Audi Workshop Service and Repair Manuals

The EPHS (Electrically Powered Hydraulic Steering) system is governed by steering angle velocity and vehicle speed. The electrohydraulic steering is similar to the conventional power steering. The control unit, the hydraulic unit (electric motor and gear pump) and the hydraulic fluid reservoir form one unit, known as the motor/pump assembly, which cannot be dismantled.

This unit is not driven via the engine, but rather by an electric motor integrated into the motor/pump assembly.
Low steering angle velocity and high vehicle speed result in a low hydraulic fluid delivery rate and thus firm steering. When parking, vehicle speed is low and steering angle velocity high, thus producing light steering. The great advantage of this steering system is that it saves fuel, as energy consumption is based on actual requirements and is not dependent on the operating status of the engine.

Power steering sensor signals, vehicle speed signals and engine speed signals are transmitted to the power steering control unit -J500, which regulates the speed of the electric motor and thus the hydraulic fluid delivery rate.

Diagnostic communication is effected by way of the CAN. The gateway transfers the signals from the CAN to the K-wire. The self-diagnosis relates to the electrical section of the power steering. The control unit detects faults during vehicle operation and stores them in the dash panel insert (address word 17) in a non-volatile memory so that the information is retained even in the absence of battery voltage. Faults may take the form of defects in the electrical system. In the event of a fault entry, a yellow warning lamp lights in the dash panel insert display and the steering switches to a programmed emergency running mode. In this process, the steering function is retained but steering becomes slightly heavier. An acoustic warning signal is also given (1 beep).