Chevrolet Trax: DTC P0645, P0646, OR P0647: Air conditioning (A/C) compressor clutch relay

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

Diagnostic Instructions

• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.
• Review Strategy Based Diagnosis for an overview of the diagnostic approach.
• Diagnostic Procedure Instructions provides an overview of each diagnostic category.

DTC Descriptors

DTC P0645

Air Conditioning (A/C) Compressor Clutch Relay Control Circuit

DTC P0646

Air Conditioning (A/C) Compressor Clutch Relay Control Circuit Low Voltage

DTC P0646

Air Conditioning (A/C) Compressor Clutch Relay Control Circuit Low Voltage

DTC P0647

Air Conditioning (A/C) Compressor Clutch Relay Control Circuit High Voltage

Diagnostic Fault Information

Circuit/System Description

When the A/C switch is pressed, the HVAC control module sends a serial data message to the engine control module (ECM) indicating the A/C request. In response to this message, the ECM grounds the A/C compressor clutch relay control circuit energizing the A/C compressor clutch relay. With the relay contacts closed, battery voltage is applied through the A/C compressor clutch control circuit activating the A/C compressor clutch

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 DTC

P0645 or P0646

The ECM detects a short to ground or an open at the A/C compressor clutch relay control circuit.

P0647

The ECM detects a short to voltage at the A/C compressor clutch relay control circuit.

Action Taken When the DTC Sets

P0645 or P0646

The A/C compressor is inoperative or always active

P0647

The A/C compressor is inoperative.

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 (Encore)

Connector End View Reference

WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - ENCORE WIRING SYSTEMS AND POWER MANAGEMENT - COMPONENT CONNECTOR END VIEWS - INDEX - TRAX

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference

• Circuit Testing
• Connector Repairs
• Testing for Intermittent Conditions and Poor Connections
• Wiring Repairs

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions (LUV) , Powertrain Diagnostic Trouble Code (DTC) Type Definitions (2H0)

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF, and all vehicle systems OFF. Disconnect the harness connector at the Q2 A/C Compressor Clutch. It may take up to 2 min for all vehicle systems to power down.
2. Test for less than 10 ohms between the Q2 A/C Compressor Clutch ground circuit terminal A and ground.

If 10 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 circuit.
• If less than 2 ohms, repair the open/high resistance in the ground connection.

If less than 10 ohms

3. Connect a test lamp between the control circuit terminal B and ground, ignition ON.
4. Verify the test lamp does not turn ON and OFF when commanding the Q2 A/C Compressor Clutch On and Off with a scan tool.

If the test lamp turns ON and OFF

Test or replace the Q2 A/C Compressor Clutch

If the test lamp does not turn ON and OFF

5. Ignition OFF, connect the harness connector at the Q2 A/C Compressor Clutch. Disconnect the X3 harness connector at the X50A Fuse Block - Underhood, ignition ON.
6. Verify the Q2 A/C Compressor Clutch is not activated.

If the Q2 A/C Compressor Clutch is activated

1. Ignition OFF, disconnect the harness connector at the Q2 A/C Compressor Clutch, ignition ON.
2. Test for less than 1 V between the control circuit terminal B and ground.

• If 1 V or greater, repair the short to voltage on the circuit.
• If less than 1 V, test or replace the Q2 A/C Compressor Clutch.

If the Q2 A/C Compressor Clutch is not activated

7. Connect a 10 A fused jumper wire between the control circuit terminal B5 and B+.
8. Verify the Q2 A/C Compressor Clutch activates.

If the Q2 A/C Compressor Clutch does not activate

1. Ignition OFF, remove the jumper wire, disconnect the harness connector at the Q2 A/C Compressor Clutch, ignition ON.
2. 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

3. 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 Q2 A/C Compressor Clutch.

If the Q2 A/C Compressor Clutch activates

9. Ignition OFF, connect the X3 harness connector at the X50A Fuse Block - Underhood and disconnect the harness connector at the K20 Engine Control Module, ignition ON.
10. Verify the Q2 A/C Compressor Clutch is not activated.

If the Q2 A/C Compressor Clutch is activated

1. Ignition OFF, disconnect the X3 harness connector at the X50A Fuse Block - Underhood.
2. Test for infinite resistance between the X3 X50A Fuse Block - Underhood control circuit terminal B4 and ground.

• If less than Infinite resistance, repair the short to ground on the circuit.
• If infinite resistance, test or replace the X50A Fuse Block - Underhood.

If the Q2 A/C Compressor Clutch is not activated

11. Connect a 3 A fused jumper wire between the K20 Engine Control Module control circuit terminal for the KR29 A/C Compressor Clutch Relay and ground.
12. Verify the Q2 A/C Compressor Clutch activates.

If the Q2 A/C Compressor Clutch does not activate

1. Ignition OFF, remove the jumper wire, disconnect the X3 harness connector at the X50A Fuse Block - Underhood, ignition ON.
2. Test for less than 1 V between the X3 X50A Fuse Block - Underhood control circuit terminal B4 and ground.

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

3. 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 X50A Fuse Block - Underhood.

If the Q2 A/C Compressor Clutch activates

13. Replace the K20 Engine Control Module.

Component Testing

Compressor Clutch Test

1. Ignition OFF, disconnect the Q2 A/C Compressor Clutch.
2. Test for 3.9 - 4.3 ohms between terminals A and B

If not between 3.9 - 4.3 ohms

Replace the Q2 A/C Compressor Clutch.

If between 3.9 - 4.3 ohms

3. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• HVAC Component Replacement Reference
• Front Compartment Fuse Block Replacement
• Control Module References for engine control module replacement, programming and setup

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