Cooling System: Description and Operation

Cooling Fan Circuit:

DESCRIPTION
This vehicle uses an electric cooling fan. The fan is used for engine and A/C condenser cooling but the fan only operates under certain conditions.

OPERATION
The electric cooling tan operates when engine cooling temperature exceeds a certain value. The cooling fan on this engine is totally controlled by the Powertrain Control Module (PCM). The cooling fan has one speed. The PCM turns the cooling fan "ON" by grounding the coil of the cooling fan relay when certain conditions are met. When A/C is requested, the cooling fan will be turned "ON."

When vehicle speed is above 35 MPH, the PCM opens the ground to the cooling fan relay because there should be sufficient air moving through the radiator to cool the engine. If A/C refrigerant pressure or engine coolant temperature becomes excessive or the Malfunction Indicator Lamp (MIL) is illuminated, the PCM will turn the fan "ON" regardless of vehicle speed.

COOLING FAN RUN-ON
The PCM usually "powers down" 10 to 30 seconds after the ignition is turned "OFF." Since the cooling fan is PCM controlled, the PCM remains "powered up" for up to 7 minutes after the ignition is turned "OFF" to provide the ground to energize the fan relay.

This is called fan "Run-On" and will occur if any of the following combinations of conditions exist when the ignition is turned "OFF."

- Engine coolant temperature greater than 100°C and intake air temperature greater than 80°C.
- Engine coolant temperature greater than 112°C and intake air temperature greater than 70°C.
- Engine coolant temperature greater than 116°C.

The cooling fan will remain "ON" until these combinations of conditions no longer exist, up to a maximum of 7 minutes.

If the cooling fan is "OFF" when the PCM "powers down," after the ignition is turned "OFF," it will remain "OFF" regardless of temperatures, until the ignition is turned "ON" again.