General Information

Engine Control
P0646 A/C Clutch Relay Control Circuit Low - General Information

Component Location





General Description

The A/C clutch relay is activated if the A/C switch is operated while the blower is running and system operation is enabled by the ECM. When A/C is requested, the Engine Control Module(ECM) provides a ground path to the A/C clutch relay control circuit. When the relay circuit is grounded, the A/C clutch relay is energized. The ECM delays grounding the relay circuit for a short time, so the ECM can adjust the engine idle speed for the additional load. The ECM will temporarily de-energized the A/C clutch relay for one or more of the following conditions:
-Full acceleration when the throttle is at WOT.(Wide Open Throttle)
-Risk of overheating : Engine coolant temp. exceeds threshold value
-A/C system pressure exceeds threshold value
-Engine starting

DTC Description

If there is Short to ground in A/C Relay circuit, ECM sets DTC P0646.

DTC Detecting Condition





Diagnostic Circuit Diagram