Introduction
An EGR (exhaust gas re-circulation) valve is designed to lower NOX (NO2) gases that occur in the combustion chamber when temperatures reach over 3,500 degrees Fahrenheit. NOX gases have been proven to cause brain damage in humans, therefore EGR valves have been mandatory on most vehicles since 1976. An EGR valve controls exhaust gases and allows them to enter the intake manifold and flow into the combustion chamber at certain times in the operation of the vehicle to reduce combustion chamber temperatures.
Electrically Operated EGR Valve (Linear)
To test your vacuum operated EGR valve remove the vacuum line that is connected to the valve, apply vacuum using a vacuum pump to the valve while the engine is running. If the engine stalls the EGR system is working, if not, the EGR valve may have failed or the passages may be plugged with carbon deposits. Testing of a Linear (electric) EGR valve requires a scan tool capable of applying the valve on command.
Source by:
http://www.2carpros.com/how_does_it_work/how_an_egr_valve_works.htm
