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 P0646: Air Conditioning (A/C) Clutch Relay Control Circuit Low VoltageDTC 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 B+ | P0646 | P0647 | P0647 | -- |
A/C Compressor Clutch Relay Control | P0646 | P0647 | P0647 | -- |
Circuit/System Description
The engine control module (ECM)/powertrain control module (PCM) controls the A/C compressor clutch based on an A/C request serial data message from the HVAC control module. The ECM/PCM monitors the A/C refrigerant pressure sensor and if pressure is within a specified range, will engage the A/C compressor by grounding the A/C compressor clutch relay control circuit.
B+ is applied to the A/C relay in the RUN/START position and with the A/C compressor clutch relay control circuit grounded by the ECM/PCM, current flows through the coil side of the A/C relay. With current flowing through the coil side of the relay, a magnetic field is created which pulls the switch side of the relay closed, sending current to the A/C compressor clutch, allowing the A/C compressor to be engaged.
Conditions for Running the DTC
An A/C request is received from the HVAC module.
Conditions for Setting the DTC
A short to voltage, short to ground, or open/high resistance is seen on the A/C compressor clutch relay control circuit.
Action Taken When the DTC Sets
DTC P0646 and DTC P0647 are Type C DTCs
Conditions for Clearing the DTC
DTC P0646 and DTC P0647 are Type C DTCs
Reference Information
Schematic Reference
Connector End View Reference
Description and Operation
Air Temperature Description and Operation
Electrical Information Reference
| • | Circuit Testing |
| • | Wiring Repairs |
DTC Type Reference
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Scan Tool Reference
Control Module References for scan tool information
Circuit/System Verification
Engine running, command the A/C Relay On and OFF with a scan tool. The A/C compressor clutch should engage and disengage.
Circuit/System Testing
- Ignition OFF, disconnect the A/C relay.
- Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal and ground.
- Connect a test lamp between the relay coil B+ circuit terminal and the A/C compressor clutch relay control circuit terminal.
- Engine running, command the A/C relay ON and OFF. 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 relay.
| ⇒ | If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. |
| ⇒ | If the test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM/PCM. |
| ⇒ | 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/PCM. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM/PCM replacement, setup, and programming
