Engine Cooling Fan: Operation

All electric cooling fans operate when engine coolant temperature exceeds a certain value. The ECM completes ground path for the cooling fan relay. Relay contacts then close and complete circuit between fusible link and fan motor. When the engine cools, the relay opens and fan stops. If coolant sensor fails, the ECM will command constant fan operation.

A/C-equipped vehicles have a separate signal line to the Electronic Control Module (ECM) for fan control. When A/C control switch is on, and A/C system low pressure switch is closed, ECM receives a signal on this line and turns cooling fan on. The A/C compressor clutch does not have to engage for ECM to turn fan on.

On some models, the ECM may turn on fan relay and run fan for up to 7 minutes when engine is off. This occurs if hot conditions were present while engine was running. Hot conditions are based on Manifold Absolute Temperature (MAT) signal to ECM, coolant temperature and time from start.