For 1990-2009 cars

The powertrain control module (PCM) controls the air conditioner (A/C) clutch by controlling an internal driver which pulls the A/C relay coil circuit to ground. The PCM monitors the relay coil circuit for low and high voltage faults. DTC P0647 sets when the A/C relay is being commanded ON and the voltage at the PCM is high.

### DTC Parameters

DTC P0647 will set if the A/C relay voltage is greater than 1.25 volts when the A/C relay is being commanded ON.

DTC P0647 diagnostic runs continuously with the engine running and the A/C relay commanded ON.

DTC P0647 is a type D DTC.

### Diagnostic Aids

To locate an intermittent problem, use a Scan tool to command the A/C RELAY ON, while monitoring the A/C RELAY-HIGH VOLT test. When a fault , shorted to voltage or shorted to solenoid exists, the Scan tool will display TEST FAIL.

The test will fail only when the device is being commanded ON and the voltage at the PCM is high. The tests update every 100 ms whenever the ignition is turned ON and the device is being commanded ON via the Scan tool or the PCM.

A/C relay coil resistance: 70-90 ohms.