What Causes EGR Valve Failure? (Answered!)


Your car’s EGR valve is an important part of the emissions control system. It helps to reduce NOx emissions by recirculating exhaust gases back into the engine. EGR valve failure is a common issue that can occur in any vehicle, but what causes it?

In this comprehensive guide, we will discuss the causes of EGR valve failure and how to prevent it from happening. We will also cover the symptoms of a failed EGR valve and what to do if it fails. So, if you are concerned about the health of your EGR valve or want to learn more about how to keep it functioning properly, keep reading!

What Causes EGR Valve Failure?

What Causes EGR Valve Failure

What causes EGR valve failure? Carbon and soot build-up from the exhaust gases can cause the EGR valve to fail. When this happens, the exhaust gases may not be recirculated back into the engine in the amount requested by the engine computer, resulting in higher temperature in the combustion chamber and more nitrogen oxide being released into the atmosphere.

Exhaust gas recirculation was once only a gasoline engine concern. However, later on, diesel engines started using this method to control combustion chamber temperature and the production of nitrogen oxides.

EGR valves are only active or open during 1000 RPMs and 2000 RPMs. The reason why the EGR valve is active only during low engine speed is that by activating and recirculating exhaust gases, it reduces the engine power. This is because hot air is less dense, therefore, less air equals less engine power.

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What this means is that if you are driving your vehicle mainly in heavy traffic where you can’t get above 2000 RPMs, your EGR valve will constantly be open. This leads to premature EGR valve failure because it will be in constant contact with carbon dioxide which tends to build up on the walls of the EGR valve and cause it to fail.

The carbon dioxide concentration in the exhaust gases from a typical passenger car is around 14% by volume. For a diesel engine, it can be as high as 22%. The rest is made up of nitrogen (around 78% for a petrol engine and around 75% for a diesel engine), oxygen, and water vapor.

The EGR valve is constantly in contact with exhaust gases and carbon dioxide. Over time, the EGR valve gets blocked by carbon buildup which causes the valve to fail. When this happens, the EGR valve is not able to recirculate the exhaust gases into the combustion chamber. This will lead to increased temperature within the combustion chamber and more nitrogen oxide being released into the atmosphere.

Can a Bad EGR Valve Cause Engine Damage?

What Causes EGR Valve Failure

Can a bad EGR valve cause engine damage? Yes, a bad EGR valve can cause engine damage. A bad EGR valve stuck in an open position can restrict the engine from fresh air and only feed it carbon-rich exhaust gases which can affect the air-to-fuel ratio, or if stuck in a closed position, it can flood the engine with fresh air and increase the combustion temperature. Either way, the normal operation of the engine will be affected and the engine could misfire, share at idle, or overheat.

EGR is an emission control device that is used in engines to reduce the amount of nitrogen oxide released into the atmosphere and reduce the combustion temperature by redirecting a portion of the exhaust gases into the engine inlet.

When the EGR valve fails, i.e gets stuck in an open or closed position, your vehicle will exhibit certain changes.

When the EGR valve gets stuck in an open position, more carbon will be drawn into the engine which causes the engine to basically starve for fresh air. This causes the air intake sensors to miscalculate false air intake and decrease the fuel injection even further. With the air to fuel mix ratio thrown off balance due to the EGR valve stuck open, your engine will run rough, vibrate, and shake which can cause engine damage.

When the EGR valve is stuck in a closed position, the opposite happens. In this case, more fresh air goes into the engine which increases the combustion temperature. The increase of the temperature in the combustion chamber can make a knocking sound and often results in engine overheating.

How Long Should an EGR Valve Last?

How long should an EGR valve last? An EGR valve is designed to last for up to 10 years or 50,000 miles. However, the durability of an EGR valve is greatly affected by the way you drive your vehicle. This is mainly because the EGR valve is usually activated between 1000 RPMs and 2000 RPMs. If you drive your vehicle in heavy traffic, the EGR valve will be activated most of the time, causing it to fail sooner.

The EGR valve has a mission to reduce the amount of harmful toxins being released into the atmosphere and to reduce the temperature of the combustion chamber. This is being accomplished by allowing some of the exhaust gases to be redirected back through the engine’s intake to be burned off again in the combustion process.

When the EGR valve opens, it redirects hot exhaust gases back into the combustion chamber. This is done only on lower speeds because hot air is less dense than fresh air and results in less engine power. This means that if you drive your vehicle in lower speeds with 1000 to 2000 RPMs, the EGR valve will constantly be activated. The more the EGR valve is activated, the less time it will last.

You can increase the longevity of the EGR valve by driving mainly at highways instead of heavy city traffic. Another thing that you can do to increase the durability of the EGR valve is to clean it occasionally. You can either clean the EGR valve without removing it, or you can remove the EGR valve, inspect it, and clean it.

If you decide to go with the second method and actually remove the EGR valve, make sure to inspect it. Check the condition of the EGR valve. If it should be changed, make sure to get a high-quality EGR valve from a known manufacturer. There are some high-quality EGR valves on amazon.com.

Will a Bad EGR Valve Throw a Code?

Will a bad EGR valve throw a code? Yes. A bad EGR valve can throw a couple of codes including P0401 if the EGR valve is not flowing enough recirculated exhaust gases when ordered by the ECM, or a P0402 code if the EGR valve is flowing too much recirculated exhaust gases into the intake manifold.

The purpose of the EGR valve is to open up and recirculate part of the exhaust gases back into the intake manifold. These exhaust gases help reduce the temperature of combustion. NOX is formed in high temperatures so by reducing the temperature of combustion, it reduces the NOX formation.

When it comes to a symptoms of a bad EGR valve, it can go two different ways; Stuck open EGR valve, or stuck closed EGR valve. In both cases, a bad EGR valve will throw a check engine light on the dashboard, and an error code if you scan your vehicle with OBD scanner.

In fact, a bad EGR valve can throw total of 10 codes:

OBD-II Error CodeMeaning
P0400EGR valve not flowing recirculated exhaust gases when ordered by the ECM
P0401EGR valve not flowing recirculated exhaust gases when ordered by the ECM
P0402EGR valve flowing too much recirculated exhaust gases into the intake manifold
P0403EGR circuit has malfunctioned
P0404EGR valve or sensor is out of specification range
P0405EGR sensor is operating below specification range
P0406EGR sensor A runs at high circuit voltage
P0407The EGR system is facing a voltage problem
P0408PCM has detected an issue with the EGR system
P0409The EGR sensor A circuit has malfunctioned

Can You Run a Car Without an EGR Valve?

Can you run a car without an EGR valve? From a mechanical point of view, yes, you can run a car without an EGR valve. The strength of the engine would be significantly reduced, the vehicle could shake at idle, misfire, or not start at all. However, looking from an legal point of view, driving a vehicle without an EGR valve is considered illegal in most states.

EGR valves are anti-poluttion devices that are designed to recirculated some of the exhaust gases back into the combustion chamber when ordered by the vehicle computer.

Before EGR valves were invented, older vehicles had catalyc converters that used to burn pollutants. However, they got too hot because while burning the pollutants, sometimes they burn the unburned hydrocarbons which created extra heat. So, the engineers got together and created the EGR valve. Now, the EGR valve recirculates inert gas with very little oxygen back into the combustion chamber that burns at lower temperatures.

Driving with a faulty EGR valve or without an EGR valve is possible. You would definitely feel a difference while driving. Many car owners report that they car started to shake at idle, they saw a check engine light on their dashboard, excessive vibrations, or they couldn’t start their vehicles in the first place.

But, let’s say you do start your vehicle without an EGR valve. Because you don’t have an EGR valve, there is no anti-pollutant device on your vehicle. If the EGR valve is not recirculating exhaust gases and lowering the temperature, you are now polluting the atmosphere with NOX. This is considered illegal in many states, and will definitely get you to fail emissions test.

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Hi there. I am a certified Automotive Service Excellence (ASE) mechanic since 2018 and a car detailer for 10 years.

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