Electric Cooling Fan

The Powertrain Control Module (PCM) determines when to operate the electric cooling fan from the Engine Coolant Temperature (ECT) sensor input and a cooling fan request from the HVAC control module (HVAC). The PCM also adjusts the fan speed to compensate for the ram effect of vehicle speed.

The PCM varies the duty cycle of the Pulse Width Modulation (PWM) signal to the engine cooling fan control module. It is varied between 0 and 100% to operate the fan motor in one of four modes:

• Off
• Minimum speed - 750 Revolutions Per Minute (RPM)
• Linear variable speed between minimum and maximum speeds
• Maximum speed - 2820 RPM

Under hot operating conditions, the electric cooling fan may continue to operate for up to 5 minutes after the engine has been switched off.

The engine cooling fan control module monitors for over and under input voltage, a stalled motor and a partially stalled motor. If it detects any of these faults the engine cooling fan control module temporarily pulls the PWM signal to ground. This action notifies the fault to the PCM. The length of time the PWM signal is pulled to ground varies between 2 and 8 seconds, depending on the fault. The engine cooling fan control module repeats the notification process at 5 second intervals until the fault is cleared. If there is more than one fault, only the highest priority fault is notified to the PCM.

The fault priorities in descending order are the following:

• Over voltage
• Under voltage
• Stalled motor
• Partially stalled motor.

The PCM records a related Diagnostic Trouble Code (DTC) for faults notified by the engine cooling fan control module and signals the BCM/GWM assembly through the FlexRay bus. The BCM/GWM assembly transmits the signal on the High Speed (HS) Controller Area Network (CAN) comfort systems bus to the IC to display a warning message. For additional information, Refer to: INFORMATION AND MESSAGE CENTER

The nominal operating voltage for the electric cooling fan is 9 to 16 Volts. If the input voltage is outside of these limits, the engine cooling fan control module stops operation of the electric cooling fan and notifies the PCM of the fault. After an under or over voltage occurs, the electric cooling fan operation is resumed when the input voltage increases to 9.5 Volts, or decreases to 15.5 Volts, respectively.

To check for a stalled motor, each time it supplies power to start the electric cooling fan the engine cooling fan control module checks the cooling fan motor speed after 2 seconds. If the speed is zero, the engine cooling fan control module determines the cooling fan motor is stalled and tries a restart. For a restart, the engine cooling fan control motor disconnects the power from the cooling fan motor then immediately reconnects it at an increased current level. The engine cooling fan control module will try up to six restarts of a stalled motor, increasing the output current each time. If the fault remains, the engine cooling fan control module waits 40 seconds then notifies the PCM of the fault and begins the restart process.

To check for a partially stalled motor, while the electric cooling fan is running the engine cooling fan control module monitors the current draw against fan speed. If the current draw is over the limit for more than 10 seconds, the engine cooling fan control module disconnects the power from the cooling fan motor. Afterwards, it notifies the PCM of the fault. After 40 seconds, the engine cooling fan control module starts the motor again.

The engine cooling fan control module incorporates a temperature sensor to prevent damage caused by excessive heat at high ambient temperatures. Operation of the engine cooling fan control module is discontinued if the temperature reaches 135°C (275°F). Operation resumes when the temperature decreases to 120°C (248°F).

If a fault occurs with the ignition signal or the PWM signal, the engine cooling fan control module adopts the following fan speeds: