The power steering system consists of a steering pump, which is driven by a belt, a steering box, there are also hoses and sensors. The PCM (Powertrain Control Module) works in conjunction with the PSP (Power Steering Pressure) Sensor to control the system pressure and make adjustments accordingly.
The PCM illuminates the Check Engine light along with the diagnostic code P0551 OBDII when it finds one or more conditions that are outside the range of the power steering circuit and sensors. While this code is usually caused by electrical failures, mechanical problems are not excluded.