Cooling Fan Description and Operation (LM2)

Cooling Fan Control The engine cooling fan system is composed of 3 electric cooling fans. Each fan motor assembly contains an integral cooling fan control module. The cooling fan control modules communicates with the engine control module (ECM) independently, via a local interconnect network (LIN). The ECM controls the fan speed of each fan by sending a digital signal to the cooling fan control modules over two different serial data circuits. The cooling fan control modules decode the respective signals and control the voltage drop across the cooling fan motor with a pulse width modulated (PWM) signal in relation to the speed request. This allows each of the cooling fans to operate at variable speeds independent of each other. Each cooling fan and module is programed to its location within the system. If the cooling fans are not connected to their specific connector, the fans will operate with out a DTC, but there will be noise or performance issues that will occur. The cooling fans will not operate at equal speeds for a given cooling fan command to prevent unwanted noise or vibration. The cooling fan speed is affected by many different conditions and the ECM will adjust the duty cycle from 0–100 percent based on cooling system requirements. The actual commanded cooling fan speed is based on a number of inputs from the ECM, and cooling fan requests from other modules, such as the BCM, TCM, and HPCM, if equipped. When multiple cooling fan speed requests are received, the ECM commands the cooling fan control module to operate the fan at the highest requested speed. The scan tool Cooling Fan Request Source parameter identifies the predominant sub-system requiring cooling fan operation. The scan tool output control is only capable of operating the cooling fan in increments between 10–90 percent. 90 percent is considered high speed. The increments and ranges found within the scan tool function may vary from vehicle to vehicle. The ECM commands the fan On under the following conditions: The engine coolant temperature is warmer than a predetermined temperature. The engine oil temperature is warmer than a predetermined temperature. The A/C pressure reaches a predetermined pressure. If the engine coolant temperature at key-off is warmer than a predetermined value, or the A/C pressure is greater than a predetermined value, the cooling fan will operate at a low speed. The fan will shut OFF if the temperature or pressure drops below the predetermined value, but will only operate for 2 minutes, regardless of the coolant temperature or A/C pressure.