What are EGR valves?

The car world is full of technologies that few people know about, until they go wrong. Exhaust Gas Recirculation valves are typical examples.

What are EGR valves?

Fitted to both petrol and diesel cars, EGR valves are important anti-pollution devices that reduce nitrogen oxide (NOx) emissions. As NOx is a group of gases that is harmful to human health, vehicle manufacturers have been encouraged to fit EGR valves to improve air quality.

EGR valves control the flow of exhaust gases back into the engine's air inlet. While this seems to be a crazy idea, the spent exhaust gases have a cooling effect on the engine's cylinders. The reduced temperatures curtail NOx formation.

While most modern cars have one high-pressure EGR circuit, many vehicles that comply with Euro VI emissions standards have two. We shall investigate the difference between the two systems in another blog.

Do EGR valves have any advantages for me?

Apart from the air quality benefits, EGR can reduce both fuel consumption and CO2 emissions. For instance, when coasting in gear, with the throttle released, instead of the engine having to suck air into its cylinders via the air filter, introducing recycled exhaust gases instead introduces less drag and reduced pumping losses. The quantity of fuel injected can also be reduced under part-load conditions with the EGR valve open, with a corresponding reduction in emissions.

The reduced temperatures benefit other components, too, such as turbochargers.

What goes wrong?

Being a simple valve that regulates exhaust gas flow, EGR valves work in a hot and dirty environment. They can clog with sooty deposits that prevent the valve from opening and closing. While cleaning may be an option, consider that a typical EGR valve lifespan is 70,000 miles. Therefore, paying a garage to remove, clean and refit it may be a false economy, compared with renewing the worn part.

If operated electrically, the wiring and connectors can fail. If operated pneumatically, the rubber pipes can split and develop air leaks. Therefore, an EGR fault may not be a problem with the valve itself but another component that controls it.

What are EGR Coolers?

EGR coolers also fail. These are connected to the car's cooling system and cool the incoming exhaust gases before they reach the EGR valve. The reason is that cooler exhaust gases reduce engine cylinder temperatures even further, resulting in even larger NOx emission reductions. The picture heading this article shows a combined cooler and EGR valve.

To work effectively, exhaust gas heat energy transfers through the cooler's thin aluminium walls into the cooling system. Over time, the internals can corrode, causing engine coolant to enter the EGR valve, which then passes into the engine. The EGR cooler can also be damaged by insufficient air being bled from the system, whenever the antifreeze coolant is replaced.

The sooty exhaust gases can also block the cooler, restricting the quantity of gas reaching the EGR valve.

Why can I not just remove the EGR valve?

Instead of replacing the EGR valve, which tends to require diagnostic programming afterwards, you may consider either removing it, or fitting a blanking plate. While the consequences of doing this may include slightly higher fuel consumption and a hotter running engine, NOx emissions are certain to skyrocket.

You might not see this as a problem, because NOx emissions are not part of an MOT emissions test. However, it is an offence to remove/disable emissions control systems. In the UK, this issue is dealt with under Section 42 of the Road Traffic Act, referencing the breach of Construction and Use regulations and Regulation 61.5(b) of the Road Vehicles (Construction and Use) Regulations 1986.

For these reasons, your car will fail its MOT test if the tester finds evidence that the EGR valve has been removed, or is not working any longer.

To view these stories or to keep up to date with the latest news from GEM Motoring Assist you can connect with GEM Motoring Assist at:

Twitter: @motoringassist

Facebook: @gemmotoringassist

Instagram: @gem_motoringassist

LinkedIn: @gem-motoring-assist-limited

GEM Motoring Assist is a members’ motoring and road safety organisation in the UK. Our aim is to keep our members on the move… whether that’s through our breakdown recovery service or our motoring and road safety expertise.

Join GEM for simple and straightforward, all-inclusive personal breakdown cover.