Circuit Description

WARNING: This page is about a different car, the 2007 Saturn Vue. However, it is still accessible from the selected car via links, so may be relevant.

Ignition voltage is supplied directly to the A/C compressor clutch relay. The engine control module (ECM) or powertrain control module (PCM) controls the relay by grounding the A/C clutch relay 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. The driver has a fault line which is monitored by the ECM/PCM. When the ECM/PCM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the ECM/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, a DTC will set.

The ECM/PCM will monitor the control circuit for the following:

A short to ground
A short to voltage
An open circuit
An open relay coil
An internally shorted or excessively low resistance relay coil

When the ECM/PCM detects any of the above malfunctions, a DTC is set and the affected driver is disabled.