Diagnostic Instructions

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

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

Automatic HVAC Description and Operation

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Circuit/System Testing

1. Ignition OFF, remove the KR29 A/C Compressor Clutch Relay and disconnect 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 86 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 85 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 85 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 85 and the appropriate control circuit terminal at the K20 Engine Control Module (ECM) harness connector listed below:

•	Terminal 91 (X2) with LXV

•	Terminal 29 (X2) with LLW

⇒	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

Control Module References