Any ideas: C0321 - Transfer case lock circuit


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Hey all, I have a '05 4.2 AWD EXT with the dreaded SERVICE 4WD LIGHT lit on the cluster. My brother-in-law has access to a TECH2, and was able to read the code, confirm the selector switch was functioning, but nothing else. Neither of us are proficient with the tool.... Anyhow, in the past I have had several AWD harness issues which caused me to re-run several wires down the harness which solved the other issues. This time I checked continuity of each circuit from the encoder to the connector under the hood, and all 7 were good. It could be the encoder motor, but I'd rather not just replace parts and hope. So 2 questions:
  1. Can the encoder motor be bench tested?
  2. What else could a C0321 be?
Any thoughts would be appreciated.


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Thread Starter
Ok - just answered my first question by reading the post just before mine.... I can do the bench test now.


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Thread Starter
Solved - it turned out to be the transfer case encoder motor. I bench tested as outlined by The Roadie in:

and found the motor brake to be intermittent. I found a used motor @ Tiger for $75, cleaned the connections, and am now back pulling heavy stuff up hills in soft soil.

One note here to those who follow - the biggest challenge with the bench test was connecting the leads to the pins in the connector. What I did, which worked quite well, was to snip a std terminal in half, which allowed it to securely and compactly fit over the pin in the connector. Sorry - I could not figure out how to paste a pic....

Thanks Roadie. :wooot:

Chris JW

Registered Member
In testing mine i went to hardware store and the had narrow female"spade" connectors which also worked out well


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Resurrecting this Old Question of "What could this C0321 Code Be...?" with a pair of Pro Diagnosis YT Videos as an FYI addition using the On Screen Visual Diagnostic Procedures and Solutions courtesy some High End Scanning Equipment that most of us do not have:

Best Practices here?

(1) Reading and Understanding the GM-GMC 4WD System Circuits.
(2) Checking Powers & Grounds on LOADED Circuits with Basic Tools.
(3) Getting Dirty enough to locate WHERE the Hidden Broken Wire(s) are.
(4) Having 'Nice Equipment' is NICE... But NOT Essential.
(5) Using Good, Common Sense in Wire Tracing & Choice Test Locations.
(6) Use a PICO 2204A or Hantek 1008C OS to Diagnose the Class 2 U10000 Code.


BBBINDUSTRIES No Longer Offers FREE On-Line TSBs and Wiring Diagrams.

Part 1:


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