P0646

DTC P0646

Circuit Description

The following DTCs are for the A/C compressor clutch relay:

^ DTC P0646 A/C clutch relay control circuit low voltage.
^ DTC P0647 A/C clutch relay control circuit high voltage.

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) controls the relay by grounding the control circuit via an internal solid state device called a driver. The primary function of the driver is to supply the ground for the component being controlled. Each driver has a fault line which is monitored by the ECM. When the ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be near battery voltage. If the fault detection circuit senses a voltage other than what is expected, this DTC will set.

Conditions for Running the DTC

^ The ignition must be ON and the voltage must be between 9.0-18.0 volts.
^ The ECM driver is activated or deactivated.

Conditions for Setting the DTC

^ The ECM detects an improper voltage level on the output circuit that controls the A/C relay.
^ The condition is present for at least 5 seconds.

Action Taken When the DTC Sets

^ The ECM will not illuminate the malfunction indicator lamp (MIL).
^ The ECM will not store Freeze Frame or Failure Records.
^ The A/C compressor clutch is disabled for the ignition cycle.

Conditions for Clearing the DTC

^ The DTC will become history if the ECM no longer detects a failure.
^ The history DTC will clear after 40 fault-free ignition cycles.
^ The DTC can be cleared with a scan tool.

Test Description

The numbers below refer to the step numbers on the diagnostic table.

2. Listen for an audible click when the A/C compressor clutch relay operates. Command both the ON and OFF states. Repeat the commands as necessary.
3. Tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies power to the coil side of the A/C compressor clutch relay.
4. Verifies that the engine control module is providing ground to the A/C compressor clutch relay. If light always on circuit shorted to ground.
8. Tests for a short to voltage or an open.
10. If the A/C fuse is open ensure to test the A/C compressor clutch supply voltage circuit for short to ground.