STUCK in 4LO! Code P2771

CapnDean · October 28, 2020

2009 Silverado 3500HD DRW Gas: Code P2771, Service 4wd Light illuminated. Shifter knob buttons illuminate at engine start but immediately extinguish.

Here's what happened; I used 4Hi to get out of a sticky spot - I did my usual coasting in neutral return to 2wd shift. When I got on hard pavement and took off....it was evident I was still in 4Hi.

I pull off to the side of the road and started screwing with the knob trying to get it to shift OUT of 4Hi when it shifted into 4L and hasn't budged since.

I read the code: 4WD Low Switch Circuit. (Okay Duh...its stuck in 4LO so yes its gotta be that!). No amount of monkeying with the transmission (shifting fwd to reverse & neutral) while working the transfer case shifter knob has any impact.

I cleaned the grounds at the frame, they are all bright and make a solid ground. No Joy.

The 30 AMP fuse in position 67 (TREC) has not blown. Is there another fuse that operates the transfer case? I cannot find it if there is.

I replaced the shift motor with a brand new AC delco unit. No Joy.

It is important to know that the transfer case position indicator light does NOT light up (indicating that the TC is in 4LO) - I know that the light in the switch is good because it comes on when I start the truck, BUT: Normally there is a tell tale amber light showing that you're in 2HI or 4HI or whatever. Another symptom of this is that my speedometer is reading ZERO when moving in 4LO.

I also disconnected the battery for 30 minutes etc... trying to re-boot the computer hoping that might do it. No luck.

While changing the shift motor I did check to see if I could manually move the shaft that the shift motor turns and it does not appear to be jammed in any way. IF I KNEW WHICH WAY to turn it, I would at least manually shift it out of 4LO so that I could at least drive it!

PLEASE somebody who has experienced this before help out and tell me what's next!