Pinpoint Test B: DTC P0645

WARNING: This page is about a different car, the 2010 Mercury Milan, 2010 Lincoln MKZ, and 2010 Ford Fusion. However, it is still accessible from the selected car via links, so may be relevant.

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 CBK03 (GY).
  
  Fig 1: Measuring Voltage Between Ground & A/C Clutch Relay Socket, Circuit CBK03 (GY)
  Courtesy of FORD MOTOR CO.
- Is the voltage greater than 10 volts?
- Yes: CARRY OUT the A/C clutch relay component test.
  Refer to COMPONENT TESTING -- GASOLINE MODELS .
  
  If the relay tests OK, GO to B2.
- No: REPAIR circuit CBK03 (GY) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
B2 CHECK CIRCUIT CH302 (WH/BN) FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: PCM C175B.
- Ignition ON.
- For 2.5L and 3.0L only , measure the voltage between ground and PCM C175B-12, circuit CH302 (WH/BN), harness side.
  
  Fig 2: Measuring Voltage Between Ground & PCM C175B-12, Circuit CH302 (WH/BN), Harness Side
  Courtesy of FORD MOTOR CO.
- For 3.5L only , measure the voltage between ground and PCM C175B-64, circuit CH302 (WH/BN), harness side.
  
  Fig 3: Measuring Voltage Between Ground & PCM C175B-64, Circuit CH302 (WH/BN), Harness Side
  Courtesy 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.
B3 CHECK CIRCUIT CH302 (WH/BN) FOR A SHORT TO GROUND
- Ignition OFF.
- For 2.5L and 3.0L only , measure the resistance between ground and PCM C175B-12, circuit CH302 (WH/BN), harness side.
  
  Fig 4: Measuring Resistance Between Ground & PCM C175B-12, Circuit CH302 (WH/BN), Harness Side
  Courtesy of FORD MOTOR CO.
- For 3.5L only , measure the resistance between ground and PCM C175B-64, circuit CH302 (WH/BN), harness side.
  
  Fig 5: Measuring Resistance Between Ground & PCM C175B-64, Circuit CH302 (WH/BN), Harness Side
  Courtesy 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.
B4 CHECK CIRCUIT CH302 (WH/BN) FOR AN OPEN
- For 2.5L and 3.0L only , measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C175B-12, circuit CH302 (WH/BN), harness side.
  
  Fig 6: Checking Circuit CH302 (WH/BN) For Open (For 2.5L & 3.0L Only)
  Courtesy of FORD MOTOR CO.
- For 3.5L only , measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C175B-64, circuit CH302 (WH/BN), harness side.
  
  Fig 7: Checking Circuit CH302 (WH/BN) For Open (For 3.5L Only)
  Courtesy of FORD MOTOR CO.
- Is the resistance less than 5 ohms?
- Yes: GO to B5.
- No: REPAIR circuit CH302 (WH/BN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
B5 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the module connectors for:
  - corrosion.
  - pushed-out terminals.
  - damaged terminals.
- Connect and correctly seat all the PCM connectors.
- Clear the DTCs.
- Operate the system and verify the concern is still present.
- Is the concern still present?
- 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.