DTC P0403: EGR Solenoid Control Circuit: Description
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2003 Pontiac Grand Prix, 2003 Pontiac Bonneville, 2003 Chevrolet Monte Carlo, 2003 Chevrolet Impala, and 2003 Buick Regal. 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.