The Exhaust Gas Recirculation (EGR) system is monitored by a vacuum solenoid. Once the power switch is activated, the solenoid is supplied with power. The Power Train Control Module (PCM) supervise the vacuum solenoid and the control circuit will connect to ground.
The main function of this controller is provide ground to the controller. The Powertrain Control Module (PCM) monitors each of the controllers’ circuits to determine possible faults. When one of these components is turned on by the PCM, the expected voltage in the circuit must be zero. The voltage should be high or close to the battery voltaje, if the parts are switched off. The PCM observes these two conditions before, in case you don’t see the proper voltage at that time, the DTC code P0403 OBD2 is established.