NEED HELP Service 4x4 light and strange symptoms

captain150

Original poster
Member
Jan 27, 2018
9
Edmonton, AB
Hi I took a look thru the 4x4 troubleshooting thread, seems for people with similar symptoms the issue was the TCCM. My truck is a 2006.

I made a video see below.

www.youtube.com/watch?v=Y-Wl_7f8d2s

Basically it doesn't seem like the truck even tries to switch out of auto mode, unless I move the knob with the ignition off, then it will blink. I don't think I hear either the encoder motor or the front actuator.
I tried exercising the switch a whole bunch. No change.

If the problem was the actuator or encoder motor, the light should blink on a new setting right? It also takes some time for the service 4x4 light to come on when the ignition is turned on.
 

Reprise

Lifetime VIP Donor
Supporting Donor
Member
Jul 22, 2015
2,724
Something you can try before going farther...

(with key off) remove the mode knob, check for any corrosion on the pins, etc. - then reseat it and test. Sometimes the switch gets flaky - it has happened to others, including me. Normally, you'll see the mode indicator light flashing, though, as you mentioned.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
I think it could be either the switch or the encoder motor. In my experience, if it was the TCCM, the lights on the switch just go out or not light at all. In fact, looking at the video, I think it's the encoder motor. When you turn the the switch to 2hi before turning on the ignition, the switch does register it and flashes then gives up, stays on AWD and turns on the service 4x4 light. And I don't hear anything from the encoder motor.

But that is all guess work. Best would be to get a scanner scanner and pull the error code from the TCCM. Someone with a Tech 2 would be the best but a Blluetooth OBD adapter with the Car Gauge Pro Android app might work.
 

captain150

Original poster
Member
Jan 27, 2018
9
Edmonton, AB
Thanks for the help. I did just get a bluetooth OBD2 scanner and used dashcommand with GM enhancements to get the following codes;

P0300 - random misfire
P0418 - secondary air pump
C0035 - left front wheel speed sensor
C0455 - steering angle sensor
C0244 - PWM delivered torque
U1026 - lost comm with TCCM


U1026 is the only one that seemed to be related. After clearing the codes a couple days ago, it hasn't come back. The previous owner mentioned he had a mechanic diagnose the system and they probably tried the pulling fuses method to reset the TCCM. I should have mentioned he said the mechanic also figured it was the encoder motor. What threw me for a loop is I don't hear the front actuator either.

C0244 and C0455 came back after the stabilitrak engaged on some ice, but the service stabilitrak light isn't on (it was on for that trip, but turned off after cycling the ignition). Probably a flaky angle sensor, don't think it's related to the 4x4 issue.

Could my scanner be missing some additional codes from the TCCM?

I'm thinking of just trying a junkyard encoder motor and seeing what happens.
 

Mooseman

Moderator
Dec 4, 2011
25,257
Ottawa, ON
The lost communication was probably an old code. With most of these codes, you have to scan it when the light is on, otherwise, it clears itself.

You could certainly try a used encoder. My money is still on that.
 

captain150

Original poster
Member
Jan 27, 2018
9
Edmonton, AB
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