I have a 2002 GMC Envoy that locked into 4wd a few mnths ago and would not unlock. So the first thing I was told was change the selector switch. Did that and nothing happened. Then learned the transfer case motor was bad. Replaced it and it kicked back to 2wd, it made the "service 4wd light" come on the dash and I cant get any other option on the selector, it actually lights up all four options when I start the Envoy then all the lighted dots go blank and the vehicle stays in 2wd. I just bought a transfer case switch, but dont know where it goes. Any help or direction would be really appreciated.
2002 Envoy 4wd not working
- Thread starter GoFasTA
- Start date
Molson02536
New member
The TCCM may be in sleep mode so try pulling the fuse for a min and placing it back in the fuse box to your TCCM #8 i believe, with your ignition switch to the on position. This should wake up your TCCM, if it does not work, there's a service report out there for reprogramming the transfer case at the dealer.
Good luck and keep us posted.
Good luck and keep us posted.
Thanks Molson. I gave it a try, but still does the same thing. I guess Im one of the lucky ones that has to take it to the dealership to be reprogrammed. I just wanted to do all I could before having to go to that step. Thanks again for the help!
Molson, I took my envoy to the dealership and they said they could not communicate with the TCCM. They said the 2002 model has to be replaced then reprogrammed. I dont think thats correct. Do you know where that service report for the dealer is? or could you give me any insight on this please.
Molson02536
New member
Check the main fuse #8 under the hood first. If OK, the TCCM might be having problems waking up, especially 2002-2003 units. In that case, turn the ignition to RUN to wake the vehicle up, THEN pull, then reinsert fuse #8 after ten seconds to reset the TCCM. If the switch indicator lights come on then, then you have the sleepy TCCM syndrome.
For fun also, try to put the system into NEUTRAL mode. Check the Owner's Manual if you don't do this often. The NEUTRAL lamp is run off a different circuit than the other mode lights, in case it's a lamp issue instead of a TCCM problem.
Also check fuse #48 under the rear seat - it runs the front axle actuator, which if it fails will also disable the TCCM and make it give up.
How it works. The actuator engages the front axle with a 2WD->A4WD mode change. The encoder motor ALSO moves to get the transfer case clutches READY and in position to transfer torque if it detects wheel slippage. But the encoder motor moves a bit to be ready, and makes a distinctive noise, lower pitched (larger motor) than the actuator.
When you change from A4WD->4HI, the encoder motor moves a bit more to fully engage the clutches. THIS movement is similar to what it does if it detects wheel slippage. But the high-pitched whine of the front axle actuator isn't present on an A4WD->4HI transition because it's already engaged. (If it's working, that is.)
Everybody should try this in their driveways TODAY. In case the system fails later, you need to know what it sounds like then it's working. Much faster troubleshooting than taking it to a tech tool for $$$ diagnostics.
THE ROOSTER
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TCCM shifting on it's own
My 02 Envoy when going OUT of A4WD will shift to neutral once the vehicle has stopped or coasting. My wife put it in A4WD during Friday's snow, today put it back into 2WD and when I parked at Kroger it was in 4LO when I left. Usually it shifts to neutral so I was surprised to see it in 4LO, only way to get it going is to put selector in A4WD until I get home and reset the TCCM.
THANKS SO MUCH FOR FORUMS LIKE THIS
My 02 Envoy when going OUT of A4WD will shift to neutral once the vehicle has stopped or coasting. My wife put it in A4WD during Friday's snow, today put it back into 2WD and when I parked at Kroger it was in 4LO when I left. Usually it shifts to neutral so I was surprised to see it in 4LO, only way to get it going is to put selector in A4WD until I get home and reset the TCCM.
THANKS SO MUCH FOR FORUMS LIKE THIS
Strange way I finally got 4 wheel drive to engage on my 02 Envoy....I lost 4 wheel drive a wile back so I replaced dash switch, didn't work, replaced actuator and stil nothing.i ended up pulling the #8 fuse wile ignition was on and then put back in after 10 seconds.switch lights came back on but stil no engagement but got it to engage by turning dash switch to 4hi wile ignition was off then turned ignition on,off,on,off and then back on and it actually worked and 4wheel drive engaged lol and to get it back out of 4wheel I had to do the same by either putting it in neutral, turn switch back to 2 wheel then turn ignition off, on,off then start vehicle then it would disengage lol.i don't know why this worked but it's been working this way ever since.Hope this helps someone
Hi Kickstart, I turned ignition to on,opened the hood and in the fuse box I just pulled the number 8 fuse out, waited ten seconds or so and stuck fuse back in then went back and turned ignition back off then on again and the lights lit back up and then back out. Once you put dash switch to 4 hi and turn ignition on,off,on,off and then start vehicle the 4hi light should stay on.
Correction on 4 wheel drive dash lights
Put switch to 4hi before resetting #8 fuse and make sure ignition is in on position.once fuse is reset turn ignition off then on a couple of times before starting vehicle . The 4hi light will light up then go back out but it should now be engaged into 4 wheel. To see if actually engaged you can turn switch to2wheel, turn off vehicle then turn ignition back on and off a couple time stand you should hear and feel it disengage.
Put switch to 4hi before resetting #8 fuse and make sure ignition is in on position.once fuse is reset turn ignition off then on a couple of times before starting vehicle . The 4hi light will light up then go back out but it should now be engaged into 4 wheel. To see if actually engaged you can turn switch to2wheel, turn off vehicle then turn ignition back on and off a couple time stand you should hear and feel it disengage.
G
G-811448
02 GMC Envoy 4x4 The TCM when the Battery Is Dead or un plugged the Transfrer Case Module has to be Reprogrammed !