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Pinpoint Test B: DTC P0645

  1. B1 CHECK THE VOLTAGE TO THE A/C CLUTCH RELAY 
    • Ignition OFF.
    • Disconnect: A/C Clutch Relay.
    • Ignition ON.
    • Measure the voltage between ground and the A/C clutch relay socket, circuit CBB46 (WH/BU).
      Fig 1: Measuring Voltage Between Ground And A/C Clutch Relay Socket, Circuit CBB46 (WH/BU)
      G06064519Courtesy of FORD MOTOR CO.
    • Is the voltage greater than 10 volts? 
    • Yes  : CARRY OUT the A/C clutch relay component test.

      Refer to the appropriate procedure in COMPONENT TESTING for component testing.

      If the relay tests OK, GO to B2.

    • No  : REPAIR circuit CBB46 (WH/BU) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  2. B2 CHECK CIRCUIT CH302 (WH/BN) FOR A SHORT TO VOLTAGE 
    • Ignition OFF.
    • Disconnect: PCM C175b.
    • Ignition ON.
    • Measure the voltage between ground and PCM C175b-18, circuit CH302 (WH/BN), harness side.
      Fig 2: Measuring Voltage Between Ground And PCM C175B-18, Circuit CH302 (WH/BN), Harness Side
      G06064520Courtesy of FORD MOTOR CO.
    • Is any voltage present? 
    • Yes  : REPAIR circuit CH302 (WH/BN) for a short to voltage. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
    • No  : GO to B3.
  3. B3 CHECK CIRCUIT CH302 (WH/BN) FOR A SHORT TO GROUND 
    • Ignition OFF.
    • Measure the resistance between ground and PCM C175b-18, circuit CH302 (WH/BN), harness side.
      Fig 3: Measuring Resistance Between Ground And PCM C175B-18, Circuit CH302 (WH/BN), Harness Side
      G06064521Courtesy of FORD MOTOR CO.
    • Is the resistance greater than 10,000 ohms? 
    • Yes  : GO to B4.
    • No  : REPAIR circuit CH302 (WH/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  4. B4 CHECK CIRCUIT CH302 (WH/BN) FOR AN OPEN 
    • Measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C175b-18, circuit CH302 (WH/BN), harness side.
      Fig 4: Measuring Resistance Between A/C Clutch Relay Socket And PCM C175B-18, Circuit CH302 (WH/BN), Harness Side
      G06064522Courtesy of FORD MOTOR CO.
    • Is the resistance less than 5 ohms? 
    • Yes  : GO to B5.
    • No  : REPAIR circuit 321 (GY/WH) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
  5. B5 CHECK THE PCM MODULE CONNECTION 
    • Clear the DTCs.
    • Disconnect all the PCM connectors.
    • Check for:
      • corrosion.
      • pushed-out pins.
      • incorrectly seated connector.
    • Connect and correctly seat all the PCM connectors.
    • Operate the system.
    • Does the concern return? 
    • Yes  : INSTALL a new PCM. TEST the system for normal operation.
    • No  : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector.
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