HVAC - Manual

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 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 an A/C request message to the engine control module (ECM) via CAN-Bus. Therefore, the ECM grounds the A/C compressor clutch relay control circuit, which will switch the A/C compressor clutch relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch. The A/C compressor clutch will be activated.

Conditions for Running the DTC

* Engine is running.
* The HVAC control module is ON.
* The A/C switch is active.

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

The condition for setting the DTC is no longer present.

Reference Information
Schematic Reference

HVAC Schematics (HVAC - Manual)
Connector End View Reference

Component Connector End Views (Connector End Views By Name)
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 (Programming and Relearning) for scan tool information

Circuit/System Testing

1. Ignition OFF, remove the KR29 A/C Compressor Clutch Relay.
2. Ignition ON, test for greater than 11 V between the ignition circuit terminal 86 at the KR29 A/C Compressor Clutch Relay and ground.

• If less than the specified value, test the ignition circuit for a short to ground or an open/high resistance.

3. Ignition OFF, disconnect the X2 harness connector at the K20 Engine Control Module.
4. Ignition ON, test for less than 0.3 V between the control circuit terminal 85 at the KR29 A/C Compressor Clutch Relay and ground.

• If greater than the specified value, test the control circuit for a short to voltage.

5. Ignition OFF, test for infinite resistance between the control circuit terminal 85 at the KR29 A/C Compressor Clutch Relay and ground.

• If less than the specified value, test the control circuit for a short to ground.

6. Test for less than 5 ohm between the KR29 A/C Compressor Clutch Relay control circuit terminal 85 and the appropriate control circuit terminal at the K20 Engine Control Module harness connector listed below:

* Terminal 91 X2 with LXV
* Terminal 51 X2 with LXT
* Terminal 91 X2 with 2H0
* Terminal 29 X2 with LLW

• If greater than the specified value, test the control circuit for an open/high resistance.

7. If all circuits test normal, test or replace the KR29 A/C Compressor Clutch Relay.

Component Testing

Static Test
1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 60-180 ohm between the B+ terminal 85 and the control terminal 86 of the KR29 A/C Compressor Clutch Relay.

• If not within the specified range, replace the KR29 A/C Compressor Clutch Relay.

3. Test for the resistance between the following terminals:

* 30 and 86
* 30 and 87
* 30 and 85
* 85 and 87

• If not the specified value, replace the KR29 A/C Compressor Clutch Relay.

Repair Instructions

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

Control Module References (Programming and Relearning) for engine control module replacement, setup, and programming