P0647
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 ([1][2]Electrical Diagrams)
Connector End View Reference
Component Connector End Views (Connector Views)
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 (Programming and Relearning)
Circuit/System Verification
Ignition ON, command the A/C Compressor Clutch Relay ON and OFF with a scan tool. Feel/listen for the A/C relay to click.
Circuit/System Testing
1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 85 and ground.
• If the test lamp illuminates, test the control circuit for a short to voltage.
3. Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground.
• If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance.
4. Verify that a test lamp illuminates between the relay B+ circuit terminal 30 and ground.
• If the test lamp does not illuminate, test the B+ circuit for a short to ground or a open/high resistance.
5. Disconnect the harness connector at the Q2 A/C Compressor Clutch.
6. Test for less than 5 ohm between the Q2 A/C Compressor Clutch ground circuit terminal A and ground.
• If greater than the specified range, test the ground circuit for an open/high resistance.
7. Connect the harness connector at the Q2 A/C Compressor Clutch.
8. Connect a 10 A fused jumper wire between the B+ circuit terminal 30 and the control circuit terminal 87. Verify the Q2 A/C Compressor Clutch is activated.
• If the Q2 A/C Compressor Clutch does not activate, test the control circuit for an open/high resistance. If the circuit tests normal, test or replace the Q2 A/C Compressor Clutch.
9. Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
10. Command the A/C Compressor Clutch Relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
• If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the K20 Engine Control Module.
• If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the K20 Engine Control Module.
11. If all circuits test normal, test or replace the KR29 A/C Compressor Clutch Relay.
Component Testing
Static Test
1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 60-180 ohm between terminals 85 and 86.
• 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.
4. Install a 3 A fused jumper wire between relay terminal 86 and 12 V. Install a jumper wire between relay terminal 85 and ground. Test for less than 5 ohm between terminals 30 and 87.
• If greater than the specified range, replace the KR29 A/C Compressor Clutch Relay.
Repair Instructions
Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning)