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HVAC - Automatic




DTC P0645, P0646, or P0647

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

* Review Strategy Based Diagnosis Strategy Based Diagnosis for an overview of the diagnostic approach.

* Diagnostic Procedure Instructions Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptor

DTC P0645
- Air Conditioning A/C Clutch Relay Control Circuit

DTC P0646
- Air Conditioning A/C Clutch Relay Control Circuit Low Voltage

DTC P0647
- Air Conditioning A/C Clutch Relay Control Circuit High Voltage

Diagnostic Fault Information






Circuit System Description

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the A/C clutch relay control circuit. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volt. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage.

Conditions for Running the DTC

* The ignition voltage is between 11-18 volts.

* The engine speed is greater than 600 RPM.

* An A/C request is made.

Conditions for Setting the DTCs

The ECM detects an open, short to ground, or short to voltage on the control circuit of the A/C compressor clutch relay when commanded OFF with the engine in crank or run status.

Action Taken When the DTC Sets

The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.

Conditions for Clearing the DTC

A history DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction.

Reference Information

Schematic Reference

HVAC Schematics HVAC - Automatic

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (M30)

Description and Operation

* Air Delivery Description and Operation Air Delivery

* Air Temperature Description and Operation Air Temperature

Electrical Information Reference

* Circuit Testing Circuit Testing

* Connector Repairs Connector Repairs

* Testing for Intermittent Conditions and Poor Connections Testing for Intermittent Conditions and Poor Connections

* Wiring Repairs Wiring Repairs

Scan Tool Reference

Control Module References Control Module References for scan tool information

Circuit/System Verification

Ignition ON, command the A/C Relay ON and OFF with a scan tool. Feel/listen for the A/C relay to click.

Circuit/System Testing

1. Ignition OFF, disconnect the A/C compressor relay.

2. Ignition ON.

3. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground.

• If the test lamp does not illuminate
Repair the open/high resistance in the circuit.

• If the test lamp illuminates

4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.

• If the test lamp does not illuminate
Replace the underhood fuse block.

• If the test lamp illuminates

5. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.

6. Verify the test lamp turns ON and OFF when commanding the A/C relay ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the X1 harness connector at the engine control module, ignition ON.

2. Test for less than 1 V between the control circuit and ground.

• If 1 V or greater, repair the short to voltage on the circuit.

• If less than 1 V

3. Ignition OFF.

4. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, replace the engine control module.

• If the test lamp is always ON

5. Ignition OFF, disconnect the X1 harness connector at the engine control module.

6. Test for infinite resistance between the control circuit and ground.

• If less than infinite resistance, repair the short to ground on the circuit.

• If infinite resistance, replace the engine control module.

• If the test lamp turns ON and OFF

7. Verify that a test lamp does not illuminate between the control circuit terminal 87 and ground.

• If the test lamp illuminates
Repair the short to voltage on the circuit.

• If the test lamp does not illuminate

8. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the A/C compressor clutch. It may take up to 2 minutes for all vehicle systems to power down.

9. Test for less than 5 ohms between the ground circuit terminal A and ground.

• If 5 ohms or greater

1. Ignition OFF.

2. Test for less than 2 ohms in the ground circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the ground circuit.

• If less than 2 ohms, repair the open/high resistance in the ground connection.

• If less than 5 ohms

10. Connect the harness connector at the A/C compressor clutch.

11. Ignition ON, connect a 10 A fused jumper wire between the B+ circuit terminal 30 and control circuit terminal 87.

12. Verify the A/C compressor clutch is activated.

• If the A/C compressor clutch does not activate

1. Ignition OFF.

2. Test for less than 2 ohms in the control circuit end to end.

• If 2 ohms or greater, repair the open/high resistance in the circuit.

• If less than 2 ohms, test or replace the A/C compressor clutch.

• If the A/C compressor clutch activates

13. Test or replace the A/C compressor relay.

Component Testing

1. Ignition OFF, disconnect the A/C compressor relay.

2. Test for 60-180 ohms between terminals 85 and 86.

• If less than 60 ohms or greater than 180 ohms
Replace the A/C compressor relay.

• If between 60-180 ohms

3. Test for infinite resistance between the terminals listed below:

* 30 and 86

* 30 and 87

* 30 and 85

* 85 and 87

• If less than infinite resistance
Replace the A/C compressor relay.

• If infinite resistance

4. Install a 30 A fused jumper wire between relay terminal 86 and 12 V. Install a jumper wire between relay terminal 85 and ground. Test for less than 2 ohms between terminals 30 and 87.

5. Test for less than 2 ohms between terminals 30 and 87.

• If 2 ohms or greater
Replace the A/C compressor relay.

• If less than 2 ohms

6. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Control Module References Control Module References for ECM replacement, setup, and programming

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