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Exhaust Gas Recirculation (EGR) what is it? How does it work? be Aware of the risks!

  • Lexicon
  • 4 min read
Close-up of the old exhaust gas recirculation (EGR).

What is Exhaust Gas Recirculation?

The valve is just one component of Exhaust Gas Recirculation, or in simple translation, the exhaust gas recirculation system. In general, it’s a system designed to divert a portion of the exhaust gas into the engine’s intake system and thereby reduce the oxygen content delivered to the combustion chamber. To learn more about the emission standards overall click here.

The ultimate goal is to reduce the emissions of harmful substances in the exhaust gas that exits through the exhaust pipe into the atmosphere. Integrated into the vehicle’s engine management system, the EGR valve recirculates precisely measured amounts of exhaust gas into the engine’s intake system to increase engine efficiency, reduce fuel consumption and lower NOx emissions.


On some engines, variable valve timing is also part of the Exhaust Gas Recirculation system. This is a so-called internal implementation of exhaust gas recirculation, which involves opening the exhaust valve earlier, resulting in some of the exhaust gas backing up into the intake system. The external implementation is the use of the popular EGR valve, discussed in this article.

For what is it responsible and how does it work?

The purpose of using the EGR valve is to reduce the oxygen content of the air supplied to the combustion chamber, thereby reducing the temperature and slowing down the combustion process, as well as reducing nitrogen oxide (NOx) emissions. The effect of reducing the amount of oxygen in the combustion chamber is realized by adding an appropriate portion of the exhaust gas to the intake system, which, in a nutshell, contaminates the air supplied to the chamber.

Why the valve breaks down?

The most common cause of a valve failure is contamination. Heavy contamination makes it difficult for the control elements to work, leading to failure. A high risk is also associated with the aggressive effect of exhaust gases on EGR valve components, so it is not uncommon to burn out the material inside the valve. Due to the aggressive nature of the exhaust gas, the material inside the EGR valve is burned off.

Is the EGR valve an operational part?

Even if some of the controls fail, it usually happens due to wear and tear. Since it gets dirty and that is the main cause of problems, it should be considered a consumable part, and thus periodically replaced/cleaned. Click here for tips on cleaning the EGR.

Since the valve operates in an unfavorable environment, this causes wear and tear over time. The most common cause of failure is the accumulation of “dirt” or carbon particles. It is obvious that over time such action will simply clog the pipe and the entire exhaust duct.

To minimize the release of nitrogen oxides into the atmosphere, the valve allows a certain amount of exhaust gas to be reintroduced into the intake system, effectively changing the chemical composition of the air entering the engine. The Exhaust Gas Recirculation valve has two basic settings: open (idle and low speeds) and closed (during engine startup)

Symptoms of EGR problems

What to look for in a failing EGR valve?

Due to the fact that EGR valve problems are humanly similar to those associated with engine management components, it becomes quite a puzzle for technicians or mechanics. Fortunately, there are several signs that we can easily pick up on problems:

  • Check engine light
  • Engine performance problems: if the EGR is blocked, the vehicle’s air/fuel ratio will be altered, causing engine performance problems (reduced power, poor acceleration and rough idling)
  • Increased NOx emissions: when the EGR remains closed, excessive temperature in the combustion chamber accumulates, leading to increased NOx emissions and reduced fuel efficiency.
  • Engine knocking (associated with higher temperatures)