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• | 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. |
Circuit | Short to Ground | Open/High Resistance | Short to Voltage | Signal Performance |
---|---|---|---|---|
B+ | P0646 | P0647 | P0647 | -- |
Control | P0646 | P0647 | P0647 | -- |
The engine control module (ECM) controls the A/C compressor clutch based on an A/C request message from the HVAC control module. The ECM 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, 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.
• | The engine is running. |
• | The DTC runs continuously when the above conditions are met. |
• | The engine is running. |
• | The A/C relay is commanded ON. |
• | The DTC runs continuously when the above conditions are met. |
• | DTC P0562 or P0563 is not set. |
• | The engine is running. |
• | The ignition voltage is between 11-16V. |
• | The DTC runs continuously when the above conditions are met. |
The ECM detects a short circuit to ground or an open/high resistance on the A/C clutch relay control circuit.
The ECM detects a short circuit to voltage on the A/C clutch relay control circuit.
DTC P0646 and P0647 are Type C DTCs.
DTC P0646 and P0647 are Type C DTCs.
Manual HVAC Description and Operation
Powertrain Diagnostic Trouble Code (DTC) Type Definitions
Control Module References for scan tool information.
Engine running, command the A/C Relay On and OFF with a scan tool. The Q2 A/C Compressor Clutch should engage and disengage.
⇒ | 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 K20 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 K20 ECM. |
⇒ | If not within the specified range, replace the KR29 A/C Compressor Clutch Relay. |
• | 30 and 86 |
• | 30 and 87 |
• | 30 and 85 |
• | 85 and 87 |
⇒ | If not within the specified range, replace the KR29 A/C Compressor Clutch Relay. |
⇒ | If greater than the specified range, replace the KR29 A/C Compressor Clutch Relay. |
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
Control Module References for ECM replacement, setup, and programming.
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