What are the Signs of a Bad EGR Valve and how to fix it?

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What are the signs of a bad EGR valve, and how to find out when should you go for engine maintenance? The information in this article will answer your question.

The EGR valve is an essential part of the engine that returns a portion of the exhaust gas to the air intake. As a result, it can help to reduce the NOx pollutant concentration.

Bad Egr Valve

A typical bad EGR valve

EGR valve will help reduce pressure on the engine and help the engine operate smoothly. If the EGR valve gets trouble, you will probably encounter stalling or difficulty starting the car.

But, when you are in trouble, how can you know if it is an EGR valve problem or not? We want to say that it is essential to find out What are the Signs of a Bad EGR Valve because you can only solve the problem without destroying your car’s engine once you know its origins.

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What is the Mission of EGR – Exhaust Gas Recirculation?

The exhaust gas recirculation valve or EGR valve is responsible for allowing the exhaust gas from the engine to return to the intake manifold and re-enter the combustion chamber. A Vacuum or an ECU will control this valve.

After entering the combustion chamber, the exhaust gas will mix with new air and reduce the temperature of the combustion process. Thereby, it can reduce the amount of NOx generated. The EGR valve will close if the engine does not work. And once you drive your car at high speed, the valve will open gradually depending on the control signal of the ECU.

Bad Egr Valve

EGR valve plays an important role in the engine

Types of EGR Valves

Both petrol and diesel engines consist of exhaust gas recirculation. On older models, you will see the lid is round, thin, about three inches in diameter, and controlled by a vacuum tube. This vacuum tube is connected to throttle or carburetor.

The EGR valve body consists of a vacuum diaphragm, springs, and pistons. And there are some differences among the older and the brand-new car:

  • Usually, cars are equipped with an electronic EGR valve with an EGR valve position sensor and solenoid connected to the computer system. It will make the valve control more accurate.
  • For newer cars, producers equipped it with a VVT-I variable valve timing system, so there will be no exhaust circulation system.

Process of Exhausting the Engine Gas

The air entering the engine contains 80% nitrogen and 20% oxygen and a small number of other components. When the air combines with fuel and burn, the temperature can reach 1370 degrees C.

At this temperature, nitrogen gas can be burned and create NOx gas, which will pollute the environment and severely affecting human health. However, when exhaust gas is fed into the combustion chamber, the combustion process will limit and reduce the temperature of the combustion chamber. And as a result, it can limit the formation of NOx, too.

Bad Egr Valve

A strong EGR valve

What are the Signs of a Bad EGR Valve?

Now let’s come to the essential part of this article: what are the signs of a bad EGR valve? One common sign of a failed EGR valve is OBD II code P0401, this code indicates that the EGR valve isn’t letting enough exhaust through.

There are two main types of a bad EGR valve: the 1) valve is stuck and closed and 2) lid is blocked and open.

1. Valve Stuck and Open

If the valve is blocked, the exhaust will continuously enter the combustion chamber and will cause the following bad EGR valve symptoms:

  • The moto shakes when the engine is started (when the engine is still cold) and when the engine speed is low.
  • Stalling while you are on the road or dead machine while you are driving in moderation
  • The exhaust gas smells like fuel because of the increased hydrocarbon content in the system
  • When the engine is running at low speed, the low combustion chamber temperature will prevent the fuel from being burned so that the exhaust gas will have a smell of fuel
  • The engine error indicator with the light on the dashboard
Bad Egr Valve

Stalling and dead engine are the two common signs of a bad EGR

2. Valve Gets Stuck and Close

If the EGR valve is stuck and closed, it will prevent exhaust gas from entering the engine and cause the following symptoms:

  • When you drive at low speed (higher than moderate pace), you will hear a sound of knocking inside the engine. This knock comes from the internal detonation of the engine due to the combustion chamber temperature is too high.
  • A big bang! The detonation will cause internal damage to the engine and cause loud explosions.
  • The motor error indicator lights up.

Is There Anything that You Can Do?

Well, after finding out the common symptoms of a bad EGR valve, we think your next question is, “what should you do” and “is there anything that you can do by yourself to fix it?”

We think what you can do is check the problems carefully because the EGR valve is not the only factor that leads to an increase in the number of hydrocarbons. Besides, EGR valve, there are so many other factors that result in the same situation, for example, leaking injector, wrong ignition timing, compression ratio, damaged oxygen sensor.

Typically, the increase of NOx in the exhaust gas is due to leakage of the vacuum, clogged injectors, low fuel pressure, or leaking of the lid. If your car’s engine shakes when running in moderation, it could be a consequence of a vacuum leak or damage to the ignition system.

Thus, the symptoms are very diverse and caused by various causes. So you need to check the EGR valve and other parts to identify the problem. For cars equipped with electronic EGR valves, you can use a diagnostic machine to identify the error code and see if it is an EGR valve problem or not.

Finally, to make sure that your engine is healthy if you face any of the above signs, you should bring your car to the garage to get professional rechecked.


As a driver, you will always have to face an unexpected situation, and not all of them are comfortable. When mentioning to the engine, we want to emphasize that this is an essential part of the car. For more information, you will always have to pay more to repair the engine than repair other parts of the vehicle.

And the EGR will help to keep your car engine strong and healthy. So you must have some knowledge of “what are the Signs of a Bad EGR Valve and what you can do.

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