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What is the EGR valve and what does it do?

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Updated 11 Oct 2019Joel Ilton
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When was the last time you thought about what’s happening under the bonnet of your car?

A lot of us take for granted the fact we can just jump in, hit the key and be on our way, but we never really give a thought to the complex process happening just in front of us.

The well-timed ignition of the air and fuel mixture that provides the drive to power us forward to our destination is a wonder in itself but, unfortunately, there are side effects to this process - mainly, harmful exhaust emissions.

Thankfully, manufacturers have been trying to combat these harmful emissions, implementing many emissions control devices to reduce the impact on the environment.

One of these devices is known as the Exhaust Gas Recirculation valve - or EGR for short.

The EGR is usually located on the inlet manifold of the engine, although sometimes it can be located lower down near the exhaust manifold.

It operates by recirculating exhaust gas back into the engine through the intake.

This gas is cooler than the combustion temperature inside the cylinder, which reduces the production of oxides of nitrogen.

This is one of the most harmful types of gas for our environment and is produced in high combustion temperatures, such as in diesel engines.

The downside of reducing these oxides of nitrogen by utilising an EGR valve is the increased level of carbon particulates produced.

This is where another emissions control device comes in - the diesel particulate filter (DPF)

The DPF works in harmony with the EGR valve to reduce both harmful oxides of nitrogen and carbon particles from entering the atmosphere.

As the diesel engine is the biggest offender when it comes to these emissions, their petrol-powered brethren are usually only fitted with an EGR valve.

As emissions targets became stricter across the world, manufacturers had to come up with more efficient EGR operation to further reduce their impact.

This is where the EGR cooler comes into play. The EGR cooler utilises the cooling system of the engine to further cool the exhaust gasses before they enter back into the air intake, thus bringing down combustion temperatures even further, but increasing the workload of the DPF.

If any of these systems become clogged with excess carbon build up, drivability may be compromised and more harmful emissions will be released into the atmosphere.

It is possible to try cleaning the EGR valve, and there are dedicated cleaning products available in the aftermarket.

Unfortunately, if the cleaning is not successful, replacement may be the only option.

This can be a costly repair, so it is worth thinking about the many systems in your vehicle, and following the manufacturer's recommendations for servicing and maintenance to ensure smooth and stress free motoring every time you turn the key.

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Written ByJoel Ilton

Finding a passion for cars from a young age, Joel carried out work experience as a mechanic whilst at school before starting an apprenticeship after finishing year 12.

After almost 10 years on the tools and in customer service, he moved into the IT realm as a Data Analyst and In-House mechanic at AutoGuru.