Audi A3 ECU/ECM

Audi A3 ECU/ECM Post-Repair Troubleshooting Guide (2003–2008)

Important: Use this guide if you reinstalled your repaired Audi A3 ECU/ECM and the problem is still happening.
Important: Please do not open/disassemble the ECU. Opening it can damage the unit and may void warranty coverage.

This guide helps with:

• No communication (DTC 01314 / ECM no communication)
• Check Engine Light / MIL return
• Engine power loss
• Intermittent communication faults

Step 1: Confirm correct ECU and connectors are fully seated

• Verify the ECU part number matches the original unit removed from the vehicle
• Make sure the ECU plugs are fully seated and the locking levers are fully latched
• Inspect connector pins for bent pins, corrosion, moisture, or pushed-out terminals

Step 2: Battery voltage and power stability

• Confirm battery is fully charged and terminals are tight/clean
• Low voltage during cranking can cause false communication faults and drivability issues
• Inspect main grounds (battery-to-body and engine-to-chassis) for looseness/corrosion

Step 3: Check ECU power supply fuses and ECU power relay(s)

• Check all engine management/ECU fuses using a test light or meter (don’t rely on visual only)
• Verify the ECU power relay(s) clicks/operates normally
• If a fuse blows again, stop and locate the short before continuing

Step 4: If the complaint is “01314 / ECM no communication”

• Confirm your scan tool can communicate with other modules (ABS, cluster, etc.)
• If only the ECU won’t communicate:
  • Re-check ECU power and grounds
  • Inspect ECU relay/fuse feeds again
  • Inspect the harness near the ECU box/plenum area for water intrusion or damage
• If multiple modules won’t communicate:
  • Focus on vehicle power/ground issues or CAN network wiring faults first

Step 5: Power loss / reduced power after reinstall

• Scan for codes and record which ones return first after clearing
• Verify these common vehicle-side causes:
  • Boost/charge leaks (loose clamps, cracked hoses, disconnected pipes)
  • MAF/MAP sensor connection issues
  • Vacuum line issues to control valves/actuators (if equipped)
  • Throttle body connector seated and secure
• If power loss started right after other work (battery, wiring, sensor replacement), re-check what was touched first

Step 6: Clear codes and perform a controlled re-test

• Clear all ECU/engine faults
• Start the engine and let it idle until warm (if possible)
• Perform a short test drive
• Re-scan immediately and note the first returning codes (those are the most important)

Step 7: Quick harness/connector sanity checks (no disassembly)

• Wiggle-check the harness near ECU and main engine harness junctions while idling (if safe)
• Inspect for rubbed-through wiring, oil-soaked connectors, or stretched wiring near recent repairs
• Verify coil/injector/engine sensor connectors are fully locked

What to send us if the problem continues

• VIN
• ECU part number from the label
• Exact symptom (no comm, power loss, CEL, etc.)
• All codes that return after clearing (especially the first ones)
• Any recent repairs (battery work, wiring/sensor replacement, water intrusion, jump starts)