Toyota EGR valve: understanding exhaust gas recirculation valves

What is an exhaust gas recirculation (EGR) valve?

The EGR valve in your Toyota is fitted within the exhaust system and allows some of the gases produced during the combustion process to be re-burnt within the combustion chamber for a second and more effective time. This occurs when the correct engine operating conditions are met and, in turn, serves to reduce harmful emissions.

What does an EGR valve do?

The process of recirculating precise quantities of exhaust gases back into the combustion chamber has a number of advantages. In petrol engines, it helps to lower combustion temperatures and reduces the chance of spontaneous combustion, also known as knock. This allows the engine control unit (ECU) to dilute the air/fuel mixture and reduce petrol consumption.

In diesel engines, the role of the EGR valve is even more important. Routing exhaust gases back into the combustion chamber also lowers combustion temperatures, but the primary benefit is the reduced formation of nitrous oxide (NOx) particulates. In addition, the reappearance of spent exhaust gases within the combustion chamber enables the engine to neutralise these particulates through secondary burning.

Does the work of the EGR valve relate to the function of the particulate filter in diesel engines?

Yes, but indirectly. The neutralising of NOx soot within the combustion chamber reduces the quantity of this material heading into the diesel particulate filter (DPF) installed further down the exhaust system. This increases the time period between regeneration procedures and the service life of the DPF itself.

Why might an EGR valve fail?

Its location within the direct path of flowing exhaust gases means that soot can accumulate around the EGR valve and block its free movement. It is possible to mitigate this by ensuring the vehicle is regularly driven at sustained speeds above 40mph. Constant use of any vehicle in low-speed, urban environments with frequent stops will accelerate the amount of soot collecting around the EGR valve.

How can I tell if the EGR valve in my car is failing?

A failing EGR valve will affect the performance and economy of your engine, though it is likely that the ECU will notice the issue and alert the driver through a dashboard warning light before any physical symptoms are experienced. These symptoms may include rough idling, hesitance in acceleration and a loss in fuel economy.

What do I need to do if I see the engine check light illuminate?

Return the car to your main dealer to be checked. If the fault code displayed by the diagnostic equipment relates to exhaust gas recirculation, the likelihood is that the valve will need to be either cleaned or replaced. Cleaning is much cheaper than replacement, so it is prudent to react immediately to all warning lights.


  1. Hi there a non Toyota garage has fitted a new EGR valve and air mass sensor to my Toyota Avensis T180 diesel but it is still not working. They claim to have fitted Toyota parts so what other issues can be causing the lack of power?

    1. Hi Jane,

      Impossible for us to say based on this message alone. Please contact your nearest Toyota centre so they can physically inspect the vehicle.


  2. Dear Jane
    i have a land cruiser d4d 120 with 1kdf-tv diesel engine my check engine light comes on and fault error po400
    appears on diagnostic tool i may drive more than one hour with any problem and some times i drive for few minutes with bumpy road then i have check engine on.
    Egr is clean ,valve hold vacuum .no vacuum leak, no sensors wire is broken or failed determined problem appears.
    please help

    1. Hi Jehad,
      Thanks for your comment.
      We would recommend taking your vehicle to a Toyota centre in your region for further assistance as we are only able to advise on UK specification vehicles.

  3. My Rav 4 ran brilliantly until the EGR unit was replaced under recall notice. Since then the car has serious intermittent problems with loss of power, increased fuel consumption and stalling. The local Toyota garage that did the replacement say it’s nothing to do with them and the fault wouldn’t have been caused by the work they did and that it’s just a coincidence. RAC spent 2 hours ‘ fixing’ the problem a couple of weeks ago saying if it happens again they suspect a faulty part has been fitted. It’s happened again! Seriously fed up. Now thinking of trying to drive to the Toyota garage I bought the car from which is 60 miles away as there is no way I trust the local garage to be honest or fix the problem.

  4. Hi
    I have 2008 Toyota parado and I can hear knocking sound in my engine. When this happens the engine check light blinks .
    It’s not a continued knocking sound comes and goes. Engine sound in idle is ok
    What could be the reason.

    1. Hello Ritesh, thanks for your comment.

      We are only able to advise on UK vehicles. Please contact a Toyota Centre in your local area so the team there can take a look at your Prado in person.


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