Steering Control Module: Description and Operation

The EHPS (electro hydraulic power steering) system functions to change the forces required for steering maneuvers, and thereby provide the ideal steering feeling for all the vehicle speeds and steering conditions. This is done by the power steering ECU, which controls the hydraulic pressure acting upon the hydraulic reaction chamber (located in the gear box control unit) by regulating the power steering motor's speed (and hence the amount of fluid flow).

EHPS OPERATION
When the ignition is switched on, starting current flows from the GAUGEfuse to TERMINAL IGB of the power steering ECU, TERMINAL VS of the steering position sensor, and TERMINAL A-4of the power steering driver.
The vehicle speed is detected by the speed sensor, and signals are input as control signals to TERMINAL SPD of the power steering ECU and to TERMINALS SS1 and SS2 of the power steering ECU.
When the engine is started, signals are input to TERMINAL EFI of the power steering ECU from TERMINAL PSCT of the engine control module (ECU) . As a result, the current applied to TERMINAL IGB of the power steering ECU from the GAUGE fuse flows from TERMINAL MRLY of the power steering ECU --> TERMINAL A-1 of the power steering relay --> TERMINAL A-2 --> GROUND, and the power steering relay is switched on. As a result, the current applied to TERMINAL B-1 of the power steering relay from the ABS fuse flows from TERMINAL B-2 of the power steering relay --> TERMINAL C-1 of the power steering driver and to TERMINAL A-1 of the power steering motor.
If the vehicle speed is low, the speed of the power steering motor is increased by increasing the voltage of the current that flows from TERMINAL A-1 of the power steering motor to TERMINAL A-2 of the power steering motor --> TERMINAL C-2 of the power steering driver --> TERMINAL B-2 --> GROUND, with the result that the volume of flow of the power steering fluid becomes greater, thus providing a light steering feeling.
When the vehicle speed is high, the speed of the power steering motor decreases as a result of the reduced voltage applied to the power steering motor, and thus the volume of flow of the power steering fluid is reduced, so the steering feeling is more resistant.