HVAC - Automatic
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 - Automatic)
Connector End View Reference
Component Connector End Views (Connector End Views By Name)
Description and Operation
Automatic HVAC Description and Operation (HVAC - Automatic)
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 11 V 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 0.3 V 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