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DTC P0508: IAC Motor Sense Circuit Low: Testing

  1. Start engine and let it idle. If engine will not idle, hold engine speed between 800 and 1500 RPM. Using scan tool, read IAC CURRENT. If IAC CURRENT is less than 146 milliamps, go to next step. If IAC CURRENT is 146 milliamps or more, go to step  8 .
  2. Turn ignition off. Disconnect IAC motor harness connector located on top of throttle body. Remove IAC motor. Inspect IAC air passages for restriction. Also, inspect IAC valve for damage. Repair as necessary. If no problems are found, measure resistance between IAC motor terminals. If resistance is 8.7-10.7 ohms, go to next step. If resistance is not 8.7-10.7 ohms, replace IAC motor.
  3. Disconnect PCM harness connectors. PCM is located in engine compartment, between air cleaner and radiator. Measure resistance of sense circuit (Brown/White wire) between IAC motor harness connector and terminal No. 57 at PCM C2 harness connector. See Figure . If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in sense circuit.
  4. Measure resistance between ground and sense circuit (Brown/White wire) at IAC motor harness connector. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground in sense circuit.
  5. Measure resistance between ground and driver circuit (Yellow/Black wire) at IAC motor harness connector. If resistance is 5 ohms or more, go to next step. If resistance is less than 5 ohms, repair short to ground in driver circuit.
  6. Measure resistance of driver circuit (Yellow/Black wire) between IAC motor harness connector and terminal No.49 at PCM C2 harness connector. If resistance is less than 5 ohms, go to next step. If resistance is 5 ohms or more, repair open in driver circuit.
  7. If no other possible causes are remaining, replace PCM.
  8. Conditions that set DTC are not present at this time. Perform the following to help identify intermittent condition:
    • With engine running at normal operating temperature, wiggle related wiring harness while monitoring related parameters on scan tool. If voltage changes or DTC sets while wiggling wiring harness, repair connectors or wiring harness where wiggling caused voltage to change or DTC to set.
    • Review freeze frame information on scan tool. Duplicate conditions present when DTC was set.
    • Refer to any Technical Service Bulletins (TSBs) that may apply.
    • Visually inspect related wiring harness. Check for chafed, pierced, pinched or partially broken wires.
    • Visually inspect related wiring harness connectors. Check for broken, bent, pushed out or corroded terminals.

    If a problem is found, repair as necessary. If no problems are found, test is complete.

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