I have a 2002 Avalanche and my service 4wd light comes on randomly. I will get in to leave work at night and the light is on and when I get up the next morning to go to work it is out. It will be off for a few days and then it will light up again and then go away again 1-4 starts later I am assuming I have a sensor problem or a wire problem. When I check the codes in memory I get CO308 Mortor AB circuit low and CO315 Motor ground circuit open. Anyone got any suggestions or had a similar problem that can shed some light on this??

 

The poster j cAT in the AutomotiveForums thread 2000 Silverado C0315 Service 4wheel drive - Automotive Forums .com Car Chat knows what he's talking about. The encoder motor is bi-directional and thus there is no dedicated ground circuit to/from the motor. The open ground circuit is actually between the transfer case shift control module over the BLK wire at connector C2, terminal C and grounding point G110.