Mechanics

EGR Valve

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Step by step instructions on how an automotive EGR valve works. This article pertains to all exhaust gas recirculation equipped engines.

Step 1 - 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. There are different types of valves such as electrically operated EGR (linear) and vacuum operated valves.


EGR Valve

Step 2 - To test a vacuum operated EGR valve, remove the vacuum line that is connected to the valve, apply vacuum using a vacuum pump while the engine is running. The engine should stall or stumble if the EGR system is working, if not, the passages that connect the valves exhaust port through to the intake manifold could be clogged or the valve plunger has failed, the valve must be removed to check for these conditions. To test the operation of a linear (electric) EGR valve requires a scan tool capable of applying commands to the valve.

Helpful Information

An EGR valve also helps cool combustion temperatures to stem engine detonation or pinging while the engine is under load. The operation of the valve begins while engine vacuum is lowered due to throttle position and declines as maximum vacuum returns (idle.) Carbon can build up along the valve passages so occasional maintenance is recommended.

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AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-11-21)