For 1990-2009 cars

### 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 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 | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance
--- | --- | --- | --- | ---
A/C Compressor Clutch Relay Coil Ignition | P0646 | P0645, P0646 | -- | --
A/C Compressor Clutch Relay Coil Control | P0646 | P0645, P0646 | P0647 | 1
1. A/C Compressor Malfunction

### 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

#### Connector End View Reference

Component Connector End Views

#### Description and Operation

Manual HVAC Description and Operation

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### Scan Tool Reference

Control Module References for scan tool information

### Circuit/System Testing

1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay and the X2 harness connector at the K20 Engine Control Module (ECM).
2. Ignition ON, test for greater than 11 V between the ignition circuit terminal 85 at the KR29 A/C Compressor Clutch Relay and ground.

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

3. Test for less than 0.3 V between the control circuit terminal 86 at the KR29 A/C Compressor Clutch Relay and ground.

⇒ | If greater than the specified range, test the control circuit for a short to voltage.

4. Ignition OFF, test for infinite resistance between the control circuit terminal 86 at the KR29 A/C Compressor Clutch Relay and ground.

⇒ | If less than the specified range, test the control circuit for a short to ground.

5. Test for less than 5 Ω between the KR29 A/C Compressor Clutch Relay control circuit terminal 86 and the appropriate control circuit terminal at the K20 Engine Control Module (ECM) harness connector listed below:

• | Terminal 4 (X2) with LDE

• | Terminal 11 (X2) with LLU

• | Terminal 4 (X2) with 2H0

• | Terminal 44 (X2) with LDK

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

6. If all circuits test normal, test or replace the KR29 A/C Compressor Clutch Relay and verify the DTC does not reset.

⇒ | If the DTC resets, replace the K20 Engine Control Module (ECM).

### Component Testing

#### Static Test

1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 60-180 Ω 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 after completing the diagnostic procedure.

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