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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) 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/System Description

When the A/C switch is pressed, the HVAC control assembly sends a serial data message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CLTCH relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.

Conditions for Running the DTC

* The ignition voltage is between 9 and 18 volts.

* The engine speed is more than 600 RPM.

* An A/C request is made.

Conditions for Setting the DTC

* A short to ground on the A/C compressor clutch relay control circuit.

* A short to voltage on the A/C compressor clutch relay control circuit.

* An open circuit on the A/C compressor clutch relay control circuit or relay.

* An internally shorted or excessively low resistance A/C clutch relay coil.

Action Taken When the DTC Sets

* The A/C clutch relay is commanded OFF.

* The conditions for which the DTC was set will be stored in the Failure Records data only. No information will be stored as Freeze Frame data.

Conditions for Clearing the DTC

The history DTC will clear after 40 fault-free ignition cycles.

Reference Information

Schematic Reference

HVAC Schematics HVAC - Manual

Connector End View Reference

Component Connector End Views 1-2 Shift Solenoid (SS) Valve (MN5)

Description and Operation

* Air Delivery Description and Operation Air Delivery

* Air Temperature Description and Operation Air Temperature

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

2. Remove the control circuit terminal 46 using the correct terminal release tool, connect the X1 harness connector to the X50A fuse block-underhood.

3. Connect a test lamp between the control circuit terminal 46 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 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

7. Connect a test lamp between the control circuit terminal B 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.

Component Testing

1. Ignition OFF, disconnect the A/C COMP relay.

2. Test for 60-180 ohms between terminals 85 and 86.

• If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

* 30 and 86

* 30 and 87

* 30 and 85

* 85 and 87

• If not the specified value, replace the relay.

4. Install a 30-amp fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.

• If greater than the specified range, replace the relay.

Repair Instructions

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

* Air Conditioning Compressor Replacement (L4) Air Conditioning Compressor Replacement (L4)Air Conditioning Compressor Replacement (V6) Air Conditioning Compressor Replacement (V6)

* Relay Replacement (Within an Electrical Center) Relay Replacement (Within an Electrical Center)Relay Replacement (Attached to Wire Harness) Relay Replacement (Attached to Wire Harness)

* Control Module References Programming and Relearning for HVAC control module and ECM replacement, setup, and programming

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