becoming a mission to find out what is going on!!! Thanks for your help
Have you found a solution to your problem? I have gone through most solutions. I am as far as a new encoder motor and a junk yard TCCM. The encoder took the light off for 2 clicks of the 4x4 dial but nothing more. TCCM did nothing at all. I am stumped. I may just have to check the transfer case fluid level. I just want to do it on my own without hitting the shop.
jballentine
Member
- Dec 24, 2011
- 44
I just took apart my disconnect cleaned all parts inside, replaced bearings and seals. Put it back on the truck engaged 4 high but I could still spin the half axle by hand. So I bought a new actuator put that on tried it again still spin the axle by hand I can feel the gears but they just aren't meshing. I used a socket and pushed it in and got it to lock in that way. Could use a little help what to do next. Take it all back apart??
Sometimes you can put in so much grease that the actuator has a hard time pushing in as far as you can by hand. Exercise it many times by hand then try the actuator again. Or the fork is worn and won't slide the splined collar onto the gears enough to lock them together.
jballentine
Member
- Dec 24, 2011
- 44
Thanks, I will cycle it again a few times by hand. I guess if I have to crack it back open it won't be that hard I only went as far as getting the axle shaft back in and testing first. Better than getting it completely together and take all the way back apart. Got any idea of the specs of the fork? Or maybe just take the fork to auto parts place and compare them?
Don't think anybody but GM sells the internal bits. And many times, GM sells out of some of them. Hence the availability of two aftermarket suppliers.
jballentine
Member
- Dec 24, 2011
- 44
I'm leaning toward the fork is worn as well. I pumped it by hand a few times tried the actuator again & nothing. I took it back off the pan pumped on it some more it kinda feels a little sloppy, not that I know what a brand new one feels like pumping by hand to engage. Figure what the heck I'm this far already it won't hurt to change to fork & spring as well.
jballentine
Member
- Dec 24, 2011
- 44
I was also on the off-road forum reading as well. When I pushed the fork in by hand forcing the gears to connect I was turning the passenger axle I looked under at the prop shaft it was turning. Have I lost the front diff as well?
No. If the prop shaft is turning then the disconnect is engaged. I thought you were supposed to have the transfer case in 4HI, and the engine off, and the front tires in the air. Then the front driveshaft will be held from turning by the transfer case.
What exactly is the state of the vehicle when you're doing these tests?
What exactly is the state of the vehicle when you're doing these tests?
jballentine
Member
- Dec 24, 2011
- 44
Yeah I though about that after I posted. Front tire, axle & disconnect are currently off. It was not switched to 4 high like it should have been. I was just pushing it by hand there a few times before trying the actuator again, just decided to look under the truck.
jballentine
Member
- Dec 24, 2011
- 44
jballentine
Member
- Dec 24, 2011
- 44
Any chance you took pics to show the extent of the fork wear or distortion? Assume you kept the old one as a trophy?
jballentine
Member
- Dec 24, 2011
- 44
No I didn't take any pics. I do still have the fork as a trophy. When I was cycling the old fork by hand it was just extremely hard to cycle it. New fork in it cycled real easy, I don't know how much it was distorted I compared the old to the new. The part that I think was off is the pin going in the spring it felt like it was catching on the housing before replacing it.
I pull wishbones with Mrs. Roadie often. What I usually wish for, is never going to be delivered by me to any guy on the forum. Trust me.IllogicTC said:I've heard that if you take your shift fork and you and a friend pull on opposite tangs, whoever gets the spring is granted a wish by The Roadie.
