Although there are several designs of EGR (Exhaust Gas Recirculation) systems, they all work similarly. The Exhaust Gas Recirculation (EGR) valve is controlled by the PCM (Powertrain Control Module) and in this way, the amount of exhaust gas, which is to be burned with the air/fuel mixture, can be measured. As this gas is very inert and displaces oxygen, when it is injected back into the cylinder, it helps to reduce temperature and nitrogen oxide emission.
The Exhaust Gas Recirculation (EGR) valve and the PCM are connected directly to each other electrically via a group of wires, usually 4 or 5 wires. Two of these are 12-volt ignition power cables, one for a 5-volt reference circuit, and one for a feedback circuit. The feedback circuit allows the Powertrain Control Module (PCM) to observe that the EGR valve clamp is performing its movements correctly. If the feedback loop detects that the voltage is low or the position it has commanded is not correct, the fault code P0405 OBD2 is set.