HVAC System - Manual

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.

DTC DESCRIPTOR
This diagnostic procedure supports the following DTC:
DTC P0645 Air Conditioning (A/C) Clutch Relay Control Circuit

CONDITIONS FOR RUNNING THE DTC
- The ignition voltage is between 9-18 volts.
- The engine speed is more than 80 RPM.
- The PCM driver is activated.

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 not present, refer to Testing for Intermittent Conditions and Poor Connections in Diagnostic Aids.

TEST DESCRIPTION

Steps 1 - 13:

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. This step tests for voltage at the coil side of the A/C compressor clutch relay. The 10-amp fuse supplies ignition 1 voltage to the coil side of the A/C compressor clutch relay.
4. This step verifies that the PCM is providing ground to the A/C compressor clutch relay.
5. This step tests if ground is constantly being applied to the A/C compressor clutch relay.
6. This step tests for a short to voltage or an open.
12. Perform the programming procedure for the PCM.