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DTC P0508: IAC Valve Sense Circuit Low: Testing

  1. Start the engine. Allow the engine to idle. If the engine will not idle, maintain an engine speed between 800-1500 RPM. With the DRBIII® scan tool, read the IAC current. Is the IAC current below 146 milliamps? If yes, go to next step. If no, see INTERMITTENT CONDITION  under SELF-DIAGNOSTIC SYSTEM.
  2. Turn the ignition off. Disconnect the IAC motor harness connector. Remove the IAC motor. Inspect the IAC air passages for restriction and damage to the IAC valve. Measure the resistance across the IAC motor pin terminals (component). Is the resistance within 8.7-10.7 ohms? If yes, go to next step. If no, replace the IAC motor.
    3. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool (8815) to perform diagnosis.
  3. Turn the ignition off. Disconnect the IAC motor harness connector. Disconnect the PCM harness connectors. Measure the resistance of the (K60) IAC signal circuit from the IAC motor harness connector to the appropriate terminal of Miller Special Tool (8815). Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the (K60) IAC signal circuit.
  4. Turn the ignition off. Disconnect the IAC motor harness connector. Disconnect the PCM harness connectors. Measure the resistance between ground and the (K60) IAC signal in the IAC motor harness connector. Is the resistance below 100 ohms? If yes, repair the short to ground in the (K60) IAC signal circuit. If no, go to next step.
  5. Turn the ignition off. Disconnect the IAC motor harness connector. Disconnect the PCM harness connectors. Measure the resistance between ground and the (K39) IAC motor control circuit in the IAC motor harness connector. Is the resistance below 100 ohms? If yes, repair the short to ground in the (K39) IAC motor control circuit. If no, go to next step.
    6. CAUTION: Do not probe the PCM harness connectors. Probing the PCM harness connectors will damage the PCM terminals resulting in poor terminal to pin connection. Install Miller Special Tool (8815) to perform diagnosis.
  6. Turn the ignition off. Disconnect the IAC motor harness connector. Disconnect the PCM harness connectors. Measure the resistance of the (K39) IAC return circuit from the IAC motor harness connector to the appropriate terminal of Miller Special Tool (8815). Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the (K39) IAC motor control circuit.
  7. Before continuing disconnect the PCM harness connector and check the related wiring terminals for corrosion, damage or terminal push out. Repair as necessary. Pay particular attention to all power and ground circuits. If there are no possible causes remaining, replace and program the PCM. See PROGRAMMING .
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