Auxiliary Fan Control
Using a 99 MY vehicle (E38/39/46) for this test, the variable auxiliary fan is controlled by the ECM. The auxiliary fan request comes from the IHKA control module via the K-Bus. The fan speed request is based on the refrigerant pressure sensor input to the IHKA. Additional factors monitored by the ECM that influence fan operation are:
- Radiator outlet temperature sensor (exceeds the preset temperature)
- Vehicle speed
- Battery voltage level
The auxiliary fan motor incorporates an output final stage that activates the fan motor at variable speeds. The output stage receives an output signal (pulse width modulated 10-100 Hz) from the ECM which activates the motor.