The power steering ECU (Electronic Control Unit) is a small electronic metal box which is located above the steering column assembly behind the dashboard. It is responsible for determining the amount of power-assist to use and the direction of power-assist when operating a vehicle. It works by assessing signals from the steering torque sensor and the speed of the vehicle through ABS and applying the correct amount of pressure to allow the driver to exert less effort when driving. Should the vehicle not have ABS, the power steering ECU relies on speed signals from the speedometer. This system replaced the original hydraulic system, which was slow and heavy and could cause dragging of the pump on the engine.
During its operation, the ECU controls the motor by rotating the steering gear pinion. Should the ECU become faulty, it will signal its error by communicating with the electronic warning system and a warning light will appear in the vehicle. Upon driving you will most likely experience very heavy steering which will usually be intermittent at first, but if left alone will become a permanent situation so a swift repair is necessary. A full ECU replacement may be required in this circumstance.