Circuit Description

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora and 2001 Oldsmobile Aurora. However, it is still accessible from the selected car via links, so may be relevant.

Battery positive voltage is supplied to the cooling fan s/p relay and the cooling fan 2 relay from the cool fan 2 fuse. The powertrain control module (PCM) controls the relays by grounding the high speed cooling fan 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. Each driver has a fault line which is monitored by the PCM. When the PCM is commanding a component on, the voltage potential 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 is expected, the DTC will set.

The PCM will monitor the control circuit for the following:

A short to ground
A short to voltage
An open circuit

When the PCM detects any of the above conditions, the DTC will set and the affected driver will be disabled.