"Small Cooling Fan" in order to prevent the engine control unit generates the PWM signal line to ground or short to power, when the cooling fan control unit detects that the PWM signal is 0 V or 12 V, the cooling fan control unit controls the fan at maximum speed will often turn . "Small Cooling Fan" control unit operating power supply unit is powered by the engine control relay (J271). Cooling fan working power is often provided by the 30th line of fire. When the ignition switch is turned off, the engine control unit is still working when the engine control unit detects the coolant temperature is too high and needs to cool down, to "Small Cooling Fan" control unit sends a PWM signal, the cooling fan control unit may continue to operate .