ok i have a 2001 gmc jimmy with a 4 button 4wd. my problem is ill be driving down the road and ill put it into 4wd and it will go in and everything and a couple seconds later my service 4wd light will come on. i will push the 2hi button to try and put it back into 2wd and nothing happens. if it turn my truck off and start it back up i can put it back into 2wd. then if i put it back into 4wd the service 4wd light will come on again until i turn my truck off and restart it. what is going on?????
2001 gmc jimmy 4wd problem?
- Thread starter Joe
- Start date
Molson02536
New member
Inspect your TCCM (Transfer Case Control Module) and wire harness. It's located behind the kicker panel on the passenger side, once you have the kicker panel off you can see the TCCM and the wire harness and it's common for corrosion to damage the harness causing a faulty connection. Clean up any corrosion and repair any damages and loose connections.
There is also, what is called an "encoder module", on the side of the transfer case that controls which mode you are in (2, 4HI, 4LO) -- if water got in there and froze, it could be preventing the encoder from changing modes. The encoder motor could also be bad. Anyway, if worse comes to worst, you can unscrew the encoder module and manually shift the transfer case into any mode you wish. Unfortunately, I can't tell you which way is which -- you'll have to figure that out with trial and error! Don't worry, you can't hurt anything -- you'll either be in 2 wheel drive, or one of the 4 wheel ranges. If it's not 2 wheel, try again until it is! (There will be metal "tab", for lack of better words to describe it, sticking out of the transfer case -- put a wrench on it and it should move with minimal effort. NEVER FORCE ANYTHING! Take it for a drive and see what you're in. Hopefully, you'll get it on the first try!
Without knowing what is going on with your controls, I don't know what more I can offer. If your controls work, and you here the Transfer Case Control Module (TCCM - the module under the passengers kick panel!) "click-click", then it's working -- have someone do that while you listen under the vehicle for the encoder motor. If you hear that, then you have issues further along the system, such as the servo or actuator (vacuum operated, located under the battery).
You could also unplug the TCCM and tap on the encoder module to see if it may just be stuck (a warm garage wouldn't hurt either!) -- leave the TCCM unplugged for at least 2 minutes, then plug it back in. Then, turn the key on to off 5 times, then to on and try it.
You may also look for a friend, or mechanic, that can read your DTC's (Diagnostic Trouble Codes). I do not know what kind of problem you are having, but let's assume that you have dash lights and the light DOES go to the 4x4 high (or low) position -- at this point, listen to see whether or not you hear a definitive "click-click" coming from the TCCM. If you DO NOT hear the "click-click", you have a bad relay in the TCCM. The good news -- you can get a replacement relay at your local electronics store and replace it in the TCCM. You will need a soldering iron and some basic electronics skills, but it is very easily achieved (a couple of points to unsolder and then re-solder the new relay in place).
Now, if you DO hear the "click-click", then your TCCM is working and trying to shift into 4WD -- the problem, would then be with the module that is actually on the transfer case (encoder motor) -- it is a simple "motor" setup that simply moves the transfer case gears to the proper mode.
Hopefully, this will give you something to start with. Let me know how you make out, or if I can answer any other questions.
Good luck and keep us all posted.
