Exhaust Gas Recirculation valve

Exhaust Gas Recirculation Valve: What It Is And How It Works

These days, cars use a wide array of systems and components to try to reduce their footprint on the environment as much as possible. Surprisingly, and contrary to the common opinion, this is nothing new. Yes, newer anti-emission systems are a lot more efficient than they were before but some of them have been used for a long time. Thanks to the evolution of technology, some components were significantly improved with time. One of these systems is the exhaust gas recirculation system and specifically the EGR valve. While it plays an important role in reducing your car’s toxic emissions, a faulty ERG valve may significantly reduce your car’s performance. Luckily, we’ve created this guide to help you understand what an EGR valve does, how different models work and what are their respective pros and cons.

What Does EGR Stands For?

In simple terms, EGR stands for Exhaust Gas Recirculation. The EGR valve is part of your vehicle’s emission system along with other components. The canister purge valve, for example, is also part of the same system but acting on a different one. The EGR system is used to recirculate a portion of the burnt exhaust gases back into the intake air stream with the aim to cool down the interior of the combustion chambers. As NOx gases are mostly created when nitrogen and oxygen are subjected to high temperatures, doing so will significantly reduce the emission of NOx in the atmosphere.

Furthermore, cooling down the combustion chambers also reduce the loss of heat to the surrounding areas. This will allow more heat to be transformed into more kinetic energy during the next cycle, leading to more power.

Vacuum hose drawing

How Does an EGR Valve Work?

At low temperatures and when a vehicle is not under a load, very little NOx is produced. Since little NOx is being created, the EGR valve is not needed. There are different valve models operating in different ways but they can all be opened or closed on demand.

Which Cars Use Exhaust Gas Recirculation Valves?

EGR valves have been common on most gasoline and diesel engines since the 1970s. Most cars on the road these days have one. However, EGR valves work for diesel and gas engines differently.

However, some of today’s most modern engines no longer require an EGR valve. Variable Valve Technology allows adjusting the timing of the exhaust valves, producing to the same effect of an EGR valve. Advances in VVT technology may make EGR valves obsolete soon.

For example, a new engine developed by supercar builder Koenigsegg uses individual electric solenoids to activate each valve rather than a mechanical camshaft. If this technology takes off, the EGR valve function will automatically be incorporated into the function of the engine.

Types of EGR Valves

There are at least six types of EGR valves in use today. Each functions differently but accomplishes the same purpose. Some of the most common types are explained below. Each has benefits and limitations.

Vacuum-operated EGR Valve

Vacuum-operated exhaust gas recirculation valve
This is a common vacuum-operated EGR valve. While this type of valve does work fine, it is definitely not as efficient as newer designs.

The original exhaust gas recirculation valve is still in use today on many types of cars and trucks. This type of EGR valve relies on engine vacuum coming typically from the intake manifold to open and close a valve to allow the recirculation of exhaust gases. To make it simple, when the driver steps on the gas pedal and put the engine under load, the sudden drop in pressure inside the intake manifold will pull on a small diaphragm inside the valve. Doing so will make the valve open up and allow the gases to go through.

While functional, this type of EGR valve is the least responsive to changes in the engine operating condition.

Electric EGR Valve

Electric exhaust gas recirculation valve
With the advances in electronics, engineers have been able to incorporate electric solenoids instead of the diaphragm to open up the valve.

An electric EGR valve is controlled directly by the powertrain control module. This common type of EGR valve reduces emissions significantly more and gives better performance improvements.

At least three main types of electric EGR valves are in use today:

  • Linear EGR valves – operated by the PCM according to the feedback the computer receives from the Throttle Position Sensor, Mass Air Flow Sensor, Engine Temperature Control, and RPM;
  • Dual EGR valves – operated by a PCM-controlled solenoid and a vacuum-operated valve;
  • Advanced EGR valves – controlled via the PCM and also a vacuum-operated valve with a pressure differential switch that allows even greater efficiency.

Electric EGR with Cooler

Electric water-cooled exhaust gas recirculation valve
A cooler charge of exhaust gases can help to improve engine efficiency even more. Many diesel engines use EGR valves that incorporate a cooler and a particulate filter.

It is commonly known that a cooler, denser charge of air leads to more power and even fewer emissions. A downside of most exhaust gas recirculation systems is the re-introduction of hot exhaust gases into the already hot combustion chamber. An electric EGR with a cooler helps to offset the exhaust heat to lower temperatures and increase efficiency. These types of EGR valves can significantly reduce emissions, but can also cause other problems particularly with diesel engines that tend to recirculate soot with the exhaust gases.

DC Motor EGR valve with Hall Sensor Response

These are common in diesel engine applications that require a quick-opening valve with increased opening pressures.

EGR Operation on a Common Rail System

Used in both diesel and petrol applications, this type of EGR valve creates a greater pressure difference between the exhaust and intake pulses.

Throttled Turbo EGR Valve

A new idea under experimentation uses a throttle valve within a turbocharger to decrease intake pressure, thereby increasing EGR effectiveness within the cylinder. This technology is under development for modern, clean diesel technology.

EGR Valve electrical system diagram

EGR Valves Reduce Emissions and Increase Performance

Excessive smog levels encouraged regulators to pressure engineers to create devices that lowered emissions. Early examples of EGR valves did reduce emissions but also decreased fuel efficiency and reduced performance. These shortcomings partially or totally offset the effects of an exhaust gas recirculation valve.

As engineers became more knowledgeable about the effects of exhaust gas on the combustion cycle, they came to understand the positive and negative effects. Vacuum-operated EGR valves function well to reduce NOx, but can also introduce hot, dirty air into the combustion chamber that reduces the amount of fresh oxygen available. This can reduce the efficiency of the engine and can lead to excessive unburnt fuel in the exhaust stream.

Development of Cooled EGR Valves

Reducing temperatures required that engineers design EGR valves that cool the air. Engineers working on diesel engines developed some of the earliest cooled EGR valves. The cooler air charge tended to cause the accumulation of soot. Eventually, soot creates significant problems in your intake chambers. Soot forms in the moisture, and builds up in your combustion chambers.

As cooled EGR valves came onto the market, most manufacturers also began introducing diesel particulate filters. These filters can extract a majority of the soot from the recirculating exhaust, thereby preventing the effects of too much soot. Owners of diesel-powered cars and trucks need to replace their diesel particulate filter periodically.

electric EGR valve

More Power from better EGR Valves

The computer-controlled engines we have available today take advantage of EGR valve performance. Exhaust gas recirculation valves help by reducing emissions and increasing performance. A cooler, denser charge of air has a better combustion pattern, leading to a significant increase in fuel efficiency and power.

Last Words

An exhaust gas recirculation valve is not a stand-alone device anymore. Most exhaust gas recirculation valves in use today require input from the PC’M to operate correctly. Inputs are variable and require that components like your Mass Air Flow Sensor and O2 Sensors are functioning correctly. Problems with these sensors can make PCM-controlled EGR valves work less efficiently.  Bad sensors can cause long-term problems, including the degradation of catalytic converters.

To prevent expensive repairs, you must make sure every component of your emissions system is functioning at its peak. Today’s systems are all integrated, and a bad component in one system may cause issues with other components. We’ll never say it enough. A properly maintained vehicle is your best bet to have the most bang for your bucks out of it.


About Derek F

Derek grew up in Southern California and started working on cars when he was a child. He learned from his father and grandfather how to make basic repairs and maintain cars correctly. Derek rebuilt his first engine at 15 years-old, beginning an automotive career that took him to many interesting jobs. Derek has worked as an automotive detailer, managed parts warehouses and auto parts stores, and worked as a mechanic for several years doing brake and suspension work. While pursuing a bachelor’s degree in government journalism, Derek worked for an auto museum where he started to write about cars. Today, Derek uses his expertise gained from many years of practical experience to help educate DIYers and share interesting knowledge about various types of automotive repair and service. Writing about cars helps fund his numerous classic car restoration and customization projects.

Leave a Reply

Your email address will not be published. Required fields are marked *