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DTC P0508: IAC Motor Sense Circuit Low: Testing

NOTE: If the engine will not idle, maintain an engine speed 800-1500 RPM.
  1. Start the engine. Allow the engine to idle. With the DRBIII(R), read the IAC current. Is the IAC current less than 146 milliamps? If yes, go to next step. If no, go to step  8 .
    2. NOTE: Inspect the IAC motor air passages for restriction and damage to the IAC motor.
  2. Turn the ignition off. Disconnect the IAC motor harness connector. Remove the IAC motor. Measure the resistance across the IAC motor terminals (component side). Is the resistance 8.7-10.7 ohms? If yes, go to next step. If no, replace IAC motor.
  3. Disconnect the PCM harness connectors. Measure the resistance of the IAC motor sense circuit between the IAC motor harness connector and the PCM harness connector. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair IAC sense circuit for an open.
  4. Measure the resistance between ground and the IAC motor sense circuit in the IAC motor harness connector. Is the resistance less than 5.0 ohms? If yes, repair the IAC motor sense circuit for a short to ground. If no, go to next step.
  5. Measure the resistance between ground and the IAC motor driver circuit in the IAC motor harness connector. Is the resistance less than 5.0 ohms? If yes, repair the IAC motor driver circuit for a short to ground. If no, go to next step.
  6. Measure the resistance of the IAC motor driver circuit between the IAC motor harness connector and the PCM harness connector. Is the resistance less than 5.0 ohms? If yes, go to next step. If no, repair the IAC motor driver circuit for an open.
  7. There are no possible causes remaining, replace PCM.
    8. WARNING: When the engine is operating, DO NOT stand in a direct line with the fan. DO NOT put your hands near the pulleys, belts or fan. DO NOT wear loose clothing.
  8. Conditions that set DTC are not present at this time. The following list may help in identifying the intermittent condition:
    • With the engine running at normal operating temperature, monitor the DRBIII(R) parameters related to the DTC while wiggling the wiring harness. Look for parameter values to change and/or a DTC to set.
    • Review the DRBIII(R) Freeze Frame information to identify under what conditions the DTC set.
    • Refer to any Technical Service Bulletin (TSB) that may apply.
    • Visually inspect the related wiring harness. Look for any chafed, pierced, pinched, or partially broken wires.
    • Visually inspect the related wiring harness connectors. Look for broken, bent, pushed out, or corroded terminals.

      Were any of the above conditions present? If yes, repair as necessary. If no, test is complete.

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