Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the IAC valve.
- Ignition ON, probe all of the IAC harness connector terminals with a test lamp connected to B+. The test lamp should illuminate on one pair of the following terminals:
- Terminals A and D
- Terminals B and C
- If the test lamp illuminates on a circuit other than a circuit in the pair, test the isolated circuit for a short to ground. If the circuit tests normal, replace the ECM.
- If the test lamp does not illuminate on both circuits in the pair, test the applicable control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
- Probe all of the IAC harness connector terminals with a test lamp connected to ground. The test lamp should illuminate on one pair of the following terminals:
- Terminals A and D
- Terminals B and C
- If the test lamp does not illuminate on both circuits in the pair, test the applicable control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the ECM.
- Ignition OFF for 20 seconds. Ignition ON, repeat steps 2 and 3 in order to verify all circuits test normal.
- If all circuits test normal, inspect for the following:
- A clogged IAC passage
- Excessive deposits on the throttle plate or bore
- Excessive deposits on IAC valve pintle or bore
- Restricted air intake system
- The throttle body for damage and/or tampering
- Vacuum leaks
- Malfunctioning PCV valve
- If all conditions test normal, test or replace the IAC valve.
IMPORTANT:
The ECM controls the IAC control circuits in pairs. One pair will be grounded, while the other pair is supplied a voltage.