DTC P0403: EGR Valve Control Circuit: Description
WARNING: This page is about a different car, the 2003 Cadillac Seville and 2003 Cadillac DeVille. However, it is still accessible from the selected car via links, so may be relevant.
The Powertrain Control Module (PCM) controls the Exhaust Gas Recirculation (EGR) valve with a solid state device called a driver. The driver supplies the EGR solenoid with 12 volts that is Pulse Width Modulated (PWM) through the EGR solenoid high control circuit. A ground path is provided by the PCM through the EGR solenoid low control circuit. The driver has the ability to detect an electrical malfunction on the EGR solenoid control circuits. If the PCM determines that the driver has detected an electrical malfunction on one of these circuits, DTC P0403 sets.