Circuit Description

WARNING: This page is about a different car, the 2006 Pontiac Montana SV6, 2006 Chevrolet Uplander, and 2006 Buick Terraza. 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 powertrain control module (PCM) or engine control module (ECM) 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 PCM/ECM. When the PCM/ECM is commanding a component ON, the voltage of the control circuit should be near 0 volts. When the PCM/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, a DTC will set.

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

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