P0645

DTC P0645

CIRCUIT DESCRIPTION
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.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
- DTC P0645 A/C Clutch Relay Control Circuit.

CONDITIONS FOR RUNNING THE DTC
- The ignition must be ON and the voltage must be between 9-18 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

Steps 1-11:

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.