4X4 Service Light with No light on switch - 2006 4.2L EXT

[Royalwapiti]

I am starting a thread, I was posting in another but I hi-jacked that thread so this one is my own. I am starting from scratch. Transfer Case fluid has never been changed - 74,000 miles, including two 4000 mile round trips to AZ from Iowa in August and November. Didn't use 4x4on any of them.

4x4 didn't want to leave 4HI then when it did the trouble light came on and led on switch went out. Stuck in 2HI

- Replaced TCCM with salvage yard model from same year - 2006 no change $65

- Replaced switch with brand new napa model. No change $25

- Checked voltages on connector at Encoder Motor, was getting 5v reference and 12-14v at other terminal and small numbers on the data pins.

- Replaced Encoder Motor with salvage yard model (2008 - NP8) $0 (traded back the TCCM) Service light went off 2 HI light was on, until I tried putting into 4HI then 4HI and 2HI stayed lit until I shut vehicle off. When i restarted it the service 4x4 light was on and the switch lights were off.

- Took to my local mechanic, he Tech II it and got a C0327 code, Encoder Circuit said there was history codes of C0306 , C0321 and C0327. He swore every time he gets a code C0327 he changes the Encoder and that fixes it. I gave him my history (after he diagnosed it) he said to try another encoder, salvage yard must be bad. FYI I saw a mouse in the hood insulation, thinking it could be a chewed wire.

- Today salvage yard exchanged the encoder motor and I put it on. Service light went off, 2 HI was on, until I tried putting into 4HI then 4HI and 2HI stayed lit until I shut vehicle off. When i restarted it the service 4x4 light was on and the switch lights were off.

Back to where I was.

Any suggestions on what to try next?


Does the wiring and controls for the encoder go through the Actuator? Could that be bad and causing the system to shutdown? A guy has one available locally for $20 might try that before getting a salvage yard transfer case.

If I climb under and try turning the gear shaft on the transfer case where the encoder goes, could I or should i be able to turn it by hand (with vise-grips on) assuming engine is running. Transfer cases are available locally for $175 to $250. Much rather do that than screw with the stealership. But if it is a chewed wire I might need them to track it down.

Thanks

 

[mrphoenix80]

STOP THROWING PARTS and diag it. Most likely its a broken wire. For the 1Hour of diag at the dealer or good independant that knows this system it will cost less than you have already spent. You have replaced the whole system for an electrical concern that a $.50 butt connector could fix.

A mouse you say, under the hood?????? Thats a good starting point right there. I could start a 50 page thread on what mice do in vehicles, from odd smells to wiring nightmares.

Now on to the tech advise... Test the gray wire for 5v ref @4.5v-5.2 only, more or less is a problem. Test the blk/wht wire for ground at the encoder motor. Test the brn/wht wire from the encoder to the TCCM for continuity. Also check your module grounds @ g102(near the underhood fusebox) and g105 (on cowl near I/P harness pass through) and make sure they are good. That is the overview of the diag tree. The replacement parts listed are parts you have replaced already. The transfer case is NOT in the list of parts to replace for this code.

Oh BTW all these circuits run through C101 a 38pin connector to the right of the right of the underhood fuse block. This should help you narrow down where the fault is in the harness.

 

[The_Roadie]

Does the wiring and controls for the encoder go through the Actuator?

No. I've posted the schematics.

And it should be very clear that a 2HI->A4WD transition sends commands to BOTH the actuator and the encoder motor. The A4WD->4HI transition only involves the encoder motor. You can often troubleshoot the system by listening to the noises, but when you have evidence of data communication failures from the PCM to the TCCM, all rationality is gone. Deeper troubleshooting of the data comm system is called for.

In general: failures downstream from the TCCM cause blinking lights on the mode control switch.

Transfer case control shafts can be turned by hand.

 

[Royalwapiti]

Thanks for the answers guys.

I think, based on Roadie's response about blinking indicator lights I will have the dealer troubleshoot....looking the ECM-TCCM area.

Snowstorm coming Thursday may need to shift into 4HI manually....that'll bring back memories of having to get out and lock in the hubs of the old days.

 

[BRomanJr]

Thanks for the answers guys.

I think, based on Roadie's response about blinking indicator lights I will have the dealer troubleshoot....looking the ECM-TCCM area.

Snowstorm coming Thursday may need to shift into 4HI manually....that'll bring back memories of having to get out and lock in the hubs of the old days.

On the NP8 (auto4wd) Transfercase you cannot shift to 4wd manually and have it stay, the encoder turns the shaft to engage a clutch pack and holds the position with an encoder brake.
Don't forget to change the Transfer Fluid while you have it up in the air. (was due at 50k, clutch pack will thank you)

 

[Royalwapiti]

On the NP8 (auto4wd) Transfercase you cannot shift to 4wd manually and have it stay, the encoder turns the shaft to engage a clutch pack and holds the position with an encoder brake.
Don't forget to change the Transfer Fluid while you have it up in the air. (was due at 50k, clutch pack will thank you)

Thanks, have appt for Wednesday to troubleshoot and will see what the dealership charges to change that.

 

[Royalwapiti]

STOP THROWING PARTS and diag it. Most likely its a broken wire. You have replaced the whole system for an electrical concern that a $.50 butt connector could fix.

HARUMPF

Spent $204 at dealer to tell me something inside the transfer case is binding on the encoder motor. Need new transfer case, $2000 approximately plus installation.

I guess my parts throwing was taking me in the right direction. I now have plans for the weekend...

Thinking out loud if I should mess with trying some new fluid before swapping the TC.

 

[The_Roadie]

... new transfer case, $2000 approximately plus installation....

At only $1500 LIST PRICE for a new TC from GM, less from parts4chevys.com, they're still screwing ya.

Ebay.

car-parts.com

Anybody but those folks asking $2000.

 

[Royalwapiti]

Just following up.

I put the replacement TCase in today. Had to wait for the electrical connector I pulled the wires out of. I bought extras...

I put in a TCase from an 03 ($200). Fit right in and appears to work while on the jackstands. Even hear the usual clunk when it goes out of 4Lo.

Thanks for the help guys.