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Mil Check: A4

  1. Turn ignition on. MIL should light. If MIL lights, go to step 5). If MIL does not light, go to next step.
  2. MIL is not lighting due to faulty wiring or an open circuit. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. PCM is located in left rear corner of engine compartment inside electrical box. Connect VAG 1598/22 test box to PCM wiring harness. See Figure .
  3. Connect a jumper wire between test box sockets No. 2 and 17. Turn ignition on. MIL should light. If MIL does not light, go to next step.
  4. Turn ignition off. Inspect MIL bulb. If bulb is okay, check for an open circuit between MIL and PCM. See WIRING DIAGRAMS article. If wiring is okay, replace faulty PCM. See PCM REPLACING  .
  5. Start engine and let it idle. MIL should go out after a few seconds. If MIL goes out, MIL is functioning properly. If MIL does not go out, check for any stored DTCs. See RETRIEVING CODES  under SELF-DIAGNOSTIC SYSTEM. If DTCs are stored, repair as necessary. If no DTCs are stored, go to next step.
  6. MIL is on continuously due to a short to ground. Turn ignition off. Disconnect Powertrain Control Module (PCM) connectors. Connect VAG 1598/22 test box to PCM wiring harness. See Figure .
  7. Connect a DVOM between test box socket No. 17 and ground. DVOM should indicate infinity (no resistance). If DVOM reading is not as specified, go to next step. If DVOM reading is as specified, go to step 9).
  8. Check for a short circuit between MIL and Powertrain Control Module (PCM). See WIRING DIAGRAMS article.
  9. If no continuity is present and there is no short to ground, replace faulty PCM. See PCM REPLACING  .
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