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 Descriptors
DTC P0645: Air Conditioning (A/C) Clutch Relay Control CircuitDTC P0646: Air Conditioning (A/C) Clutch Relay Control Circuit Low Voltage
DTC P0647: Air Conditioning (A/C) Clutch Relay Control Circuit High Voltage
Diagnostic 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, P0646 | P0645, P0647 | P0645, P0647 | -- |
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/System Description
When the A/C switch is pressed, the HVAC control assembly sends a serial data 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 CLTCH 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 9 and 18 volts. |
| • | The engine speed is more than 80 RPM. |
| • | The ECM A/C Compressor Clutch Relay Control transitions between ON to OFF or from OFF to ON. |
Conditions for Setting the DTC
| • | A short to ground on the A/C compressor clutch relay control circuit. |
| • | A short to voltage on the A/C compressor clutch relay control circuit. |
| • | An open circuit on the A/C compressor clutch relay control circuit or relay. |
| • | An internally shorted or excessively low resistance A/C clutch relay coil. |
Action Taken When the DTC Sets
| • | The A/C clutch relay is commanded OFF. |
| • | The conditions for which the DTC was set will be stored in the Failure Records data only. No information will be stored as Freeze Frame data. |
Conditions for Clearing the DTC
The history DTC will clear after 40 fault-free ignition cycles.
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 COMP relay.
- Ignition ON, verify that a test lamp does not illuminate between the control circuit terminal 85 and ground.
- Verify that a test lamp illuminates between the ignition circuit terminal 86 and ground.
- Connect a test lamp between the ignition circuit terminal 86 and the control circuit terminal 85.
- 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 COMP relay.
| ⇒ | If the test lamp illuminates, test the control circuit for a short to voltage. |
| ⇒ | 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. |
Component Testing
- Ignition OFF, disconnect the A/C COMP relay.
- Test for 60-180 ohms between terminals 85 and 86.
- Test for infinite resistance between the following terminals:
- Install a 30A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 ohms between terminals 30 and 87.
| ⇒ | If the resistance is not within the specified range, replace the relay. |
| • | 30 and 86 |
| • | 30 and 87 |
| • | 30 and 85 |
| • | 85 and 87 |
| ⇒ | If not the specified value, replace the relay. |
| ⇒ | If greater than the specified range, replace the relay. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM setup, replacement, and programming
