P0645

DTC P0645

Circuit Description

Ignition voltage is supplied directly to the A/C compressor clutch relay. The powertrain control module (PCM) 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 PCM. When the PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the PCM 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 voltage is between 9.0-18.0 volts.

Conditions for Setting the DTC

- The PCM detects an improper voltage level on the output circuit that controls the A/C relay.
- The condition is present for at least 30 seconds.

Action Taken When the DTC Sets

- The PCM will not illuminate the malfunction indicator lamp (MIL).
- The PCM stores the failure records.
- The A/C compressor clutch is disabled.

Conditions for Clearing the DTC

- The DTC will become history if the PCM 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.

Diagnostic Aids

If condition is intermittent refer to Testing for Intermittent Conditions and Poor Connections.

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 powertrain control module is providing ground to the A/C compressor clutch relay.
5. Tests if ground is constantly being applied to the A/C compressor clutch relay.
6. Tests for a short to voltage or an open.
12. Perform the recalibration procedure for the powertrain control module.