Drivetrain codes galore! 2003 Sierra 1500HD 6.0L

[DangerDan]

I engaged 4WD for the first time on my truck over the weekend (the truck is new to me). It seemed to work fine and saved me from a second attempt at a hill, and shifted back into 2WD without issue when I was done with the slope. On my way home from this trip, my dash popped up with the message "Service 4WD." Just for shits and giggles, I tried 4WD again in my driveway, and everything but 4-lo works (I did not try 4-Lo), but the message popped up again.

 

I took the truck to a local shop and had them pull codes, and... WOW.

 

C0300 - rear prop shaft speed sensor

C0305 - fwd prop shaft speed sensor

C0306 - transfer case motor?

C0321 - TCase lock circuit malfunction

C0327 - TCase Encoder Circuit Malfunction

C0359 - 4WD Low Range

C0374  - TCase system malfunction

C0379 - Front Axle Malfunction

 

He said there were a ton more but the shop was swamped and didn't have time to write all of them down. He basically said it threw every power train code in the book. Has anybody seen this sort of thing before? I strongly doubt that I have this many legitimate problems with my 4WD system given that it seemed to work just fine...

 

The closest thing to a malfunction that I've seen is that when I left the shop after having codes pulled, my 4WD switch panel had the N light illuminated red as I drove through the parking lot. I pulled into a spot, pressed the 2WD button, and that light illuminated immediately (it did not appear to ever have actually been in N-- wheelpower was present and normal-- only the light), and I drove home without issue.

 

To be fully honest, I've got no idea where to start on this and I'm looking for suggestions. Any help is appreciated.

 

[SierraHD17]

Clear them all.. most are probably the result of one.  The usual in those trucks is the CO327 which is the sensor ring in the encoder motor.  What you describe is the result of the sensor ring losing its marbles and throwing the service 4wd message.  Yes the grounds on the drivers cab mount could be bad or the dash switch but 9 times out of 10 it's the encoder sensor ring with issues. 

[DangerDan]

Thanks man, I should have one coming on Friday. If it makes the error go away, yay, if not it is only a $50 part. I appreciate the quick reply.