The Exhaust Gas Recirculation System (EGR) is built into diesel engine vehicles. The function of this system is to send exhaust gases to the engine induction system where they are converted to air. A cooling valve is included in the EGR, which controls the flow of engine coolant.
The Powertrain Control Module (PCM) receives constant signals from the EGR Coolant Temperature Sensor (ECT) and the EGR Cooler Temperature Sensor to determine the times at which the cooling valve opens and closes. If the voltages from these sensors are inconsistent with those programmed into the PCM, the P2425 OBDII diagnostic code will be stored and the Check Engine service lamp will illuminate.