ELECTRIC COOLING FAN
There are 2 variable speed electric cooling fans housed in the cooling fan shroud for cooling of the radiator. The speed of the electric cooling fans are adjusted by the cooling fan motor control module, which is controlled by the Engine Control Module (ECM).
The ECM determines the cooling fan speed by receiving inputs from the Engine Coolant Temperature (ECT) sensor and the Dual Automatic Temperature Control (DATC) module. The ECM sends a variable Pulse Width Modulated (PWM) signal to the fan motor control module to operate the cooling fans at the required speed. The cooling fans are operated at slow speed when the engine coolant temperature is at 203 F (95 C) and are operated at full speed when the engine coolant temperature is at 221 F (105 C). A coolant temperature between these temperatures will cause the cooling fans to be operated at a speed which is proportional to the engine coolant temperature.
When the engine is running with the ECT above 212 F (100 C), if the ignition switch is turned to the OFF position the cooling fans will continue to operate for a time which is determined by the ECM. The ECM will continue to control the fan speed to provide an extended period of cooling as required to protect the engine. The ECM will remain on and obtain a run-on time from a pair of "look-up maps". The fan speed PWM signal is maintained for the duration of the run-on time. At the end of the time period, the cooling fans will be turned off and then the ECM turns off. Maximum time is 6 minutes and 40 seconds.
If the PWM signal from the ECM to the cooling fan control module is 7-95 percent, the cooling fan control module will operate the cooling fans at the required speed. If the PWM signal from the ECM to the cooling fan control module is below 3 percent and above 95 percent, the cooling fan control module will operate the cooling fans at maximum speed. If the PWM signal from the ECM to the cooling fan control module is between 3-7 percent, the cooling fans will not be operated.
Saturday, October 31st, 2009 AT 7:49 PM