Cooling Fan Description and Operation

Cooling Fan Description and Operation

Cooling Fan Control - Variable Speed Single Fan System

The engine cooling fan is a variable speed fan. The ECM controls the fan speed by sending a pulse width modulated signal to the cooling fan control module. The cooling fan control module varies the voltage drop across the cooling fan motor in relation to the pulse width modulated signal.

Cooling fan speed is effected by many different conditions and can be adjusted from 10% to 90% duty cycle (PWM), 90% is considered high speed fan. When multiple cooling fan speed requests are received the ECM uses the highest cooling fan speed of all the requests. The ECM commands the cooling fan ON under the following conditions:

* Cooling fan duty cycle starts when engine coolant temperature reaches approximately 95°C (204°F) and reaches high speed at temperatures above 113°C (235°F).
* Cooling fan duty cycle starts when A/C pressure reaches approximately 1100 kPa (160 psi) and reaches high speed at A/C pressures above 2480 kPa (360 psi).
* At engine oil temperatures above approximately 150°C (302°F) the cooling fan duty cycle will be commanded to high speed.
* At transmission oil temperatures above approximately 132°C (270°F) the cooling fan duty cycle will be commanded to high speed.
* After the vehicle is shut OFF if the engine coolant temperature at key-off is greater than 113°C (235°F) or the A/C pressure is greater than 1720 kPa (249 psi) the cooling fan duty cycle is set to 50%, low speed. If the coolant temperature drops below 110°C (230°F) and the A/C pressure drops below 1660 kPa (241 psi) the fan will shut OFF. The fans will automatically shut OFF after 2 min. regardless of coolant temperature.