Pinpoint Test B: DTC P0645

WARNING: This page is about a different car, the 2014 Ford F-150. 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 CBB77 (WH).
  
  Fig 1: Measuring Voltage Between A/C Clutch Relay Socket And Ground
  Courtesy of FORD MOTOR CO.
Is the voltage greater than 11 volts?
- Yes : GO to B2 .
- No : VERIFY BJB fuse 77 (10A) is OK. If OK, REPAIR circuit CBB77 (WH) for an open. TEST the system for normal operation. If not OK, REFER to the OEM WIRING DIAGRAMS to identify the possible causes of the circuit short.
B2 CHECK THE A/C CLUTCH RELAY
- Carry out the A/C clutch relay component test.
  Refer to OEM WIRING DIAGRAMS COMPONENT TESTING for component testing.
Did the relay pass the component test?
- Yes : GO to B3 .
- No : INSTALL a new A/C clutch relay. TEST the system for normal operation.
B3 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: PCM C1381B (5.0L, 6.2L).
- Disconnect: PCM C175B (3.7L).
- Disconnect: PCM C1551B (3.5L).
- Ignition ON.
- For 3.7L, 5.0L and 6.2L
  
  Fig 2: Measuring Voltage Between Ground And PCM C1381B-18, Circuit CH302
  Courtesy of FORD MOTOR CO.
  
  Measure the voltage between ground and:
  - For 3.7L, PCM C175B-12 , circuit CH302 (WH/BN), harness side.
  - For 5.0L and 6.2L, PCM C1381B-12 , circuit CH302 (WH/BN), harness side.
- For 3.5L
  
  Fig 3: Measuring Voltage Between Ground And PCM C1551B-2, Circuit CH302
  Courtesy of FORD MOTOR CO.
  
  For 3.5L, measure the voltage between ground and PCM C1551B-2 , circuit CH302 (WH/BN), harness side.
Is any voltage present?
- Yes : REPAIR the circuit.
- No : GO to B4 .
B4 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
- For 3.7L, 5.0L and 6.2L
  
  Fig 4: Measuring Resistance Between Ground And PCM C1381B-12, Circuit CH302
  Courtesy of FORD MOTOR CO.
  
  Measure the resistance between ground and:
  - For 3.7L, PCM C175B-12 , circuit CH302 (WH/BN), harness side.
  - For 5.0L and 6.2L, PCM C1381B-12 , circuit CH302 (WH/BN), harness side.
- For 3.5L
  
  Fig 5: Measuring Resistance Between Ground And PCM C1551B-2, Circuit CH302
  Courtesy of FORD MOTOR CO.
  
  For 3.5L, measure the resistance between ground and PCM C1551B-2 , circuit CH302 (WH/BN), harness side.
Is the resistance greater than 10, 000 ohms?
- Yes : GO to B5 .
- No : REPAIR the circuit.
B5 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR AN OPEN
- For 3.7L, 5.0L and 6.2L
  
  Fig 6: Checking A/C Clutch Relay Coil Switched Ground Circuit For Open
  Courtesy of FORD MOTOR CO.
  
  Measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and:
  - For 3.7L, PCM C175B-12 , circuit CH302 (WH/BN), harness side.
  - For 5.0L and 6.2L, PCM C1381B-12 , circuit CH302 (WH/BN), harness side.
- For 3.5L
  
  Fig 7: Measuring Resistance Between A/C Clutch Relay Socket, Circuit CH302 And PCM C1551B-2
  Courtesy of FORD MOTOR CO.
  
  For 3.5L, measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C1551B-2 , circuit CH302 (WH/BN), harness side.
Is the resistance less than 3 ohms?
- Yes : GO to B6 .
- No : REPAIR the circuit.
B6 CHECK FOR CORRECT PCM OPERATION
- Ignition OFF.
- Disconnect and inspect all PCM connectors.
- Repair:
  - corrosion (install new connector or terminals - clean module pins)
  - damaged or bent pins - install new terminals/pins
  - pushed-out pins - install new pins as necessary
- Connect all PCM connectors. Make sure they seat and latch correctly.
- Operate the system and determine if the concern is still present.
Is the concern still present?
- Yes : CHECK OASIS for any applicable TSBs . If a TSB exists for this concern, DISCONTINUE this test and FOLLOW TSB instructions. If no TSB addresses this concern, INSTALL a new PCM. REFER to POWERTRAIN CONTROL MODULE (PCM) .
- No : The system is operating correctly at this time. The concern may have been caused by a loose or corroded connector. ADDRESS the root cause of any connector or pin issues.