5.19.1 Description

The electric cooling fan is PWM driven by the ECM. The PWM signal duty cycle is dependent upon the temperature of the bottom hose coolant temperature sensor.

There are two diagnostic checks on the output signal from the ECM: -

1. An electrical check where the ignition is on and the fan is activated. A short to battery positive, short to ground or open circuit condition can be detected.
2. An electrical check where the ignition is on and the fan is not activated. A short to battery positive, short or open circuit condition can be detected.
   Fan Control
   
   

   Component/System	Fault Codes	Monitoring Strategy Description	Malfunction Criteria	Threshold value	Secondary Parameter	Enable Conditions	Time Required	MIL Illumination
   Engine Cooling  Fan Signal Line	P1671 P1670	Circuit voltage Circuit voltage	Short to battery positive or ground or open circuit Short to battery positive or open circuit	Ignition key Ignition key					On & Fan Activated On & Fan not Activated	10 sec	No MIL illumination

If the above table does not include details of the following enabling conditions: - IAT, ECT, vehicle speed range, and time after engine start-up then the state of these parameters has no influence upon the execution of the monitor.