Servo Unit

The servo unit provides active steering-effort assistance as required by steering force and vehicle conditions. The servo unit is located on the upper steering column and is protected in the passenger compartment, it consists of:

Electric Motor
Worm Gear
Control Unit
Internal sensors for electric motor speed, steering torque, temperature and voltage.
Coil-spring cassette for the internal steering torque sensor. See Fig 1 .

Fig 1: Identifying Servo Unit

Courtesy of BMW OF NORTH AMERICA, INC.

The electric motor and the worm gear in the servo unit produce a new acoustic pattern in the passenger compartment. The system acoustics can be heard in particular situations:

When the steering wheel is spun quickly.
When the steering wheel is turned while the car is stationary.
When the steering wheel is turned in a quiet atmosphere (e.g. radio not turned on).

This acoustic pattern is not a system fault. The conventional sounds generated by hydraulic steering systems (pump modulation, limiting valve) are eliminated. Note: The EPS Control Module cannot be replaced separately, the entire assembly with the exception of the Steering Angle Sensor must be replaced as a unit.