2006 Silverado will only run in Auto 4WD!

Jarmon · July 1, 2019

2006 Silverado - 150,000mi

Recently, while driving at hwy speed my 4wd randomly tried to shift into 4-low, this was accompanied by the "service 4wd" message on the dash. It disengaged like it was in neutral (I could press the gas and RPM's went up but nothing else) and as soon as I was almost stopped on the side of the road it finally engaged and slammed into 4-low. I then shifted to neutral and hit the 2wd button then reverse and then drive and it went back into 2wd, started driving and it happened again twice. So the fourth time I went to Auto 4wd instead of 2wd and it got me back home (Of course i was 2 hrs away from home when this happened). I have replaced the button switch and cleaned the ground wires but that's it, no change. My next thought is the TCCM because it seems like the TCEM is functioning but just receiving the wrong signals? Could the front diff actuator cause issues back in the Transfer Case? Has anyone heard of anything like this or can help point me in the right direction? I know its probably not good to keep driving on pavement in Auto 4wd...

davester · July 1, 2019

I would suggest getting codes read from the computer. Basic ODBII code readers won't read it, a parts store might, a regular mechanics shop should be able to, and the dealer will be able to.

I would probably first look for a problem with wiring, maybe rubbed through somewhere between the switch and the computer.

Edited July 1, 2019 by davester

Jarmon · July 1, 2019

1 hour ago, davester said:

I would suggest getting codes read from the computer. Basic ODBII code readers won't read it, a parts store might, a regular mechanics shop should be able to, and the dealer will be able to.

I would probably first look for a problem with wiring, maybe rubbed through somewhere between the switch and the computer.

Mechanic came back with a C0327 code "encoder circuit".

DeePa · July 1, 2019

Probably the encoder motor on the transfer case.

Theres also a ground on the drivers side frame you should check out too.

Edited July 1, 2019 by DeePa

Jarmon · July 1, 2019

10 minutes ago, DeePa said:

Probably the encoder motor on the transfer case.

Theres also a ground on the drivers side frame you should check out too.

I checked the ground wires on the frame. But yeah looking like I'm going to change the encoder motor tomorrow. I'll update with the results.