Electric Cooling Fan

WARNING: This page is about a different car, the 2003 Pontiac Vibe. However, it is still accessible from the selected car via links, so may be relevant.

The engine cooling fan system consists of an electric cooling fan, two fan relays and a fan resistor. The fan 1 relay controls power to the fan motor. The fan 2 relay controls the ground path of the fan motor. The gauge fuse supplies ignition voltage to the coils of both the fan 1, and the fan 2 relays. The RDI fuse supplies battery voltage to the switch side of the fan 1 relay. The PCM controls the ground for the coils of both relays. The PCM controls low and high speed fan operation by energizing and de-energizing the fan 2 relay which changes the ground path of the fan motor.

During low speed operation, which is when the A/C is operating and the Engine Coolant Temperature (ECT) is below 181°F (83°C), the PCM supplies the ground path for the fan 1 relay through the cooling fan 1 relay control circuit. This energizes the relay, closes the fan 1 relay contacts, and supplies battery voltage from the RDI fuse through the cooling fan motor supply voltage circuit to the fan motor. The ground path for the fan motor is through the closed contacts of the de-energized fan 2 relay, through the fan resistor to ground point G103. The result is a series circuit with the fan running at low speed.

During high speed operation, which is when the ECT reaches 199°F (93°C) or the A/C system pressure exceeds 220 psi (1520 kPa), the PCM supplies the ground path for the fan 1 relay through the cooling fan 1 relay control circuit. This energizes the relay, closes the fan 1 relay contacts, and supplies battery voltage from the RDI fuse through the cooling fan motor supply voltage circuit to the fan motor. The PCM also supplies the ground path for the fan 2 relay. This energizes the relay, switches the fan 2 relay contacts, and supplies a ground for the fan motor directly to ground point G103. The result is a series circuit with the fan running at high speed.

The A/C refrigerant pressure switch is in parallel with the PCM controlled ground for the coil of the fan 2 relay. If the A/C system pressure exceeds 220 psi (1520 kPa), the pressure switch closes the ground circuit to the coil of the fan 2 relay, initiating high speed fan operation.

The PCM commands low speed fan operation when all of the following conditions occur:

A/C system is operating.
A/C system pressure is below 178 psi (1226 kPa).
Engine Coolant Temperature (ECT) is below 181°F (83°C).

The PCM commands high speed fan operation when either of the following conditions occur:

ECT reaches 199°F (93°C).
A/C system pressure exceeds 220 psi (1520 kPa).

For component application and related wiring, see ELECTRIC COOLING FANS - 1.8L VIBE article in ENGINE COOLING.