Pinpoint Test A: DTC P0645
Climate Control System
Pinpoint Tests
Pinpoint Test A: DTC P0645
Refer to Wiring Diagrams for schematic and connector information. Diagrams By Number
Normal Operation
Under normal operation, voltage is provided to the A/C clutch relay coil. 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) - The DTC sets when the PCM grounds the relay circuit, excessive current draw is detected on the relay circuit or, with the relay circuit not grounded by the PCM, voltage is not detected on the relay circuit the PCM expects to detect voltage coming through the relay coil to the relay circuit.
This pinpoint test is intended to diagnose the following:
- Wiring, terminals or connectors
- A/C clutch relay
- PCM
PINPOINT TEST A: DTC P0645
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A1 CHECK THE VOLTAGE TO THE A/C CLUTCH RELAY
- Ignition OFF.
- Disconnect: A/C Clutch Relay.
- Ignition ON.
- Measure the voltage between A/C clutch relay socket, circuit CBB77 (WH) and ground.
- Is the voltage greater than 10 volts?
Yes
CARRY OUT the A/C clutch relay component test.
Refer to Compressor Clutch Relay for component testing.
If the relay tests OK, GO to A2.
No
REPAIR circuit CBB77 (WH) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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A2 CHECK A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO VOLTAGE
- Ignition OFF.
- Disconnect: For 4.6L and 5.4L engines, PCM C175B.
- Disconnect: For 6.8L engines, PCM C1551E.
- Ignition ON.
For 4.6L and 5.4L engines
- For 4.6L and 5.4L engines: Measure the voltage between ground and PCM C175B-2, circuit CH302 (WH/BN).
For 6.8L engines
- For 6.8L engines: Measure the voltage between ground and PCM C1551E-3, circuit CH302 (WH/BN).
- 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 A3.
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A3 CHECK A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND
- Ignition OFF.
For 4.6L and 5.4L engines
- For 4.6L and 5.4L engines: Measure the resistance between ground and PCM C175B-2, circuit CH302 (WH/BN).
For 6.8L engines
- For 6.8L engines: Measure the resistance between ground and PCM C1551E-3, circuit CH302 (WH/BN).
- Is the resistance greater than 10,000 ohms?
Yes
GO to A4.
No
REPAIR circuit CH302 (WH/BN) for a short to ground. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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A4 CHECK A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR AN OPEN
For 4.6L and 5.4L engines
- For 4.6L and 5.4L engines: Measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C175B-2, circuit CH302 (WH/BN), harness side.
For 6.8L engines
- For 6.8L engines: Measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C1551E-3, circuit CH302 (WH/BN).
- Is the resistance less than 5 ohms?
Yes
GO to A5.
No
REPAIR circuit CH302 (WH/BN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.
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A5 CHECK THE PCM CONNECTION
- Disconnect all the PCM connectors.
- Inspect the HVAC 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.
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