What Is An Exhaust Gas Recirculation (EGR) Valve?

The Exhaust Gas Recirculation (EGR) system is designed to reduce harmful nitrogen oxides in the emissions. Nitrogen Oxide (NOx) is an irritant that can cause lung damage if people are exposed to it for long periods of time. The EGR valve recycles some of the exhaust gases back into the engine. The gases reduce the temperature in the engine, so less harmful gases are produced. Most cars require the EGR system to meet emission standards, although some engines are now designed not to need them at all.

What happens when the EGR valve fails?

With exhaust gasses constantly flowing through it, you can imagine the EGR valve isn’t too pretty. Eventually, it sticks and clogs with all of the soot from the exhaust leaving the valve open or closed. A check engine light should be illuminated for either case.

An EGR valve that is open continuously will have a constant flow of gases into the engine, meaning the car will idle rough and stall. You will also notice the MPG come down and more fuel in the emissions, which you can smell. The lower temperatures will also fail your emissions test in an MOT.

A constantly closed EGR valve may cause the fuel to ignite early, as the temperature is higher. This means you’ll hear pinging at low RPM, then loud bangs as you rev your engine. The bangs will leave you with some extensive engine repairs that are very costly so don’t ignore them. It will also fail your MOT, with the high NOx emissions.