Volvo Differential Electronic Module

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

Important: Use this guide if you reinstalled your repaired Volvo 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:

• All-Wheel Drive (AWD) not working
• “Complete high-speed network failure” / multiple communication faults
• DEM not communicating on a scan tool

Step 1: Confirm the exact symptom

• Is AWD inoperative only, or do you have multiple warnings across the vehicle?
• Can your scan tool communicate with the DEM at all?
• Did the problem start after battery replacement, alternator work, jump-starting, or water intrusion?

Step 2: Check battery voltage and charging health first
Low voltage can cause network faults and make modules appear “dead.”

• Confirm the vehicle starts normally.
• If you have frequent low battery messages, address that before chasing AWD faults.

Step 3: Check fuses related to AWD/DEM (and ignition feeds)
Using your fuse box legend, check all fuses that reference:

• AWD / DEM / AOC / Rear differential
• ECU/TCM/ABS power feeds (network stability depends on these too)
  If any fuse is blown, stop and inspect the harness for shorts before replacing it again.

Step 4: Perform a clean power reset

• Key OFF, remove key, wait 2 minutes.
• Start vehicle and see if DEM communication changes.
  If the issue is intermittent, note whether it returns after driving or after a restart.

Step 5: Inspect the DEM connector and pins (very important)
This is the most common vehicle-side cause of DEM faults.

• Key OFF.
• Unplug and reseat the DEM connector until the lock fully clicks.
• Inspect for:
  • Corrosion/green residue on pins
  • Moisture/water marks
  • Bent or pushed-back pins
  • Damaged wiring near the connector (chafed, pinched, stretched)

Step 6: Inspect for water intrusion at the rear differential area
DEM location is exposed to road splash on many Volvo AWD platforms.

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

Step 7: Run a full vehicle scan and save the results
A “complete high-speed network failure” message often involves more than one module.

• Record codes from:
  • DEM (if it communicates)
  • ABS/Brake module (wheel speed sensor faults can disable AWD)
  • ECM/TCM/BCM (network/voltage codes)
    If multiple modules show “no communication,” go to Step 8.

Step 8: If multiple modules show “no communication”
This usually points to a network/power issue rather than the DEM alone.

• Re-check battery/charging stability
• Re-check main power and ground connections (especially underhood and chassis grounds)
• Look for recent work areas (battery tray, underhood fuse box, repairs near harness routing)

Step 9: If DEM does NOT communicate but other modules do
Focus on DEM power/ground and its local harness:

• Re-check AWD/DEM fuses again
• Inspect DEM harness routing from the rear differential forward for:
  • Rubbed-through insulation
  • Pinched sections near brackets/clips
  • Previous repairs/splices

Step 10: If DEM communicates but AWD still doesn’t work
AWD disable can be commanded by other systems.

• Pay close attention to ABS / wheel speed sensor codes
• If ABS is unhappy, AWD may be shut down as a safety strategy
• Clear codes, drive briefly, and see which codes return first

Step 11: If the issue is intermittent
Track the trigger:

• After rain/wash → connector moisture/corrosion likely
• After bumps → harness break/loose connector lock likely
• Only on cold starts → marginal connection or power/ground issue likely

Step 12: What to send UpFix if problems continue

• VIN
• Exact symptom (AWD not working / DEM no-comm / network failure)
• Full code list + which modules will/won’t communicate
• Whether issue is constant or intermittent (and what triggers it)
• Clear photos of the DEM connector/pins and any corrosion or harness damage