P0645

Schematic:

CIRCUIT DESCRIPTION
A voltage is supplied directly to the A/C compressor clutch relay coil. The PCM controls the relay by grounding the control circuit via an internal switch called a driver. The primary function of the driver is to supply the ground for the controlled component. Each driver has a fault line which the PCM monitors. When the PCM commands a component ON, the voltage of the control circuit should be low (near 0 volts). When the PCM is commanding the control circuit to a component OFF, the voltage potential of the circuit should be high (near battery voltage). If the fault detection circuit senses a voltage other than what the circuit expects, the fault line status changes causing the DTC to set.

The relay controls the high current flow to the A/C compressor clutch. This allows the PCM driver to only have to handle the relatively low current used by the relay.

CONDITIONS FOR RUNNING THE DTC
^ The engine speed is greater than 400 RPM.
^ The ignition voltage is between 6.0 volts and 18.0 volts.

CONDITIONS FOR SETTING THE DTC
^ The PCM detects that the commanded state of the driver and the actual state of the control circuit do not match.
^ Condition must exist for a minimum of 5 seconds.

ACTION TAKEN WHEN THE DTC SETS
^ The PCM stores the DTC information into memory when the diagnostic runs and fails.
^ The Malfunction Indicator Lamp (MIL) will not illuminate.
^ The PCM records the operating conditions at the time the diagnostic fails. The PCM stores this information in the Failure Records.

CONDITIONS FOR CLEARING THE MIL/DTC
^ A last test failed (current DTC) clears when the diagnostic runs and does not fail.
^ A History DTC clears after 40 consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures.
^ Use a scan tool in order to clear the MIL/DTC.

DIAGNOSTIC AIDS

IMPORTANT:
^ Remove any debris from the PCM connector surfaces before servicing the PCM. Inspect the PCM connector gaskets when diagnosing/replacing the PCM. Ensure that the gaskets are installed correctly. The gaskets prevent contaminate intrusion into the PCM.
^ For any test that requires probing the PCM or a component harness connector, use the Connector Test Adapter Kit J 35616-A. Using this kit prevents damage to the harness/component terminals. Refer to Using Connector Test Adapters in Diagrams.

For an intermittent condition, refer to Symptoms. Symptom Related Diagnostic Procedures

TEST DESCRIPTION

Steps 1 - 9:

Steps 10 - 15:

The numbers below refer to the step numbers on the diagnostic table.
2. Listen for an audible click when the relay operates. Command both the ON and the OFF states. Repeat the commands as necessary.
4. This step tests for voltage at the coil side of the A/C relay. The A/C Cruise mini fuse supplies power to the coil side of the A/C relay.
5. This step verifies that the PCM is providing ground to the A/C relay.
6. This step tests if ground is constantly being applied to the A/C relay.