GM Rear Differential Clutch Control Module

GM Rear Differential Clutch Control Module Post-Repair Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired GM Rear Differential Clutch Control Module and the problem is still happening.
Important: Please do not open/disassemble the module. Opening the module can damage it and may void warranty coverage.

Common symptoms this guide helps with:

• All-Wheel Drive (AWD) warning light stays on and won’t clear
• No communication with the module
• AWD feels inoperative or inconsistent

Step 1: Confirm the exact symptom

• Is the AWD warning light ON all the time, or only sometimes?
• Does the scan tool communicate with the Rear Differential Clutch Control Module?
• Did the issue begin after battery work, collision work, water intrusion, or rear differential service?

Step 2: Battery / voltage check

• Low voltage can cause module resets and communication faults.
• Confirm the vehicle starts normally and the charging system is stable before deeper diagnosis.

Step 3: Check AWD / Rear Diff / DRIVELINE fuses first

• Use the fuse box legend and check all fuses related to:
  • AWD / Rear Differential / Driveline / RDM / FDCM (wording varies)
  • IGN feeds and battery feeds
• If any fuse is blown, stop and inspect wiring to the rear differential and harness routing for shorts.

Step 4: Do a clean key-cycle reset

• Key OFF, wait 60 seconds.
• Key ON (engine can stay off) for 10 seconds.
• Start the vehicle and see if the AWD light behavior changes.

Step 5: Inspect the module connector and harness at the rear differential
This is the #1 cause of “AWD light stays on” and “no communication.”

• Key OFF.
• Unplug and reseat the connector until the lock fully clicks.
• Inspect for:
  • Corrosion/green tint on pins
  • Moisture/water marks
  • Bent or pushed-back pins
  • Damaged wiring near the connector (chafing, tight bends, rubbed-through insulation)

Step 6: Check for water intrusion and physical damage

• These modules are exposed to road splash.
• If you see water/corrosion in the connector area, the vehicle-side connector/harness must be repaired or the issue can return even with a good module.

Step 7: Scan the vehicle and record codes (critical step)
Perform a full vehicle scan and save:

• Codes from the Rear Differential/AWD module (if it communicates)
• ABS codes (wheel speed sensor faults can disable AWD)
• BCM/PCM codes related to network/voltage
  If your scan tool can’t see the module at all, keep going—Steps 8–10 focus on “no communication.”

Step 8: Clear codes and re-test

• Clear all codes.
• Drive the vehicle briefly (or do a short loop in a parking lot).
• Re-scan and note which codes return immediately.

Step 9: If the module communicates but AWD light stays on
This often points to a vehicle-side input/output issue:

• Wheel speed sensor / ABS fault disabling AWD
• Rear differential clutch/actuator issue
• Harness damage causing intermittent signal loss
• Low voltage or ground drop under load
  Focus on the codes that return first—those usually point to the root cause.

Step 10: If there is NO communication with the module
No-comm is most commonly caused by power/ground or wiring, not the module itself.

• Re-check Step 3 (fuses) and Step 5 (connector/pins)
• Inspect the harness from the rear differential forward for pinch points or rubbed-through spots
• If the issue is intermittent (works sometimes), suspect corrosion or a broken wire inside the insulation near the connector

Step 11: If the problem is intermittent
Try to identify the trigger:

• After rain/wash → connector moisture/corrosion likely
• Only cold mornings → weak connection, marginal power/ground, or harness strain
• After bumps → harness break or loose connector lock
  Recheck connector seating and harness routing with this in mind.

Step 12: What to send UpFix if issues continue

• VIN
• Exact symptom (AWD light on / no-comm / both)
• Full code list (module + code numbers)
• Whether the module communicates on your scan tool
• Clear photos of the connector/pins and any corrosion or wiring damage
• When it happens (constant vs intermittent, rain/cold/bumpy roads)