Stuck in 4WD

[UpAndDown]

So bought an 08 Tahoe LT 4WD 5.3 in June. I have a work tuck so I use the Tahoe only occasionally. When I bought it, it had a “service 4wd system” message and an associated C0321 code. Today when I was driving it I felt something weird when going around a corner along with a whine. I then noticed that the indicator light for 4H was lit even though the selector knob was in 2WD. I tried cycling into 4H then AUTO then 2WD and it will not go into 2WD, only to AUTO but it’s still really in 4H even thigh the selector says AUTO. It won’t choose 2WD. Is there a way to get it to go into, and hopefully stay in, 2WD until I can get around to troubleshooting and fixing it? I didn’t try cycling all the way to 4L or N as I didn’t want it to get stuck in one of those modes. Any replies are appreciated. Thank you.

 

[swathdiver]

So bought an 08 Tahoe LT 4WD 5.3 in June. I have a work tuck so I use the Tahoe only occasionally. When I bought it, it had a “service 4wd system” message and an associated C0321 code. Today when I was driving it I felt something weird when going around a corner along with a whine. I then noticed that the indicator light for 4H was lit even though the selector knob was in 2WD. I tried cycling into 4H then AUTO then 2WD and it will not go into 2WD, only to AUTO but it’s still really in 4H even thigh the selector says AUTO. It won’t choose 2WD. Is there a way to get it to go into, and hopefully stay in, 2WD until I can get around to troubleshooting and fixing it? I didn’t try cycling all the way to 4L or N as I didn’t want it to get stuck in one of those modes. Any replies are appreciated. Thank you.

From the shop manual:

 

[UpAndDown]

 

[UpAndDown]

Thanks for the info. Still confusing as to what I should test and how.

 

[wsteele]

It is likely the transfer case actuator (tc motor) or the transfer case control module. Both require some work with the Tech 2 or other high end scan tool (like a Snap On) to complete the repair.

If you are near anyone listed in the Tech 2 owners sticky above, maybe reach out and see if they may be able to help with that side of things, then just do the diagnostics listed in @swathdiver’s post above.

if you still don’t know what to do, take it to a dealer, it will be a fairly expensive repair, like $500-$1200, depending on if it is the motor or the tccm.

 

[UpAndDown]

Thanks wsteele. Does the fact that if I move the dial between 2HI, AUTO and 4HI I can get the light to go between AUTO and 4HI when I am on those respective positions but never into 2HI provide any clue as to which component is bad? Also, even though the light switches between AUTO and 4HI when each is chosen, there is no actual movement of anything in the transfer case. I am leary of trying the 4LO or N positions as if it does move into either of those and then not able to move out of it, I am in a worse position than I am now. Thanks again for any replies.

 

[wsteele]

Thanks wsteele. Does the fact that if I move the dial between 2HI, AUTO and 4HI I can get the light to go between AUTO and 4HI when I am on those respective positions but never into 2HI provide any clue as to which component is bad? Also, even though the light switches between AUTO and 4HI when each is chosen, there is no actual movement of anything in the transfer case. I am leary of trying the 4LO or N positions as if it does move into either of those and then not able to move out of it, I am in a worse position than I am now. Thanks again for any replies.

I am not familiar enough with how the systems work to be able to hazard a guess. I had a TCCM go bad early into new truck ownership on my 07. I think it was in "Auto" when it happened, but ended up in 4L and was stuck there. Being the superstitious type, I now only use 2H, 4H and 4L and never Auto.

 

[UpAndDown]

I have no access to anyone with a Tech 2 locally without paying a garage. I’m just trying to rationalize this problem logically. The fact that I can turn my selector knob between 2HI, AUTO and 4HI but the light only toggles between AUTO and 4HI, with no response at all, not even a flashing light as if it’s trying, when I select 2HI has me wondering if it’s either the selector knob itself or the TCCM. If it were the encoder motor wouldn’t it at least flash the light on the 2HI position on the knob and then “time out” if it didn’t shift and go solid on the position it is actually in? I’m not sure what control what or the sequence of operation here but this seems logical to me. Does anyone have any thoughts? I’d love to hear anything you guys have to say. Thanks again.

 

[89Suburban]

Sub'd

 

[George B]

@UpAndDown
Your logic above sounds correct. I would suspect the control module since you get no response as described. I had a similar failure once in the past. I would still suggest trying to gain access to a tech2 for diagnostics. Maybe time to pick one up. A trip to the dealer for this problem will cost you the same in labor.