Cooling Fan Control
The engine cooling fan is a variable speed fan. The engine control module (ECM) controls the fan speed by sending a pulse width modulated (PWM) 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 10-90 percent duty cycle , 90 percent 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 fans ON under the following conditions:
| • | The engine coolant temperature goes above a calibrated amount. |
| • | The engine oil temperature goes above a calibrated amount. |
| • | The A/C pressure reaches a calibrated temperature. |
| • | After the engine is shut OFF, if the engine coolant temperature at key-off is greater than a calibrated amount, or the A/C pressure is greater than a calibrated amount, the cooling fan is set to low speed. The fan will shut OFF if the temperature
or pressure drops below a calibrated amount. The fans will shut OFF after 2 minutes, regardless of coolant temperature. |
