"service 4-wheel drive" on dash when key is turned on.

[Bigfish95971]

Service 4x4 light has been comping on for some time. Now it won't switch to anything else, Has stayed and run in 2x4. Lights on switch all flash during key boot up. Fuse good. What is my likely problem, switch, shift motor, wires, other? No codes.

 

[Scottydoggs]

your going to need to get it scanned with a good scanner, like one a shop has, the cheap P code readers wont pull up C and U codes. the code tells you where to look first so your not tossing the parts cannon at it and wasting money.

 

[Fless]

your going to need to get it scanned with a good scanner, like one a shop has, the cheap P code readers wont pull up C and U codes. the code tells you where to look first so your not tossing the parts cannon at it and wasting money.

That's right -- I'll likely be a Cxxxx code.

 

[Run4st]

You probably already fixed ...Just in case...I have seen transfer case motor kick that light on it...mine is starting to do this. I was told by reliable mechanic who has owned 5 of this gen veh that he has seen this multiple times. Doesn't look like a bad fix to do.

 

[Run4st]

You probably already fixed ...Just in case...I have seen transfer case (decoder) motor kick that light on it...mine is starting to do this. I was told by reliable mechanic who has owned 5 of this gen vet that he has seen this multiple times. Doesn't look like a bad fix to do.

 

[Fless]

You probably already fixed ...Just in case...I have seen transfer case (decoder) motor kick that light on it...mine is starting to do this. I was told by reliable mechanic who has owned 5 of this gen vet that he has seen this multiple times. Doesn't look like a bad fix to do.

It's called an encoder motor, but there's no guarantee that's the issue. Best to get the code to see if it takes you in that direction.

The internal transfer case range position sensor can be replaced, instead of the entire encoder motor.

 

[Run4st]

Would be interesting to see what Code and outcome was on this.

 

[PatL]

I have had 2 issues over the years re: the 4WD on my 2003 Tahoe.
1) The "service 4WD " notice has come on probably 20 times over the years since I owned it, staring in 2004 after I bought it. I pull the fuse, wait a few seconds, and then put it back in and all is well. This is a programming issue that probably got corrected in some update but I am not going to pay the dealer to do an update that is this easy to resolve.
2) The encoder motor that others have mentioned needed to be replaced as the encoder contacts wear out, even though I rarely change it out of 2WD. Just a bad design. Pretty easy to do yourself.

Hope this is helpful

 

[PNWYukon]

Had the same issue, so I shifted into 4wd and out and back in again and it stopped. Periodically shifting in and out of 4wd seems to keep it happy.

 

[Fless]

Would be interesting to see what Code and outcome was on this.

Unfortunately the OP hasn't been back here since the thread was started.

 

[Bigfish95971]

Sorry been busy hunting. not fixed yet. Got several code I do not remember except they indicated the tccm not communicating. Doing reset right now. Not confident. Is a used TCCM plug and play? I have not read of any programming required on new or used.

 

[rockola1971]

Rarely does the encoder motor itself fail. Its more likely the commutator or as GM calls Range Position Sensor is worn. The RPS can be replaced by fairly easy partial disassembly of the Shift motor which GM also calls the Encoder Motor (Its a DC motor). The RPS is what tells the TCCM (Transfer Case Control Module) what position the Tcase is in. If the TCCM doesnt know because of a dirty commutator/worn commutator then it throws a Tcase code and will not allow any commands on the dash switches to be allowed to perform any kind of Tcase range selection. Its just lost.

The TCCM is like thc PCM except the TCCM controls the Tcase and the PCM controls the engine and tranny.

 

[Fless]

See other thread

Transfer case won't shift

worked fine, Quit working and was stuck in 2x4. then got ***** and was stuck in automatic 4x4, Then back in 2x4 and so on. ended in 4x4 automatic. Changed out swithc, Module, motor, and finally the solenoid to the diff, One at a time. Early on when replaced the control module I tried battery...

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