May 19, 2023 / by Danny Mavis

For any car to work, there needs to be the combustion of air, consisting of roughly 80 per cent nitrogen and 20 per cent oxygen, and depending on the engine type, either diesel or petrol. This takes place at high temperatures, at which nitrogen and oxygen bond to produce one of the most toxic gases, nitrogen oxide. Not only is this a pollutant, but too much will affect your car’s fuel use and how it performs. Different engine management and exhaust system parts have gradually been fitted to cars to solve these issues, from OPF filters in petrol cars and DPF filters in diesels. But one component that now features in both is the Exhaust Gas Recirculation or EGR valve. This is one part that has a crucial role in reducing overall emissions and also helps the engine in a few significant ways.

What are EGR Valves?

This aptly named car part helps to reduce nitrogen oxides (NOx) by recirculating part of the exhaust fumes back into the combustion chamber before they exit the car through the exhaust system. NOx is a dangerous pollutant, responsible for a range of respiratory illnesses, and has a negative environmental impact by increasing greenhouse gases. The working principle of a car EGR valve is fairly simple. It helps cool exhaust gases, thereby preventing the high temperatures at which NOx forms. The valve is located between the exhaust and intake manifolds and can be in an open or closed position, depending on the engine temperature.

car egr valve

When starting the car, the EGR valve is closed and remains so until optimal working temperatures, generally around 90 degrees, are reached. A small portion of gases (5 to 15%) then are redirected back into the intake for re-burning, reducing the oxygen content and temperatures by almost 150 degrees. This has a knock-on effect in lowering NOx levels and additionally aids fuel use. The engine is not only more efficient, but the lower temperatures mean a healthier engine. When engine speeds and temperatures fall, say when turning the car off or when idling, the EGR returns to the closed position.

Types of EGR Valves

Your vehicle will be fitted with an EGR valve that is compatible with the type of engine and the fuel it uses. Generally, this means either a diesel or petrol valve, as the two fuel types combust at different temperatures and compression ratios. Diesel variants can be further divided into high and low-pressure valves, and work in slightly different ways. In the first type, the exhaust gases are harvested before entering the turbine and reintroduced in the intake manifold after the compressor.

This can put more strain on the engine internals due to the higher pressure involved, in addition to related parts in the EGR system such as the EGR cooler located between the turbine and valve and tasked to further cool things down. Better efficiency is achieved with low-pressure systems in which the exhaust gas is taken after the turbine and reintroduced into the intake manifold before the compressor, allowing for better flow, cleaner exhaust gases, and a reduced risk of soot buildup and strain on other parts.

Petrol EGR valves work much like the high-pressure diesel types in that the vacuum created by cylinder depression draws the exhaust gases in, and the flow is regulated by the opening and closing of the EGR valve.

egr system

In terms of how they operate and are controlled, EGR valves can be of two basic types – vacuum-operated and digital types. The first is the early designs to appear with the first batch of emissions standards, well before the advent of electronic management systems. This uses a vacuum diaphragm and a solenoid to open or close the valve.

The design has been refined over the years, with pulse width modulated solenoids for more precision. A digital car EGR valve is what is found on most vehicles today, using either solenoids, stepper, or brushless torque motors that open and close the valve irrelevant of the pressure and gas flow in the system, but is controlled from input by the ECU, which constantly monitors the EGR position.

Common EGR Issues and Symptoms

The high pressures and temperatures EGR valves work in means they are susceptible to wear and tear, particularly from soot buildup that can clog tubes and exhaust gas channels and damage the plunger mechanism, meaning it gets stuck in a closed or open position. Moreover, a ruptured or leaking valve diaphragm will also shoot up quite a few issues.

Typical signs that there is a fault with your car’s EGR valve are loss of power, hesitant acceleration, and rough idling caused by the valve stuck open and negatively impacting fuelling. This can be accompanied by a loss of boost pressure in the turbo. A faulty EGR valve will also have a harder time in redirecting exhaust gases, so emissions will be higher too.

With the valve in a stuck position, drivers can also notice somewhat higher fuel use than usual. In extreme cases, there are odd smells that point to unburnt fuel and the risk of pronounced engine vibrations and pre-detonation. The last issue may cause serious damage to spark plugs, piston rings, bearings, and head gaskets (among other parts), so getting your EGR valve cleaned or replaced on time will save you money and unwanted engine problems in the long run.