P0646
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 Electrical Diagrams
Connector End View Reference
Component Connector End Views Fuel Pump and Level Sensor Assembly
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 86 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 86 and the control circuit terminal 85.
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 repair.
* HVAC Component Replacement Reference Removal and Replacement
* Control Module References Control Module References for engine control module replacement, programming, and setup