Auxiliary Fan Control ('99 Model Year - E39): Notes

The Auxiliary Fan motor incorporates and output final stage that activates the fan motor at variable speeds.

The auxiliary fan is controlled by ECM. The motor output stage receives power and ground and activates the motor based on a PWM signal (10-100 Hz) received from the ME 7.2.

The fan is activated based on the following factors:

Fig 1: Identifying Auxiliary Fan Motor

Courtesy of BMW OF NORTH AMERICA, INC.

Radiator outlet temperature sensor input exceeds a preset temperature.
IHKA signalling via the K and CAN bus based on calculated refrigerant pressures.
Vehicle speed
Battery voltage level

When the over temperature light in the instrument cluster is on (120°C) the fan is run in the overrun function. This signal is provided to the ECM via the CAN bus. When this occurs the fan is run at a frequency of 10 Hz.

Fig 2: Auxiliary Fan Control Function

Courtesy of BMW OF NORTH AMERICA, INC.