Issues with Diesel Particulate Filters are a hot topic with modern diesel car owners however there’s another mechanical gremin in the form of the Exhaust Gas Recirculation Valve or EGR that’s been plaguing drivers for much longer.

What is an EGR Valve?

An EGR or Exhaust Gas Recirculation Valve is a device that recirculates a portion of your exhaust gases back into the combustion process (inlet). This process is primarily aimed at reducing the levels of nitrous oxide (NOx) being emitted through the exhaust system.

NO2 is a harmful air pollutant in its own right, but also reacts in the atmosphere to form ozone (O3) and acid rain. Nasty stuff!

How does an EGR valve work?

EGR valves work by redirecting a proportion of the vehicles exhaust gas back into the intake manifold. In older generation of vehicles the EGR valve was controlled by simple sensors like temperature and vacuum. In modern vehicles they are controlled by the brain or ECU (Electronic Control Unit).

What are the benefits of an EGR valves?

  • Reduced EmissionsThe valve reduces the production of nitrous oxide using recirculated exhaust gases, this has the effect of cooling down the combustion chamber temperature.  The dangerous Nitrous Oxides emissions are formed when engine chamber temperatures rise above 2500 F. By keeping the combustion chamber cool the EGR valve is able to reduce nitrous oxide NOx emissions produced by the vehicle’s engine.

An EGR valve also benefits your vehicle by

  • Reducing the potential of throttling losses on spark ignition engines (i.e. Petrol) at part load
  • Improving engine life through reduced cylinder temperatures (particularly exhaust valve life)


How will I know if my EGR valve is malfunctioning?

As with most modern cars, when the ECU detects an issue it will display either the relevant warning light or the check engine light. If you have access to a ODB ii tool you may well be able to read the fault code the car is reporting. The most common code reported for a faulty or malfunctioning EGR valve is

  • P0401 – Insufficient EGR Flow
  • P0402 – Exhaust Gas Recirculation Flow (EGR) Excessive Detected
  • P0403 – Exhaust Gas Recirculation Circuit Malfunction

If you don’t have access to a ODB ii scanning tool then it may well help you diagnose this and future issues without the need of a mechanic, thus saving you costly diagnostic feels. Both ebay and amazon have a large ranges of ODB ii tools available at very reasonable prices.

If you are reporting one of the codes above then it may also help to seek advice from one of the many forums or owners clubs catering for your model of car to see if someone can confirm what the error code corresponds to.

What are common problems associated with EGR valves?

Even though EGR valves provide vast environmental and air quality benefits, they are also associated with issues which are most commonly experienced by diesel car owners.

  • Increased exhaust particulates
    EGR valves reduce the available oxygen in the cylinder, this in turn increases the production of particulates (fuel which has only partially combusted). This is most commonly experienced by diesel engines traditionally been a problem with diesel engines. These particulates are one of the main reasons diesel engines are now fitted with the diesel particulate filters or DPFs. A faulty EGR valve that is stuck open will increase the amount of particulates produced by the engine, causing your DPF to become blocked quicker than usual. Read more about DPF filters in our diesel particulate filter FAQ page.
  • Detonation
    This is also known as pinging or spark knock. This can occur when your EGR system simply isn’t working, when the EGR valve is disabled or when your exhaust port is clogged with carbon.
  • Misfiring or rough idle
    This happens when your EGR valve fails to close, causing exhaust to leak into your intake manifold.
  • Hard starting
    This may occur when the EGR valve isn’t closing, thus resulting in a vacuum leak into your intake manifold.

How to clean an EGR valve?

Over time EGR valves and malfunction due to a build-up of carbon and other deposits associated with the exhaust gasses passing through them. This can cause the device to be stuck open, closed or even fail completely.

These harmful deposits can be removed using a number of ways

  • Replacing the EGR Valve
    The quickest, simplest and quickest way to unblock an EGR valve is to replace the unit with a new one. Theres no soaking or elbow grease required however unless you are handy with the spanners your local mechanic will charge you for this procedure.
  • Removal and Cleaning of the EGR Valve
    The next best option to replacing the EGR valve is to have it cleaned. This also required the removal of the device however without the added expense of the replacement parts. Usually the valve is submerged in a solution such as carb cleaner and left for a period of time. It can then be fully cleaned using some sturdy brushes and a small application of elbow grease. Just remember not to submerge any electrical connectors if you are leaving it to soak and make sure you replace any gaskets that you have to remove.
  • EGR cleaning Sprays
    If removing the EGR valve is a little beyond your mechanical ability then there are various EGR cleaning sprays available from retailers such as Amazon. These are sprayed directly into the inlet manifold (after the turbo) or directly into the intake system (remove the air filter and spray). They contain an chemicals that dissolve gum, lacquer, tar, carbon and deposits from the valving, allowing it to work correctly.
    These products are designed to clean the entire intake system and the EGR valve and judging by the forum posts and review I have read seem to work very well. Just be careful to follow the directions closely.

  • Fuel additives
    There are a number of fuel additives available that claim to be able to clean an EGR valve without any removal or physical cleaning of the device. We suggest that you steer clear of such products and invest your time and money into either having it cleaned professionally or taking the time to do the job yourself.

Blocked EGR Valve showing huge soot and carbon deposits build up


How do I remove / block an EGR valve?

A whole industry has built up around the removal and blocking of problematic EGR valves. The blocking or complete removal of the valve is still a contested subject. Before you reach for the blanking plate please take the following into consideration.

  • Removing it won’t improve performance
    EGR valves do not open when the throttle is wide open. Removing it will not give you a couple of horses extra for the traffic light GP however a malfunctioning may well reduce your power.
  • Removing it won’t save you fuel
    As above the EGR is designed to reduce combustion chamber temperatures in order to reduce harmful emissions. A side effect of this is that the engine runs more efficiently in the process, saving you fuel and the environment from harmful nitrous oxide (NOx) emissions.

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Is it illegal to remove or disable your EGR valve?

This is a question posted in the comments section of this page and a very good one at that. You can read more about that in our Is it illegal to remove or disable your EGR valve page.

We hope you found this article useful and we’ll be adding to it’s content as time goes by. We’d love to hear about your experiences with your EGR related issues so please feel free to leave a comment below