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.

 

[YukonRog]

From the shop manual:

View attachment 348833

View attachment 348834

Gotta love them ' lectronics!

 

[Fless]

The code points to the actuator on the transfer case ("lock circuit" is the clue), not the front diff actuator, and @swathdiver posted a diag path in post #2. Not to be rude but if you're not willing to, or capable of, following that simple procedure with a DVOM then it's time to fire up the parts cannon or take it to a reputable shop to have diagnosed and possibly repaired.

 

[Fubar0715]

Am I the only person who gets annoyed with users without a location in their profile. Just an observation but I feel like if that was info we collectively had, maybe could refer the user to a shop or someone local to them...

 

[Doubeleive]

The code points to the actuator on the transfer case ("lock circuit" is the clue), not the front diff actuator, and @swathdiver posted a diag path in post #2. Not to be rude but if you're not willing to, or capable of, following that simple procedure with a DVOM then it's time to fire up the parts cannon or take it to a reputable shop to have diagnosed and possibly repaired.

ya I wasn't paying attention, that one can go out too

 

[George B]

The code points to the actuator on the transfer case ("lock circuit" is the clue), not the front diff actuator, and @swathdiver posted a diag path in post #2. Not to be rude but if you're not willing to, or capable of, following that simple procedure with a DVOM then it's time to fire up the parts cannon or take it to a reputable shop to have diagnosed and possibly repaired.

Sorry, I missed that when I responded. I agree with you that the OP should use the information already provided to help diagnose or rule something out.

 

[UpAndDown]

Fless and Fuvar0715 thank you for your replies. Fless are you saying the issue is in the encoder motor assembly? I am confused with the order of operation so I am getting hung up on if the issue is with the encoder motor, the transfer case control module, or the selector switch. If you’re feeling is that it’s the motor assembly then I will go with your educated guess and I appreciate you sharing the knowledge. Fubar0715 I am located in just west of Boston. Not sure how to add that into my profile but I will look into it. Thanks again for all of the info and if anyone else has anything to add, please post. Thanks again.

 

[YukonRog]

Am I the only person who gets annoyed with users without a location in their profile. Just an observation but I feel like if that was info we collectively had, maybe could refer the user to a shop or someone local to them...

Witness Protection Program. Anonymity....

 

[Fubar0715]

Ah, forgot about WitSec....spies like us!!! lol

 

[Fubar0715]

Fless and Fuvar0715 thank you for your replies. Fless are you saying the issue is in the encoder motor assembly? I am confused with the order of operation so I am getting hung up on if the issue is with the encoder motor, the transfer case control module, or the selector switch. If you’re feeling is that it’s the motor assembly then I will go with your educated guess and I appreciate you sharing the knowledge. Fubar0715 I am located in just west of Boston. Not sure how to add that into my profile but I will look into it. Thanks again for all of the info and if anyone else has anything to add, please post. Thanks again.

There are 2 of us in the NE area that have Tech2 devices...both of us are very green in the use but we have one. Both us are in Southern New Hampshire.

 

[TollKeeper]

Not sure how to add that into my profile but I will look into it. Thanks again for all of the info and if anyone else has anything to add, please post. Thanks again.

Click on your Forum name in the top right corner of your screen if you are on a computer. Scroll down, fill in the info, click save, done.