Engine Cooling Fans
Each electric cooling fan is operated by a Pulse Width Modulation (PWM) signal from the Powertrain Control Module (PCM).
The PCM determines when to operate the cooling fan from the Engine Coolant Temperature (ECT) sensor input. A cooling fan request message from the Automatic Temperature Control Module (ATCM) will also instruct the PCM to activate the cooling fans. The PCM adjusts the fan speed by varying the PWM signal to the fans motors to compensate for the ram air cooling effect of vehicle speed.
Each electric cooling fan is provided with:
- A battery power supply from the Auxiliary Junction Box (AJB)
- An ignition signal from the PCM relay in the Engine Junction Box (EJB)
- A PWM signal from the PCM
- A ground.
Logic within the fan motors monitor for over and under input voltage, a stalled motor or a partially stalled motor. If any of these faults are detected the PWM signal from the PCM is pulled to ground to notify the fault to the PCM. The length of time the PWM signal is pulled to ground varies between two and eight seconds, depending on the fault. The notification process is repeated at five second intervals until the fault is cleared. If there is more than one fault, only the highest priority fault is notified to the PCM. Fault priorities, in descending order, are over voltage, under voltage, stalled motor and partially stalled motor. The PCM records a related Diagnostic Trouble Code (DTC) for faults notified by the logic within the fan motors. The PCM signals the Instrument Cluster (IC) on the High Speed (HS) Controller Area Network (CAN) HMI systems bus to display a warning message.
For additional information, refer to: ENGINE COOLING