Pinpoint Test B: DTC P0645, P0646 or P0647

Climate Control System

Pinpoint Test B: DTC P0645, P0646 or P0647

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)- This DTC 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.

- DTC P0646 (A/C Clutch Relay Control Circuit Low)- (Diesel only) This DTC sets when the relay circuit is off and ground 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.

- DTC P0647 (A/C Clutch Relay Control Circuit High)- (Diesel only) This DTC sets when the PCM grounds the relay circuit and excessive current draw (short to voltage) is detected on the relay circuit.

This pinpoint test is intended to diagnose the following:

- Wiring, terminals or connectors

- A/C clutch relay

- PCM

PINPOINT TEST B : DTC P0645, P0646 OR P0647

B1 CHECK THE A/C CLUTCH RELAY

- Ignition OFF.

- Carry out the A/C clutch relay component test.

Does the relay test OK?

Yes

For DTC P0645, GO to B2.

For DTC P0646, GO to B4.

For DTC P0647, GO to B5.

No
INSTALL a new A/C clutch relay. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

B2 CHECK THE VOLTAGE TO THE A/C CLUTCH RELAY

- Disconnect: A/C Clutch Relay.

- Ignition ON.

- Measure the voltage between ground and the A/C clutch relay socket, circuit CBB35 (YE/GY).





Is the voltage greater than 10 volts?

Yes
GO to B3.

No
VERIFY Battery Junction Box (BJB) fuse 35 (10A) is OK. If OK, REPAIR circuit CBB35 (YE/GY) for an open. CLEAR the DTCs. REPEAT the self-test. 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

B3 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR AN OPEN

- Ignition OFF.

- Disconnect: PCM C175B (Gasoline).

- Disconnect: PCM C1232B (Diesel).

- For gasoline engines





Measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C175B-12, circuit CH302 (WH/BN), harness side.

- For diesel engines





Measure the resistance between A/C clutch relay socket, circuit CH302 (WH/BN) and PCM C1232B-2, circuit CH302 (WH/BN), harness side.

Is the resistance less than 5 ohms?

Yes

For gasoline engines, GO to B4.

For diesel engines, GO to B6.

No
REPAIR circuit CH302 (WH/BN) for an open. CLEAR the DTCs. REPEAT the self-test. TEST the system for normal operation.

B4 CHECK THE A/C CLUTCH RELAY COIL SWITCHED GROUND CIRCUIT FOR A SHORT TO GROUND

- Disconnect: PCM C175B (Gasoline).

- Disconnect: PCM C1232B (Diesel).

- For gasoline engines





Measure the resistance between ground and PCM C175B-12, circuit CH302 (WH/BN), harness side.

- For diesel engines





Measure the resistance between ground and PCM C1232B-2, circuit CH302 (WH/BN), harness side.

Is the resistance greater than 10,000 ohms?

Yes

For gasoline engines, GO to B5.

For diesel engines, GO to B6.

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 A SHORT TO VOLTAGE

- Disconnect: PCM C175B (Gasoline).

- Disconnect: PCM C1232B (Diesel).

- Ignition ON.

- For gasoline engines





Measure the voltage between ground and PCM C175B-12, circuit CH302 (WH/BN), harness side.

- For diesel engines





Measure the voltage between ground and PCM C1232B-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 B6.

B6 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.