Volvo Gen. 5 Differential Electronic Module

Volvo Gen. 5 Differential Electronic Module (DEM) Post-Repair Troubleshooting Guide

Important: Use this guide if you reinstalled your repaired Volvo Gen. 5 Differential Electronic Module (DEM) 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:

• AOC pump not working
• Communication issues with the DEM
• High-speed network issues caused by the DEM
• Traction control warning message(s)

Step 1: Confirm the symptom type

• Is the main issue AOC pump not working, DEM no-communication, or traction/ABS warnings?
• Is the problem constant, or intermittent (only after rain, bumps, cold start, etc.)?

Step 2: Check battery voltage and charging health first
Low voltage can trigger traction warnings and CAN/network faults.

• If the vehicle has weak-start symptoms, battery/charging messages, or recent jump-starts, address that first.

Step 3: Perform a full scan and note what modules communicate

• Can your scan tool communicate with ABS, ECM, and BCM normally?
• Does the DEM communicate?
• Save the code list before clearing anything.

Step 4: Quick power reset

• Key OFF, remove key, wait 2 minutes.
• Start vehicle and re-scan.
  If the DEM shows up only sometimes, treat it as a connection/power/ground issue first.

Step 5: Inspect the DEM connector and pins (most important step)

• Key OFF.
• Unplug the DEM connector and reseat it until the lock fully clicks.
• Inspect for:
  • Corrosion/green residue on pins
  • Moisture/water marks
  • Bent, spread, or pushed-back pins
  • Damaged wiring within a few inches of the connector (chafing/pinch)

Step 6: Check for water intrusion at the module location
Gen. 5 DEMs are often exposed to road spray.

• If there is moisture/corrosion at the connector, the connector/harness must be repaired or the issue can return.

Step 7: Check AWD/DEM/AOC-related fuses (and ignition feeds)
Use the vehicle’s fuse legend and check any fuse labeled:

• AWD / DEM / AOC / Rear differential / Pump
  If any fuse is blown, do not replace it repeatedly—inspect harness and pump circuit for a short.

Step 8: If the DEM does NOT communicate, but other modules do
Focus on DEM power/ground and the local harness:

• Re-check the DEM/AWD fuses
• Inspect harness routing from the rear differential area forward for rub-through or pinched sections
• Look for recent work areas (rear suspension work, exhaust work, battery work)

Step 9: If the DEM communicates, but you get traction control warnings
Traction warnings can be caused by other systems that disable AWD.

• Pay close attention to ABS / wheel speed sensor codes
• Clear codes, drive briefly, and see what returns first
  If ABS codes return first, fix those first—AWD/traction can be disabled as a safety strategy.

Step 10: If the AOC pump is “not working”
This can be pump, wiring, power/ground, or DEM control-related.

• Check for AWD/DEM/AOC pump related codes
• If you have no AOC/DEM codes but AWD is still inoperative, treat it as a vehicle-side pump/wiring issue first
• If the issue is intermittent (works then stops), suspect connector/harness moisture or an intermittently failing pump circuit

Step 11: If the issue happens after rain, car wash, or wet roads
That strongly points to:

• Moisture intrusion at the DEM connector
• Corrosion in pins
• Water wicking into the harness
  Dry/clean/repair the connector/harness before suspecting the module again.

Step 12: What to send UpFix if problems continue

• VIN
• Exact symptom (AOC pump not working / DEM no-comm / traction warning / network faults)
• Full code list + which modules will/won’t communicate
• Whether issue is constant or intermittent (and what triggers it)
• Clear photos of DEM connector pins and any corrosion/water intrusion