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.

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 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), HVAC Schematics (Trax)

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

Manual 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 terminal A and terminal B.

If not between 3.9 - 4.3 ohms

Replace the Q2 A/C Compressor Clutch.

If between 3.9 - 4.3 ohms

3. Test for infinite resistance between terminal A and ground.

If less than infinite resistance

Replace the Q2 A/C Compressor Clutch.

If infinite resistance

4. All OK.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the repair.

• HVAC Component Replacement Reference (C67), HVAC Component Replacement Reference (C60), HVAC Component Replacement Reference (C41)
• Front Compartment Fuse Block Replacement
• Control Module References for engine control module replacement, programming and setup

Symptoms - HVAC Systems - manual

NOTE: The following steps must be completed before using the symptom tables:

1. Perform the Diagnostic System Check - Vehicle before using the HVAC System Malfunction procedure in order to verify that all of the following are true:

• There are no DTCs set.
• The control modules can communicate via the serial data link.

2. Review the system operation in order to familiarize yourself with the system functions. Refer to Manual HVAC Description and Operation.

Visual/Physical Inspection

• Inspect for aftermarket devices which may affect the operation of the HVAC System. Refer to Checking Aftermarket Accessories .
• Inspect the easily accessible or visible system components for obvious damage or conditions which may cause the symptom.
• Verify the A/C compressor turns freely and is not seized.
• Verify that the customer is using the correct key to enable personalization and is not inadvertently activating auxiliary HVAC controls.
• The A/C compressor will not operate in cold outside air temperatures.
• The following conditions may cause window fogging:

• Wet carpet or mats
• High humidity
• Interior water leak
• Blocked A/C evaporator drain tube
• Maximum passenger capacity
• Blocked body pressure relief valves

• Inspect the air distribution system for causes of reduced air flow:

• Obstructed or dirty passenger compartment air filter, if equipped
• Blocked or damaged air inlet or outlet vents

Intermittent

Faulty electrical connections or wiring may be the cause of intermittent conditions. Refer to Testing for Intermittent Conditions and Poor Connections .

Symptom List

Refer to HVAC System Malfunction (C60), HVAC System Malfunction (C67), HVAC System Malfunction (C41) in order to diagnose the symptom:

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