HVAC - Manual

DTC P0645

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.

Circuit/System Description

When the A/C switch is pressed, the HVAC control module sends an A/C request message to the engine control module (ECM) via CAN-Bus. The ECM then grounds the A/C compressor clutch relay control circuit, closing the A/C compressor clutch relay contacts. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch and A/C compressor clutch is activated.

Reference Information

Schematic Reference

HVAC Schematics HVAC - Manual

Connector End View Reference

Component Connector End Views Outside Rearview Mirror - Driver

Description and Operation

Manual HVAC Description and Operation HVAC - Manual

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 Testing

1. Ignition OFF, disconnect the X3 harness connector at X50A fuse block-underhood.

2. Remove the control circuit terminal 34 using terminal release tool J-44020-4, connect the X3 harness connector to the X50 fuse block underhood.

3. Connect a test lamp between the control circuit terminal 34 and B+, engine running.

4. Verify the test lamp turns ON and OFF when commanding the Q2 A/C compressor clutch ON and OFF with a scan tool.

• If the test lamp is always OFF

1. Ignition OFF, disconnect the harness connector at the K20 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 K20 ECM.

• If the test lamp is always ON

1. Ignition OFF, disconnect the harness connector at the K20 Engine Control Module.

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, replace the K20 Engine Control Module.

• If the test lamp turns ON and OFF

5. Ignition OFF and all vehicle systems OFF, connect the harness connector at the X50A fuse block-underhood, disconnect the harness connector at the Q2 A/C compressor clutch. It may take up to 2 minutes for all vehicle systems to power down.

6. Test for less than 10 ohms between the Q2 A/C compressor clutch ground terminal 1 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

7. Connect a test lamp between the control circuit terminal 2 and ground.

8. Verify the test lamp turns ON and OFF when commanding the Q2 A/C compressor clutch ON and OFF with a scan tool.

• If the test lamp is always OFF and the circuit fuse is good

1. Ignition OFF, disconnect the X1 harness connector at the X50A fuse block-underhood.

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, replace the X50A fuse block-underhood.

• If the test lamp is always OFF and the circuit fuse is open

1. Ignition OFF

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, replace the Q2 A/C compressor clutch.

• If the test lamp is always ON

1. Ignition OFF, disconnect the X1 harness connector at the X50A fuse block-underhood, Ignition ON.

2. Test for less then 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, replace the X50A fuse block-underhood.

• If the test lamp turns ON and OFF

9. Replace the Q2 A/C compressor clutch.

Repair Instructions

Perform the Diagnostic Repair Verification Verification Tests after completing the repair.

* HVAC Component Replacement Reference Removal and Replacement

* Control Module References Control Module References for HVAC control module programming and setup