What does it mean?
When a gasoline or diesel-powered vehicle runs, the fuel in the cylinder along with the oxygen in the air burns extremely hot. The gases produced in the combustion chamber are expelled in the exhaust stroke and sent through the exhaust pipe, destined for the atmosphere. Unfortunately, fuel in the cylinders doesn’t burn completely. The unburned fuel is carried along with the exhaust as it exits the engine.
These hydrocarbons are a major component of vehicle emissions and contribute to environmental pollution that can cause smog and exacerbate breathing issues. In addition to unburned hydrocarbons in the exhaust gases, a particularly harmful byproduct of excessive engine heat is NOx. It is produced in a narrow range of temperatures at the upper limit of engine combustion. The exhaust gas recirculation (EGR) system was developed to address these issues.
The EGR system reintroduces a portion of the engine’s exhaust gases back into the combustion process. This achieves two things: completely burning the hydrocarbons in the exhaust gas as well as diluting the air in the combustion chamber to reduce ignition temperatures. An EGR solenoid is used to meter the exhaust gases that are reintroduced into the engine.
It also prevents the EGR system from operating until the engine is at operating temperature, otherwise the engine will run rough on startup as it starves for oxygen-rich air. The EGR solenoid is typically mounted on the intake manifold. It uses engine vacuum to operate the EGR valve, which opens and closes to allow the exhaust gases into the intake. It receives 12-volt power from the powertrain control module when operating conditions — engine running and battery voltage above 12 volts — are met.
If the EGR solenoid circuit is not in the expected state when commanded by the PCM, DTC P0403 is set in the PCM and the Check Engine light is illuminated.