Spark

DTC P0646 or 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.

P0646 (Without FX3)

P0647 (Without FX3)

P0646 or P0647 (FX3)

P0646

The ECM detects a short circuit to ground or an open/high resistance on the A/C clutch relay control circuit.

P0647

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.

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Manual HVAC Description and Operation

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

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.

1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒	If the test lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect a test lamp between the relay coil B+ circuit terminal 85 and the relay control circuit terminal 86.
4. Ignition ON, 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 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.

5. If all circuits test normal, test or replace the KR29 A/C Compressor Clutch Relay.

1. Ignition OFF, disconnect the KR29 A/C Compressor Clutch Relay.
2. Test for 70--110 Ω of resistance between terminals 85 and 86.

⇒	If not within the specified range, replace the KR29 A/C Compressor Clutch Relay.

3. Test for infinite resistance between the following terminals:

•

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.

4. Install a 20A fused jumper wire between terminal 85 and B+. Install a jumper wire between relay terminal 86 and ground. Test for less than 2 Ω between terminal 30 and 87.

⇒	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.