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Idle Air Control Valve Control Signal Check

  1. Disconnect harness connector for IAC valve. See Figure. Connect (US 1115) LED tester (using adapter cable from connector test kit VW 1594) between terminal No. 1 of harness connector and engine ground. See Figure.
  2. Crank starter for a few seconds. LED tester must light up. If NO: Verify that injector valve circuit breaker S72 and EVAP frequency valve circuit breaker S75 in electronic control box are Okay.
  3. Check continuity between terminal No. 1 of IAC valve harness connector and EVAP frequency valve circuit breaker S75, using wiring diagram. Resistance must be 0.5 ohm maximum. See WIRING DIAGRAMS .
  4. Check continuity between EVAP frequency valve circuit breaker S75 and terminal No. 31 of fuel pump relay -J17- (relay location 6). See Figure.
  5. Check control signal to fuel pump relay. See FUEL PUMP RELAY CONTROL SIGNAL .
    6. NOTE: Positive voltage supply must always be present at terminal No. 1, regardless of which Output DTM is called up.
  6. Reconnect LED tester. Activate Output DTM. See OUTPUT DIAGNOSTIC TEST MODE (DTM) in SELF-DIAGNOSTICS article. LED tester must light up. If LED tester does NOT light up: Connect (VAG 1598) test box (using VAG 1598/5 adapter cable), to Engine Control Module (ECM) harness connector. See CONNECTING (VAG 1598) TEST BOX . ECM remains disconnected.
  7. Check continuity (according to wiring diagram) between terminal No. 1 of IAC valve harness connector, see Figure and terminal No. 37 of test box. See Figure. See WIRING DIAGRAMS .
  8. If NO continuity: Repair open circuit between terminal No. 37 of ECM harness connector and terminal No. 1 of IAC valve harness connector. See WIRING DIAGRAMS .
  9. If NO open circuit: Replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article. LED tester must blink when IAC valve is activated (blinking may be weak but must occur).
  10. Remove test box and (VAG 1598/5) adapter cable. Reconnect ECM.
  11. Connect LED tester (using adapter cable) to terminal No. 1 and 2 of IAC valve harness connector.
  12. Activate Output DTM. See OUTPUT DIAGNOSTIC TEST MODE (DTM) in SELF-DIAGNOSTICS article.
  13. LED tester must blink when IAC valve is activated (blinking may be weak but must occur).
  14. If LED tester does NOT blink, or if it lights up continuously, connect (VAG 1598) test box (using VAG 1598/5 adapter cable), to ECM harness connector. See CONNECTING VAG 1598 TEST BOX .
  15. ECM remains disconnected If LED tester is continuously lit, check for continuity between terminal No. 2 of IAC valve harness connector and terminal No. 4 of test box. ECM remains disconnected.
  16. If LED tester is continuously lit, check for continuity between terminal No. 2 of IAC valve harness connector and terminal No. 4 of test box.
  17. If LED tester does NOT blink, check for continuity between terminal No. 2 of IAC valve harness connector and terminal No. 4 of test box.
  18. If NO continuity: Repair short to ground or open circuit between terminal No. 2 of IAC valve harness connector and terminal No. 4 of ECM harness connector. See Figure.
  19. If NO open circuit or short to ground, replace ECM. After replacement of ECM, see ECM IDENTIFICATION and ECM CODING under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS article.
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