C0306, C0321, C0327 Explained And Common Failures

[carnau]

Hey Everyone. Thought I would explain a little about the transfer case codes we run into on these vehicles and how to diagnose and repair it if you run into it.

 

!!!ALWAYS CHECK YOUR POWERS AND GROUNDS FROM THE START!!!

Power Comes from the under hood fuse block. TREC Fuse 30Amp. It is HOT at all times.

Ground is G110 Located on the Frame, Body mount under driver’s door.

 

C0306 Motor A or B Circuit

On the C0306, One thing to check for is that the grounds tend to cause this concern. I have run into many loose or broken grounds from other components using the main ground for the encoder motor and interfering with it. So check all your grounds. Battery ground to the engine and frame, the Head ground most likely will cause this. G110 is the Encoder motor main ground. It’s located on the frame rail under the driver’s door attached to the body mount bracket.

 

C0321 Transfer Case Lock Circuit

On the C0321, Check the Transfer case control module for corrosion in the connector. If you ever had a windshield replaced and it wasn’t sealed right. It seems to be the place the water wants to go. Check for water intrusion on the connector. Another common failure is when encoder has been replaced or repaired and the position sensor was not aligned correctly. I will be making a video of how to install a new sensor and the alignment process for this as well. Again, Check ground G110 just to be on the safe side. I like to remove and clean this ground whenever I do this job.

 

C0327 Encoder Circuit Malfunction

On the C0327, Check to see if the wiring harness is in the bracket. Sometimes the wiring harness will not be installed correctly after a repair was done (replacing transmission, transfer case, encoder, and it will hang down and rub the front drive shaft. This will cause a number of issues, many of times I have seen this. If all the wiring tests good, more than likely you have an encoder motor position sensor failure. Replace the sensor and the gasket and it should repair the concern. Again, Check G110 just to be on the safe side.

 

 

 

 

 

Edited June 29, 2020 by carnau

[KHE]

I have a 2013 Silverado that had the SERVICE 4WD SYSTEM MESSAGE when I start the truck.  I have the C0306  code.  I've verified a good ground at G110 (the frame by the body mount but you mention a bad head ground will cause this code.  Where is the 'head ground" on a '13 Silverado?

 

Thank you.