Electric Cooling Fan
The 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 .
The PCM also adjusts the electric cooling fan speed to compensate the ram effect of vehicle speed.
The PCM varies the duty cycle of the PWM signal to the engine cooling fan control module between 0 and 100%. This operates the electric cooling fan motor in 1 of 4 modes:
- Off
- Minimum speed
- Linear variable speed between minimum and maximum speeds
- Maximum speed.
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. In case of any faults detected, the engine cooling fan control module temporarily pulls the PWM signal to ground. This notifies the PCM about the fault. 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 seconds intervals until the fault is cleared. If there is more than 1 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(s) (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 HMI systems bus to the IPC to display a warning message.
The nominal operating voltage for the electric cooling fan is from 9 V to 16 V. If the input voltage is outside of these limits, the engine cooling fan control module stops operation of the electric cooling fan. In addition it 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 V, or decreases to 15.5 V, respectively.
Each time, the engine cooling fan control module checks the electric cooling fan motor speed. This is 2 seconds after the electric cooling fan receives power supply. If the speed is 0, the engine cooling fan control module determines the electric cooling fan motor is stalled and tries a restart. The engine cooling fan control module disconnects the power from the electric cooling fan motor then immediately reconnects, with an increased current level.
The engine cooling fan control module tries up to 6 restarts of a stalled motor, increasing the output current each time. If the electric cooling fan motor remains stalled after the 6 restart, the engine cooling 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 electric cooling fan is running the engine cooling fan control module monitors the current draw against electric cooling 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 electric cooling fan motor.
- Then 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:
| 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 (PWM relay fuse may blow) | Off |