The diagnosis trouble code P0003 has different meaning and it is based on the manufacturer of the cars and models. To know the meaning of the code, it is necessary to know the model and manufacturer. The code P0003 means exactly mentions to the camshaft (cam) timing. Power Steering Pressure Switch Malfunction in Key On, this DTC indicates the PSP input to the PCM and Engine Off Self-Test, is high. if the cam timing is over-retarded, the engine light will be illuminated and the code will be set. It is necessary to use manual of the car to know the detail meaning of the code.