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DTC P0645: A/C Clutch Relay Circuit: Testing

  1. Turn ignition on, engine not running. With the DRBIII®, actuate the A/C Clutch Relay. Is the A/C Clutch Relay operating? Relay is located in Power Distribution Center (PDC). If yes, go to next step. If no, go to step  3.
    2. 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.
  2. The conditions that set the DTC are not present at this time. The following may help in identifying the intermittent condition. With the engine running at normal operating temperature, monitor the DRBIII® 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® Freeze Frame information. If possible, try to duplicate the conditions under which the DTC was set. With the DRBIII®, actuate the A/C Clutch Relay. Wiggle the wire harness from the A/C Clutch Relay to the PCM while the relay is actuating. Refer to any Technical Service Bulletins (TSB) that may apply. Visually inspect the related wire harness. Look for any chafed, pierced, pinched, or partially broken wires. Visually inspect the related wire 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.
  3. Turn the ignition off. Remove the A/C Clutch Relay from the PDC. Turn ignition on, engine not running. Measure the voltage on the Fused Ignition Switch Output circuit at the A/C Clutch Relay harness connector in the PDC. Is the voltage above 11.0 volts? If yes, go to next step. If no, repair the open/short to ground in the Fused Ignition Switch Output circuit. Check and replace any open fuses.
  4. Turn ignition off. Measure the resistance of the A/C Clutch Relay between the Fused Ignition Switch Output terminal and the A/C Clutch Relay Control terminal (component side). Is the resistance between 60 and 80 ohms? If yes, go to next step. If no, replace the A/C Clutch Relay.
    5. 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. Use Miller Special Tool (8815) when performing diagnosis at PCM harness connectors.
  5. Ensure the ignition is off. Disconnect the PCM harness connectors. Measure the resistance of the A/C Clutch Relay Control circuit from the A/C Clutch Relay harness connector in the PDC to the appropriate terminal of the Miller Special Tool. Is the resistance below 5.0 ohms? If yes, go to next step. If no, repair the open in the A/C Clutch Relay Control circuit.
  6. Measure the resistance between ground and the A/C Clutch Relay Control circuit in the A/C Clutch Relay harness connector in the PDC. Is the resistance below 5.0 ohms? If yes, repair the short to ground in the A/C Clutch Relay Control circuit. If no, go to next step.
    7. NOTE: Before continuing, check the PCM harness connectors for corrosion, damage or terminal push out. Repair as necessary.
  7. There are no possible causes remaining, replace PCM. Program the new PCM. See PROGRAMMING .
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