EPHS power steering diagram (Electrically Powered Hydraulic Steering)
1 – steering gear housing; 2 – power steering sensor; 3 – steering column; 4 – instrument cluster control unit; 5 – speed sensor; 6 – engine control unit; 7 – Power steering indicator lamp; 8 – pressure main; 9 – return line; 10 – airbag control unit; 11 – pumping unit
a – signal to the power steering indicator lamp; b – crankshaft speed signal; in – vehicle speed signal; g – steering wheel speed signal; d – signal from the airbag control unit; e – contact 30; f – contact 15; z – "mass"
The amplifier is equipped with a gear pump driven by an electric motor. A receiver with valves, a pump and an electric motor form a pump unit. The power steering control unit, based on the steering wheel rotation speed, vehicle speed and crankshaft rotation frequency, regulates the volume of fluid supplied to the system by changing the rotation frequency of the pump drive electric motor shaft.
Protection is provided for turning on the pump unit in the event of a malfunction of the amplifier elements, the vehicle's on-board network, overheating of the pump unit, or a traffic accident. After the protection is triggered due to overheating of the pump unit, it can be disabled by turning off the ignition and restarting the engine after 15–20 minutes (to cool down the pumping unit).
In other cases, the protection must be disabled by clearing the contents of the fault memory (at the service station).
Please note: The steering gear cannot be repaired; if it malfunctions, it must be replaced as a complete unit. When replacing the steering gear, disconnect the steering rods from it (see subsection 8.5.4).