Diagnostic Instructions
| • | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure. |
| • | Review Strategy Based Diagnosis for an overview of the diagnostic approach. |
| • | Diagnostic Procedure Instructions provides an overview of each diagnostic category. |
DTC Descriptor
DTC P0645: Air Conditioning (A/C) Clutch Relay Control CircuitDiagnostic Fault Information
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
|---|---|---|---|---|
A/C Relay Coil Ignition | 2 | 2 | -- | -- |
A/C Relay Switch B+ | 2 | 2 | -- | -- |
A/C Relay Control | P0645 | P0645 | P0645 | -- |
A/C Clutch Control | 2 | 2 | 1 | -- |
A/C Compressor Clutch Ground | -- | 2 | 2 | -- |
1. A/C Clutch Always Engaged 2. A/C Clutch Inoperative | ||||
Circuit Description
When the A/C switch is pressed, the HVAC control assembly sends a GMLAN message to the engine control module (ECM) for an A/C request. This input will request the ECM to ground the A/C compressor clutch relay control circuit, which will switch the A/C CMPRSR relay. With the relay contacts closed, battery voltage is supplied to the A/C compressor clutch assembly.
Conditions for Running the DTC
| • | The ignition voltage is between 11-18 volts. |
| • | The engine speed is less than 600 RPM. |
| • | The ECM driver transitions from ON to OFF or from OFF to ON. |
Conditions for Setting the DTCs
The ECM detects an open on the control circuit of the A/C compressor clutch relay when commanded off with the engine in crank or run status.
Action Taken When the DTC Sets
The ECM will store conditions which were present when the DTC set as Failure Records data only. This information will not be stored as Freeze Frame data.
Conditions for Clearing the DTC
| • | A History DTC clears after 40 consecutive warm-up cycles have occurred without a malfunction. |
| • | The DTC can be cleared by using a scan tool. |
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Electrical Information Reference
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Testing
- Ignition OFF, disconnect the A/C CMPRSR relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 86 and ground.
- Verify that a test lamp illuminates between the ignition circuit terminal 85 and ground.
- Connect a test lamp between the ignition circuit terminal 85 and thecontrol circuit terminal 86.
- Command the A/C relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If all circuits test normal, test or replace the A/C CMPRSR relay.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to ground. |
| ⇒ | If the test lamp does not illuminate, test the ignition circuit for a short to ground or an open/high resistance. If the circuit tests normal and ignition circuit fuse is open, test or replace the relay. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM. |
| ⇒ | 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 ECM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
