Circuit Description

WARNING: This page is about a different car, the 2004 Pontiac Grand Prix. However, it is still accessible from the selected car via links, so may be relevant.

DTC P0480 low speed cooling fan relay control circuit
DTC P0481 high speed cooling fan relay control circuit

Battery positive voltage is supplied to the fan 1 relay from the FAN 1 fuse. The powertrain control module (PCM) controls the fan 1 relay by grounding the low speed cooling fan relay control circuit through an internal solid state device called a driver.

Battery positive voltage is supplied to the fan 2 relay and the fan relay from the FAN 2 fuse. The PCM controls the relays by grounding the high speed cooling fan relay control circuit.

When the PCM is commanding a relay on, the voltage potential of the control circuit should be low, near 0 volts. When the PCM is commanding the control circuit to a relay, 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
An open relay coil
An internally shorted or excessively low resistance relay coil

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