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 Sunshade - Left (D61)
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 KR29 A/C compressor clutch relay, ignition ON.
2. Verify a test lamp illuminates between the B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate and the circuit fuse is good
1. Ignition OFF.
2. Test for less than 2 ohms in the B+ circuit end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, verify the fuse is not open and there is voltage at the fuse.
• If the test lamp does not illuminate and the circuit fuse is open
1. Ignition OFF.
2. Test for infinite resistance between the B+ circuit and ground.
• If less than infinite resistance, repair the short to ground on the circuit.
• If infinite resistance,
3. Test for greater than 1 ohms between the control circuit terminal A and ground.
• If less than 1 ohms, repair the short to ground on the circuit.
• If greater than 1 ohms, test or replace the KR29 A/C compressor clutch relay.
• If the test lamp illuminates
3. Verify a test lamp illuminates between the ignition circuit terminal 85 and ground.
• If the test lamp does not illuminate
• Replace the X50A underhood fuse block.
• If the test lamp illuminates
4. Connect a test lamp between the ignition circuit terminal 85 and the control circuit terminal 86.
5. Verify the test lamp turns ON and OFF when commanding the 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 ECM, 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 ECM.
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 ECM.
• If the test lamp turns ON and OFF
6. Verify a test lamp does not illuminate between the control circuit terminal 87 and ground.
• If the test lamp illuminates
Repair the short to voltage on the circuit.
• If the test lamp does not illuminate
7. Ignition OFF and all vehicle systems OFF, disconnect the harness connector at the Q2 A/C compressor clutch.
8. Test for less than 10 ohms between the Q2 A/C compressor clutch ground circuit terminal B 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
9. Connect the harness connector at the Q2 A/C compressor clutch.
10. Ignition ON, connect a 30 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87.
11. Verify the Q2 A/C compressor clutch is activated.
• If the Q2 A/C compressor clutch does not activate
1. Ignition OFF.
2. Test for less than 2 ohms in the control circuit terminal 87 end to end.
• If 2 ohms or greater, repair the open/high resistance in the circuit.
• If less than 2 ohms, test or replace the Q2 A/C compressor clutch.
• If the Q2 A/C compressor clutch activates
12. Test or replace the KR29 A/C compressor clutch relay.
Repair Instructions
Perform the Diagnostic Repair Verification Verification Tests after completing the diagnostic procedure.
* HVAC Component Replacement Reference HVAC Component Replacement Reference
* Control Module References Control Module References for engine control module replacement, setup, and programming