The A/C clutch relay is located in the underhood fuse block (UHFB). The ECM controls the A/C clutch by supplying a ground to the A/C clutch relay. The ECM controls an internal driver is normally open and supplies a ground to the A/C clutch relay whenever the A/C clutch relay is commanded On. The A/C clutch relay control circuit is monitored for low and high voltage and open circuit faults. DTC P0646 will set if the ECM detects a feedback voltage below a calibrated value in the A/C clutch relay control circuit when the relay is commanded Off.

DTC P0646 will set if the ECM detects the A/C clutch relay control feedback voltage at the ECM is below 2.6 volts when the relay is being commanded Off when:

DTC P0646 diagnostic runs continuously with ignition On and A/C clutch relay commanded Off.

P0646 is a (type D) DTC

Inspect harness for chaffed wiring that may cause a short to ground condition on circuit 459.