P0645
Climate Control System
Pinpoint Test B: DTC P0645
Normal Operation
Voltage is provided to the A/C clutch relay coil from Battery Junction Box (BJB) fuse 77 (10A). When A/C is requested and A/C line pressures allow, a ground is provided to the A/C clutch relay coil from the PCM, energizing the A/C clutch relay.
- DTC P0645 (A/C Clutch Relay Control Circuit)- sets when the PCM grounds the relay circuit and more voltage than expected is detected on the relay circuit. The DTC also sets when the relay circuit is off and no voltage is detected on the relay circuit. The PCM expects to detect voltage coming through the relay coil to the relay circuit when it is not grounding it.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- A/C clutch relay
- PCM
PINPOINT TEST B : DTC P0645
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).
Is the voltage greater than 10 volts?
Yes
GO to B2.
No
VERIFY BJB (Battery Junction Box) 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 Wiring Diagrams to identify the possible causes of the circuit short [1][2]Diagrams By Number.
B2 CHECK THE A/C CLUTCH RELAY
- Carry out the A/C clutch relay component test.
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
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
For 3.5L, measure the voltage between ground and PCM C1551B-2, circuit CH302 (WH/BN), harness side.
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 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
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
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 circuit CH302 (WH/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
B5 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR AN OPEN
- For 3.7L, 5.0L and 6.2L
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
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 5 ohms?
Yes
GO to B6.
No
REPAIR circuit 302 (WH/BN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
B6 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the PCM connectors for:
- corrosion
- pushed-out terminals
- damaged terminals
- Connect and correctly seat all the PCM connectors.
- Clear the DTCs.
- Enter the following diagnostic mode on the scan tool: Self-Test- PCM.
- 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.