What Is an EGR Valve?
Ellie Dyer-Brown, 8 months ago
5 min read
- Exhaust
FixMyCar explains what an EGR valve is, what it does, and how to stop it from failing.
EGR stands for exhaust gas recirculation, a process virtually all modern cars use to reduce harmful emissions. One of the most important components in this process is the EGR valve. If you have questions about how it works and why it can go wrong, this guide is for you.
Contents
Where is the EGR valve located?
Symptoms of a failing EGR valve
What is an EGR valve?
The EGR valve is a vital part of the exhaust gas recirculation system that determines the flow of exhaust gases. It connects the exhaust manifold to the inlet manifold and is controlled by either a built-in electric step motor or a vacuum.
What does an EGR valve do?
Put simply, the EGR valve's purpose is to open and close, altering the flow of exhaust gases into the combustion chamber.
Reducing NOx
Nitrogen oxide or NOx is a harmful by-product of the combustion process, which can cause respiratory issues and lung disease. The exhaust gas recirculation system was designed to minimise these emissions by returning a small amount of exhaust gas into the combustion chamber (through the inlet manifold), thereby reducing its temperature and the amount of NOx emitted. The EGR valve is the main part of this system.
How does an EGR valve work?
Before reading about how the valve works, you need to know the link between temperature and emissions: the higher the combustion temperature in an engine, the more NOx it produces.
When the EGR valve opens, it allows some exhaust gas to flow back into the combustion chamber, where it combines with fresh air. This increases the combustion mixture’s water vapour content and lowers the amount of oxygen, which has a cooling effect, lowering the peak combustion temperature.
After you start your car, it takes a while for the engine to reach its optimal operating temperature; once this happens and you increase your speed, the EGR valve starts working, gradually regulating the flow of exhaust gases.
Although the valve has two main positions - open and closed - it can be partially opened depending on the vehicle's speed. It tends to be more open at low speeds because less oxygen is required for the combustion process.
Types of EGR valve
There are a few different types of EGR valve to be aware of.
Petrol EGR - cylinder depression creates a vacuum, which draws exhaust gases in; the opening and closing of the valve controls the flow.
High-pressure diesel EGR - diverts the high-flow sooty exhaust gas before it reaches the diesel particulate filter (DPF). The soot can combine with oil vapour, creating sludge. The gas is then passed back into the inlet manifold. A secondary valve creates a vacuum in the inlet manifold.
Low-pressure diesel EGR - diverts exhaust gas after it has passed through the DPF.
Digital EGR - uses a solenoid or stepper motor and often a feedback sensor. The valve receives a pulse width modulated signal from the ECU to control the exhaust gas flow.
Vacuum-operated EGR - uses a vacuum-controlled diaphragm to open and close the valve.
Where is the EGR valve located?
Most EGR valves can be found on the driver’s side of the engine (either at the rear or on top), between the inlet and exhaust manifold. It may be hidden under another component, making it difficult to access.
Find out more about how car engines work in this guide.
Why do EGR valves fail?
EGR valves often work under high pressure - like any component, they can fail due to normal wear and tear. However, the most common cause of EGR failure is carbon deposits.
As exhaust gases pass through the valve and the passages of the inlet system, carbon deposits get left behind - these are a by-product of incomplete combustion. If they build up, they can block the passages and cause the EGR valve to get stuck open or closed.
The EGR & DPF
The diesel particulate filter and EGR valve are closely linked. If the valve gets stuck open, it allows more exhaust gas to pass through the system, accelerating the accumulation of soot in the DPF. That’s why both components often fail together.
This guide discusses how to avoid DPF problems.
Common EGR valve fault codes
You can use a diagnostic tool to find out what's wrong with your EGR valve. When you plug the tool into your car's OBD port, it will display a fault code providing more information about the issue. Below are some common codes and what they mean.
P1406: EGR system pintle position error
P1405: EGR solenoid high
P1404: EGR system – closed valve pintle error
P1403: EGR solenoid low
P0408: EGR sensor B circuit high
P0407: EGR sensor B circuit low
P0406: EGR sensor A circuit high
P0405: EGR sensor A circuit low
P0404: EGR circuit range/performance
P0403: EGR circuit malfunction
P0402: EGR excessive flow detected
P0401: EGR insufficient flow detected
P0400: EGR flow malfunction
Symptoms of a failing EGR valve
EGR valve failure is often accompanied by:
Poor engine performance - a lack of power can result when the valve is stuck open or closed.
Increased fuel consumption - this is usually a sign that the valve is stuck open.
Rough idling - your car may shake when idling due to the valve being stuck open.
Engine management light - this dashboard warning light will stay on when your valve is stuck open or closed.
The smell of fuel - a strong smell of fuel often happens when the valve is stuck open because, at low revs, not all of the fuel burns, leading to increased hydrocarbon gas emissions from the exhaust.
Knocking engine - knocking noises from the engine can be caused by a valve that is stuck closed. It happens because fuel ignites early at low RPMs when it encounters heat.
Unfortunately, most of these symptoms can be caused by a range of other problems, which makes it difficult to diagnose a faulty EGR valve without further investigation. It’s important to get your car checked by a mechanic as soon as possible to avoid damaging your engine.
How to prevent EGR valve failure
There are a few proactive steps you can take to prevent EGR problems.
Keep up with regular maintenance
You should aim to keep your engine running as clean as possible. Replacing your fuel filter and engine oil at the correct intervals is crucial because it helps prevent the build-up of dirt and carbon deposits, which can cause the valve to stick.
Booking a full service each year is a great way to stay on top of your car’s maintenance without having to schedule multiple garage appointments. Between services, check your oil regularly (if it’s dark or sludgy, it needs replacing).
Find out what’s included in a full service here.
Use a fuel additive
You could also use a cleaning fuel additive as a preventative measure - this is more important if you have a diesel car, but petrol additives are also available. All you have to do is pour the contents into your fuel tank, and as you drive, it cleans the system.
Drive on the motorway
Taking your car for a blast on the motorway every couple of weeks is another way to prevent carbon deposits because it allows your engine to get hot enough to burn them off.
Use premium fuel
Opting for premium fuel when you fill up at the pump could help protect the EGR valve. Premium diesel often contains additives to prevent engine fouling and remove soot deposits.
How to clean an EGR valve without removing it
The best way to clean your EGR valve without removing it is to use an EGR valve cleaning solution, which you spray into the engine while it is running at around 2,000 RPMs. The most popular EGR valve cleaner is by Wynns - you can buy different versions depending on whether you have a petrol or diesel car. You must follow the instructions carefully when using it.
Using an at-home EGR cleaner requires some mechanical knowledge to access the correct part of the engine. If you don’t feel confident doing this, you could book a professional EGR valve clean instead. You should also choose this option if your valve is entirely, rather than partially, stuck.
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