Troubleshooting in exhaust gas recirculation system on Otto and diesel engines

Vehicle: all vehicles equipped with exhaust gas recirculation system Products: Pos. 2, 3, 5, 6, 7 (see figure)

Exhaust gas recirculation (EGR) is a reliable and practice-proven method of emission control: As a result of exhaust gas, the oxygen content in the air-fuel mixture is reduced, and consequently the combustion temperature in the cylinders lowered. Since harmful nitrogen oxides (NOx) are mainly produced at high temperatures and pressures, it is possible to reduce the NOx concentrates emitted to the environment by up to 50%. On diesel engines, the formation of soot particulates is lowered by approx. 10%.
Exhaust gas recirculation is only activated at defined operating points. On petrol engines this is normally the case above idling and up to upper part load, on diesel engines up to approx. 3000 rpm and medium load.

EGR at a glance	Diesel engine (all injection types)	Petrol engine (manifold injection)	Petrol engine (direct injection)
Effects	Nitrogen oxides -50% Particulates -10% Less hydrocarbons emitted Less noise emitted	Nitrogen oxides -40% Fuel consumption -3% Less CO2	Nitrogen oxides -50…60% Fuel consumption -2% Less CO2
Return rates	Max. 65%	Max. 25%	Max. 50% (with stratifi ed charge) Max. 30% (with homogenous operation)
Others	EGR cooling is required for vehicles with higher weight class	EGR cooling under discussion	High EGR rates at high load

The EGR valve meters the amount of recirculated exhaust gas.
It is added either at the exhaust manifold or at the intake air system, or it is located in a heatresistant exhaust-gas pipe which connects the exhaust manifold to the intake air system. Pneumatic EGR valves are actuated by way of vacuum via electromagnetic valves:
On basic systems with an electric switchover valve, the EGR valve only has an open-close function.
On systems provided with an electro-pneumatic pressure transducer (EPW), the EGR valve is infinitely adjustable.
The vacuum is taken from the intake manifold or generated by a vacuum pump. Electric or electromotive EGR valves are actuated direct by the control unit and no longer need any vacuum or solenoid valve.