HVAC - Manual
DTC P0645
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 Descriptor
DTC P0645
- Air Conditioning (A/C) Compressor Clutch Relay Control Circuit
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
The ECM detects a short to ground or an open at the A/C compressor clutch relay control circuit.
Action Taken When the DTC Sets
The A/C compressor is inoperative or always active.
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 (Connector End Views By Name)
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)for scan tool information
Circuit/System Testing
1. Ignition OFF, remove the KR29 A/C Compressor Clutch Relay.
2. Ignition ON, test for greater than 11V between the ignition circuit terminal 86 at the KR29 A/C Compressor Clutch Relay and ground.
• If less than the specified value, test the ignition circuit for a short to ground or an open/high resistance.
3. Ignition OFF, disconnect the X1 harness connector at the K20 Engine Control Module.
4. Ignition ON, test for less than 0.3V between the control circuit terminal 85 at the KR29 A/C Compressor Clutch Relay and ground.
• If greater than the specified value, test the control circuit for a short to voltage.
5. 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 value, test the control circuit for a short to ground.
6. Test for less than 5 ohm between the KR29 A/C Compressor Clutch Relay control circuit terminal 85 and the control circuit terminal 32 X1 at the K20 Engine Control Module.
• If greater than the specified value, test the control circuit for an open/high resistance.
7. 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.
Component Testing
Static Test
1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 60-180 ohm 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 (Verification Tests) after completing the diagnostic procedure.
Control Module References (Programming and Relearning)for engine control module replacement, setup, and programming