Ford Kuga

 Service Manual

Power Steering » Power Steering (System Operation and Component Description)
System Operation

Electronic principle of operation

The power steering module requires the following information in order to ensure precise steering behavior in all driving situations:

• Steering wheel position
• Rate of turn of the steering wheel
• Vehicle speed
• Information about the vehicle configuration
• Information about the ignition switch position
• Instantaneous engine operating status

The required information is made available to the power steering module via direct connections and via the CAN bus (refer to the flow chart).

The steering wheel position and the rate of turn of the steering wheel are transmitted to the power steering module as PWMsignals from the steering angle sensor. The steering angle sensor receives its voltage and ground supply from the power steering module and operates inductively with an input voltage of 5 V.

The vehicle speed is made available to the power steering module as a CAN bus signal from the ABS module or ESP module.

The engine operating status is made available to the power steering module as a CAN bus signal from the PCM.

The power steering module obtains the vehicle configuration information via the CAN bus from the GEM. This information is required by the power steering module in order to define the internal characteristics of the power steering.

The power steering module obtains information about the current ignition switch position via the voltage input (terminal 15) of the ignition switch.

Whilst constantly monitoring the relevant input signals the power steering module accesses stored maps. With the aid of this information the pump speed is matched to the current driving situation.

An electronic diagnosis of the electro-hydraulic power steering can be performed with the aid of a diagnostic tester via the DLC of the vehicle. For additional information please refer to "Diagnosis and Testing" in this section.

Hydraulic principle of operation

When the engine is started, the electro-hydraulic power steering pump sucks in power steering fluid from the reservoir. The fluid flows through the pump and is discharged under high pressure from the outlet. The high-pressure line carries the power steering fluid to the servo valve.

If no steering effort is applied, there is no resistance to the circulation of power steering fluid and the supply pressure from the pump is very low. Only minimal pressure is applied by the servo valve to the two sides of the piston in the working cylinder.

When the steering wheel is turned in either direction, the return flow of fluid to the reservoir is restricted by the servo valve, causing the pressure to increase on the supply side. The power steering fluid is directed by the servo valve to the corresponding side of the piston in the working cylinder, providing the power assistance required to reduce the steering effort. The power steering fluid which is displaced towards the low-pressure side of the cylinder flows through the servo valve and the return line back to the reservoir.

System Diagram

System Operation

Component Description