Engine management system - MEMS (Cooling Fans): Description and operation

Cooling Fans

The cooling system comprises an engine coolant cooling fan which is located behind the radiator and an engine bay cooling fan located in the engine bay. On vehicles fitted with A/C, an additional cooling fan is located behind the radiator and A/C condenser.

An engine bay cooling fan is located in the engine bay. The fan is used to reduce engine bay temperatures especially when the vehicle is stationary. The fan draws air through the RH air intake into the engine bay.

On all vehicles the engine bay cooling fan relay is located adjacent to the passenger compartment fusebox.

On vehicles without A/C, the engine cooling fan relay is located behind the under bonnet fusebox. On vehicles with A/C, the engine cooling fan relay and the condenser fan relay are located in the A/C relay module which is located adjacent to the under bonnet fusebox.

Engine Coolant Cooling Fan

The engine cooling fan relay is energised by the ECM on receipt of an appropriate coolant temperature signal from the ECT sensor.

When the engine is running, the ECM will energise the relay to operate the fan at a coolant temperature of 104°C (219°F) and will go off when the coolant temperature decreases to less than 98°C (208°F).

When A/C is fitted, the engine cooling fan and the condenser fan can operate at two speeds, being operated in series or parallel by the ECM. Refer to the Air Conditioning section for condenser fan details.

Engine Bay Cooling Fan

The engine bay cooling fan relay is energised by the ECM on receipt of an appropriate engine bay temperature signal from the ambient air temperature sensor.

When the engine is running, the ECM will energise the relay to operate the fan when an engine bay temperature of 75°C (167°F) is reached. The ECM has a timer which energises the relay for a predetermined period. If the temperature decreases to less than 60°C (140°F) before the timer has expired, the ECM will de-energise the relay.

If the engine bay temperature exceeds 130°C (266°F), the ECM will illuminate the engine bay overheat warning lamp in the instrument pack. The warning lamp informs the driver that the engine bay temperature is abnormally high or that a system fault has occurred. When the engine bay temperature falls below 110°C( 230°F) the ECM will extinguish the warning lamp.

When the engine is off, the fan remains active for a predetermined period after the engine is switched off.