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.
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.
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
Written by Ken Lavacot 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 2009-08-25 (Updated 2015-01-07)