Inside Your Car 12 December 2022

What is an EGR valve?

It’s never a good sign when you’re out on the road and you notice plumes of black smoke coming from your car’s exhaust pipe… but if you do, you may have a faulty EGR valve.

The EGR valve, or Exhaust Gas Recirculation valve, is a device installed in both petrol and diesel vehicles to control harmful emissions. It was introduced as a way to curb pollution, and is a feature of many modern vehicles.

Let’s take a look at what an EGR valve does, and how you can ensure that it’s functioning as it should.

What does an EGR valve do?

The goal of an EGR valve is to reduce the nitrogen oxide (NOx) that your engine produces during combustion, which is what causes the smog that comes out of the exhaust pipe.

It does this by recirculating some of your vehicle’s exhaust gas to be reused in the combustion process. This lowers the temperature of combustion to prevent NOx forming in the first place, resulting in a cleaner system overall.

The EGR valve operates while your vehicle is running, but is disabled during idling and full acceleration, as it would impact your vehicle’s performance at these times, causing it to stall or lose power.

This is why it’s so important to ensure correct EGR valve function, as a poorly functioning valve would mean higher emissions, or loss of performance if the valve gets stuck open or closed.

Where is the EGR valve located?

The location of the EGR valve can be different depending on the make and model of your vehicle and its engine setup, so it’s not always easy to find. Generally, it will be located near the top of the cylinders, connected to the intake manifold, as this is where it recirculates the exhaust – and sometimes it’s found on the exhaust side of the engine assembly, with plumbing back to the intake.

Signs of a blocked EGR

Over time, the EGR can become blocked due to a buildup of carbon deposits from the exhaust mixed with oil, which looks like a sticky tar-like substance. This happens in both petrol and diesel engines, although diesel engines tend to be more prone to it.

If the EGR is blocked, it can get stuck open or closed, resulting in too much exhaust getting into the cylinders at the appropriate times, or not enough. The EGR valve can also fail due to a tear in the vacuum seal if your vehicle uses this kind of system.

Here are a few common problems that point to a failing or blocked EGR valve:

Check Engine light is on: This can obviously happen for many other reasons, but in this case the engine computer has detected the valve is malfunctioning.
Black exhaust smoke/fuel smell in and around the vehicle: This is a sign that unburnt fuel is exiting through the exhaust pipe.
Decreased engine power/stalling at low speeds: This happens when too much exhaust gas is flowing into the cylinders at the wrong time.
Rough idle: When your engine is cold, a rough idle is caused by the EGR valve getting stuck open and causing the temperature in the cylinder to get too low. If it’s idling rough after it’s warmed up, it’s a symptom of an EGR valve that’s stuck closed – however you’d expect to see an engine light on with these symptoms.
Engine knocking noises: This is due to increased temperatures in the cylinder, causing fuel to ignite when it shouldn’t. Current engine computers will detect this early and throw and engine light.
Reduced fuel economy: If the EGR is faulty, it can mean lower temperatures in the engine, meaning that the fuel is not being ignited efficiently.
Failed emissions test: As the EGR is an emission reduction device, if it isn’t working properly your vehicle won’t pass an emissions test and will throw an engine light.

A faulty EGR valve can cause lots of different issues that can have a huge impact on your vehicle’s performance, so it’s good to be aware of them.

Understanding different EGR systems

If you drive an older car, it probably has a pneumatic vacuum-regulated EGR valve, which uses a vacuum to control when the valve opens and shuts. This has just two states—open and closed.

Modern cars, on the other hand, use an electronically controlled EGR valve, where the valve receives input from the car’s Engine Control Unit (ECU). These are more sophisticated and use sensors to gauge how much exhaust to let in and when, creating greater emissions reduction and efficiency.

If your EGR valve isn’t working, mycar can help

If you notice that your car isn’t running properly and you suspect a faulty or blocked EGR valve, bring it into mycar and we’ll help you pinpoint the problem. Our experienced mechanics can inspect the valve and let you know if it just needs a clean or if you need a whole new replacement valve.

So give us a call today and one of our friendly team members will arrange an appointment with a mycar specialist near you.