Engine Cooling Fans
The Powertrain Control Module (PCM) determines when to operate the electric cooling fan
- The input from the Engine Coolant Temperature (ECT) sensor
- And a cooling fan request from the HVAC Control Module.
The PCM also adjusts the fan speed to compensate 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.
Viscous Cooling Fan
To control the viscous cooling fan, the PCM sends a Pulse Width Modulation (PWM) signal to the Viscous Cooling Fan Control Module (VCFCM). The PCM varies the duty cycle of the PWM signal between 0 and 100% to vary the clutch engagement and thus fan speed.
If the PWM signal is out of the range
- The VCFCM interprets the signal as an open or short circuit
- And runs the fan at minimum speed to make sure that the fan does not overspeed.
If the electrical connections to the viscous fan are disconnected the fan will idle and the engine may overheat. The PCM records a related Diagnostic Trouble Code (DTC) for faults notified by the VCFCM and signals the BCM/GWM through the FlexRay bus. The BCM/GWM transmits the signal on the HS CAN chassis systems bus to the IC to display a warning message.
Electric Cooling Fan
The PWM signal could be between 0 and 100% to operate the fan motor in 1 of 4 modes:
- Off
- Minimum speed - 750 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 the engine cooling fan control module detects any of these faults then pulls the PWM signal to ground to notify 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 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 through the FlexRay bus. The BCM/GWM transmits the signal on the HS CAN comfort systems bus to the IC to display a warning message.
The nominal operating voltage for the engine cooling fans is 9 to 16V. If the input voltage is outside of the limits, the engine cooling fan control module stops the cooling fan and notifies the PCM of the fault. After an under or over voltage occurs, cooling fan operation is resumed when the input voltage increases to 9.5V, or decreases to 15.5V, respectively.
When the fan control module supplies power to start the electric cooling fan the control module checks the cooling fan motor speed after 2 seconds. If the speed is zero, the fan control module determines the fan motor is stalled and tries a restart. For a restart, the fan control motor disconnects the power from the fan motor then immediately reconnects it at an increased current level. The fan control module will try up to 6 restarts of a stalled motor, increasing the output current each time.
If the fan motor remains stalled after the sixth restart
- The fan control module waits 40 seconds then notifies the PCM of the fault
- And begins the start process again.
To check for a partially stalled motor, while the fan is running the fan control module monitors the current draw against fan speed.
If the current draw is over the limit for more than 10 seconds
- The fan control module disconnects the power from the fan motor
- And notifies the PCM of the fault.
After 40 seconds, the fan control module starts the motor again.
The fan control module incorporates a temperature sensor to prevent damage caused by excessive heat at high ambient temperatures. Operation of the 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:
| SIGNAL | FAULT | FAN SPEED | |
|---|---|---|---|
| IGNITION ON | IGNITION OFF | ||
| PWM | Duty cycle implausible | Maximum | Off |
| PWM | Frequency out of range | Maximum | Off |
| PWM | Open circuit | Maximum | Off |
| PWM | Short circuit to battery | Maximum (provided cooling fan is not damaged) | Off |
| PWM | Short circuit to ground | Maximum (provided cooling fan is not damaged) | Off |
| Ignition | Open circuit | Off | Off |
| Ignition | Short circuit to battery | According to PWM duty cycle | Maximum |
| Ignition | Short circuit to ground | Off (PCM relay fuse may blow) | Off |