4WD Auto-Engaging?

woyster_00z71 · November 27, 2003

Prolem has happened twice now. First time was about a week or so ago when I was driving through the parking garage at work and turned around the corner. The truck started lunging wierdly and tires were chirping. I didn't know what the problem was. Second time was just a few days ago. I had started the truck and it idled for about 5 minutes. Then I put it in gear and backed up turning right. As I turned the wheel back to the left and pulled forward I realized the transfer case was engaged and the tires were once again chirping and the truck was lunging. Then I heard/felt the transfer case disengage. During this time, the 4WD light on the autotrac was on 2WD.

So, any ideas? I am going to make an appointment to take it to the dealer next week but I would like to have some knowledge of the problem before taking it to them that way if they give me the run around I have some information to back me up.

Thanks guys,

B.J.

Shaners · November 28, 2003

There is definatly something wrong... Either with the switch or T-case.

If it is the T-case I hope you have some warrenty left...

chevroletmb · November 28, 2003

i agree

sounds like a switch or the t-case encoder motor

the switches are know to fail so i would start there

encoder motors are expensive so good luck

woyster_00z71 · November 28, 2003

Thanks guys. Yes, I do have warranty. I bought a GM-Protection Plan warranty when I bought the truck back in March. I am going to try to remember to call and make an appointment tomorrow to take it in.

Thanks again,

B.J.

GreenZ71 · November 28, 2003

The switch is a common failure. Mine started acting up around 40k miles. I couldn't switch it from 2 wheel into any other mode. When it finally did go into 4 it would randomly switch back to 2. I changed the switch and it works fine now.

Markeaux · November 28, 2003

Your failure is different, but just fyi A few weeks ago my 01 Tahoe started throwing a "Service 4wd" message. I scanned for obdii codes and there was one that my Helm service manual said was indicating a bad switch module. So ordered one from gmpartsdirect.com for $32 (Part#: 15709327); but, haven't put it in yet (actually the message has not reappeared after a few power off cycles, but that switch assembly is known for failing so am going to go ahead and replace it soon). I, too, have the GMPP but I would have had to miss work which would have cost me way more than me just getting+installing the switch myself.

Shaners · December 1, 2003

If your rear differential is locked up, then you will definatly have trouble going around tight corners.

woyster_00z71 · December 1, 2003

Well, it has done it one other time now. But I now think it is the rear differential instead. It feels like the diff is locking up. I just talked to the service manager at the dealership and he agrees that is sounds like the differential is locking up. The first time was in the parking garage after going around several right hand turns. He said something about the clutch packs and turning the same direction that you can feel the diff disengaging. I don't know why it engaged in the first place. The other two times were backing out of the fire station parking lot after responding to a call. Both times I came screeching to a halt in the parking lot and I guess the diff had locked up. The road was wet both times and I did have some wheelspin on the way into the parking lot. So I can see that the diff could be locked up and it has to move some to unlock.

Does this sound like a legitimate explanation? Thanks.