When Does EGR Valve Open for Diesel? (Purpose + Solution) | OneStopWheel (2023)

The EGR (Exhaust Gas Recirculation) valve is a critical component in diesel engines, responsible for reducing emissions and improving fuel efficiency.

With the increasing pressure to lower emissions and comply with stricter regulations, understanding the role of the EGR valve, its functionality, and troubleshooting techniques is essential for diesel engine maintenance.

In this comprehensive guide, we will dive deep into the diesel EGR valve, discussing when it opens, how it works, and how to troubleshoot problems associated with it.

Table of Contents

The Purpose of the Diesel EGR Valve

The primary function of the EGR valve in diesel engines is to lower exhaust emissions, specifically nitrogen oxides (NOx). By recirculating a portion of the exhaust gases back into the combustion chamber, the EGR valve reduces the amount of oxygen available for combustion, leading to a lower combustion temperature.

Lower combustion temperatures result in decreased NOx emissions, making the EGR valve an essential component for meeting emission standards.

(Video) Most Common Symptoms Of Bad EGR Valve | Signs of failing EGR

In addition, the EGR valve plays a role in improving fuel efficiency and engine performance. By controlling the amount of exhaust gas recirculated into the combustion chamber, the EGR system helps maintain the optimal air-fuel mixture for efficient combustion, reducing fuel consumption and improving overall engine performance.

When Does the Diesel EGR Valve Open?

The EGR valve operates in a dynamic manner, adjusting its position based on various factors such as engine load, speed, and temperature. It primarily functions in two settings: open and closed. However, the valve can vary between these two positions based on the engine’s requirements.

The EGR valve opens for diesel during idle and low-speed operations. While the engine requires less power, and thus, less oxygen for combustion, the EGR valve gradually opens, potentially reaching up to 90% open at idle.

By reintroducing exhaust gases into the combustion chamber, the valve reduces the oxygen level, leading to a slower burn and lower combustion temperatures.

On the other hand, when the engine demands more power, such as during full acceleration or heavy load operations, the EGR valve closes to ensure maximum oxygen intake for combustion. This results in increased power and torque output.

In summary, the EGR valve continuously adjusts its position based on the engine’s needs, maintaining optimal combustion conditions for improved performance and reduced emissions.

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Types of Diesel EGR Valves

There are several types of EGR valves used in diesel engines, with the main distinction being between vacuum-operated and electronically-controlled valves. Let’s explore the primary types of diesel EGR valves:

Diesel High-Pressure EGR Valves

In high-pressure EGR systems, the exhaust gas is diverted before it enters the diesel particulate filter (DPF), where it carries high soot concentrations. The gas is then passed back to the intake manifold, either through a pipe or internal drillings in the cylinder head.

A secondary valve is also used to create a vacuum in the intake manifold, as diesel engines do not naturally produce a vacuum.

Diesel Low-Pressure EGR Valves

Low-pressure EGR systems divert exhaust gas after it has passed through the DPF, resulting in a lower flow but cleaner gas, free of soot particles. The gas is then returned to the intake manifold via a pipe.

Gasoline EGR Valves

Gasoline EGR valves operate similarly to high-pressure diesel EGR valves. The vacuum created by cylinder depression draws the exhaust gases in, and the flow is regulated by the opening and closing of the EGR valve.

Vacuum-Operated EGR Valves

Vacuum-operated EGR valves rely on a vacuum solenoid to control the valve’s diaphragm, opening and closing the valve. Some of these valves also include a feedback sensor to inform the engine control unit (ECU) of the valve’s position.

Digital EGR Valves

Digital EGR valves feature a solenoid or stepper motor and often include a feedback sensor. These valves receive a pulse-width modulated signal from the ECU to regulate exhaust gas flow accurately.

Causes of Diesel EGR Valve Failure

EGR valves are exposed to harsh operating conditions and are prone to wear and tear. The most common cause of EGR valve failure is the buildup of carbon particles from the exhaust gases along the EGR and intake system passages.

(Video) Exhaust gas recirculation (EGR) made easy

Over time, this buildup can clog tubes, exhaust gas channels, and eventually the valve’s plunger mechanism, causing it to stick in either the open or closed position. Other potential causes of failure include ruptured or leaking valve diaphragms.

Symptoms of Diesel EGR Valve Failure

EGR valve failure can manifest in various ways, with symptoms often resembling those of other engine management component issues. Some common signs of a failing EGR valve include:

  • Check engine light
  • Engine performance issues, such as reduced power, poor acceleration, and rough idle
  • Increased NOx emissions
  • Engine knock or knocking noises in the engine

Troubleshooting Diesel EGR Valves

Performing diagnostics on EGR valves involves following the service manual’s troubleshooting procedures specific to the type of valve in question. However, some general steps can help in diagnosing EGR valve issues:

  1. Read fault codes using a diagnostic scan tool capable of reading fault codes in the EGR system.
  2. Check that all vacuum lines and electrical connections are connected and positioned correctly.
  3. Use a vacuum gauge to check the vacuum supply hose for vacuum at 2000 to 2500 rpm. No vacuum at normal operating temperatures would suggest a loose hose, a blocked or faulty ported vacuum switch or solenoid, or a faulty vacuum amplifier/pump.
  4. Check the vacuum solenoid while the engine is running. On electronically-controlled EGR valves, activate the solenoid with a scan tool and check the vacuum at the end of the pipe. If the solenoid does not open when energized, is stuck in the open or closed position, or has a corroded electrical connection, loose wire or bad ground, EGR operation will be affected.
  5. If possible, check the movement of the valve stem at 1500 to 2000 rpm. The valve stem should move if the valve is functioning correctly. If not, and there’s vacuum, there’s a fault.
  6. Apply vacuum directly to the EGR valve using either a hand vacuum pump or scan tool depending on the type of EGR valve. If there is no change in idle quality, then either the EGR valve is faulty or the passages are completely restricted. If the engine idles rough or stalls, the problem is being caused by a malfunctioning control system.
  7. Remove the EGR valve and check for carbon buildup. Where possible, remove any carbon, being careful not to contaminate the diaphragm.
  8. Inspect the EGR passageway in the manifold for clogging and clean if required.

The Impact of EGR on Diesel Combustion Chambers

The EGR valve plays a crucial role in maintaining optimal combustion conditions within diesel combustion chambers.

By controlling the amount of exhaust gas recirculated into the chamber, the EGR system ensures the correct balance of heat, oxygen, and fuel for efficient combustion.

However, if the EGR valve malfunctions or becomes clogged, it can disrupt this balance, leading to performance issues and increased emissions.

EGR and Fuel Efficiency: A Complex Relationship

While the EGR system aims to improve fuel efficiency by reducing the oxygen level in the combustion chamber, it can also create some challenges.

The cooled exhaust gases introduced by the EGR valve can lower combustion temperatures, potentially leading to incomplete combustion and reduced fuel efficiency. However, the EGR valve’s dynamic operation ensures that when maximum power is needed, the valve closes to provide the necessary oxygen for combustion, maintaining optimal fuel efficiency and performance.


EGR Cooler and Its Impact on Combustion

The EGR cooler plays a crucial role in the EGR system by cooling the exhaust gases before they are reintroduced into the combustion chamber.

If the EGR cooler becomes clogged or fails to receive adequate coolant flow, it can return excessively hot exhaust gases to the combustion chamber, resulting in overheating and reduced fuel efficiency.

In extreme cases, a malfunctioning EGR cooler can also lead to engine damage, emphasizing the importance of proper maintenance and diagnostics.

Oil Leaks and Combustion Chamber Concerns

Oil leaks into the combustion chamber can cause a range of issues, from increased soot and sludge buildup to reduced combustion efficiency and engine performance.

If left unaddressed, these issues can lead to more severe engine damage, making it essential to diagnose and address oil leaks promptly.

EGR and Diesel Knock: A Delicate Balance

A properly functioning EGR system can help reduce diesel knock by maintaining optimal combustion conditions. However, a clogged EGR valve that remains open can lead to increased diesel knock during engine startup and idle.

Monitoring and addressing EGR valve issues is crucial for maintaining engine performance and avoiding potential damage.


The diesel EGR valve is a critical component in modern diesel engines, responsible for reducing emissions and improving fuel efficiency.

(Video) Symptoms of Bad EGR Valve | Signs of Failing Exhaust Gas Recirculation Valve in your car

With its dynamic operation and impact on combustion conditions, understanding the EGR valve’s functionality and troubleshooting techniques is essential for maintaining optimal engine performance.

By staying informed about the role of the EGR valve and addressing potential issues promptly, diesel engine operators can ensure their engines continue to run efficiently and meet emission standards.


When Does EGR Valve Open for Diesel? (Purpose + Solution) | OneStopWheel? ›

The EGR valve is closed when the engine is starting up. During idle and at low speeds, only a small amount of power is required, and therefore only a small amount of oxygen, so the valve gradually opens – it can be up to 90% open at idle.

Does EGR open at full throttle? ›

In general, the EGR valve operates at partial throttle and under 2,500 rpm. It is part of a complex regulated circle steered by the engine control unit. The ECU uses data supplied by various engine sensors and RPM speed to calculate how much exhaust needs to be recirculated and instructs the EGR valve accordingly.

For what reason is the EGR valve opened and closed? ›

Gasoline EGR valves divert the exhaust gases, much like the high pressure diesel equivalent. The vacuum created by cylinder depression, draws the exhaust gases in and the flow is regulated by the opening and closing of the EGR valve itself.

How does EGR valve work in diesel? ›

The EGR system works by returning a small portion of exhaust gas to the engine's combustion chambers through the intake manifold, lowering combustion temperatures and therefore reducing the amount of NOx emitted. The EGR valve is the main component of the EGR system and it's normally closed.

Should an EGR valve be open when cold? ›

On older engines, the EGR valve is closed when the engine is cold. On the new engines, the valve is also open when the engine is cold, so that the warm exhaust gases help to warm up the engine.

At what RPM does the EGR valve open? ›

If possible, check the movement of the valve stem at 1500 to 2000 rpm. The valve stem should move if the valve is functioning correctly – if not, and there's vacuum, there's a fault. Apply vacuum directly to the EGR valve using either a hand vacuum pump or scan tool depending on the type of EGR valve.

What commands the EGR valve to open? ›

The EVP sensor also helps with self-diagnostics because the computer looks for an indication of movement from the sensor when the it commands the EGR valve to open or close. The sensor works like a throttle position sensor and changes resistance. The voltage signal typically varies from 0.3 (closed) to 5 volts (open).

What will happen if the EGR valve opens at idle? ›

Engine performance issues: if the valve is stuck open the vehicle's air-fuel ratio will be disrupted causing engine performance issues such as reduced power, poor acceleration and rough idle. It may also produce turbo boost pressure leaks, causing the turbo to work harder.

Why should the EGR valve remain closed at idle and at full throttle? ›

during full acceleration), the EGR valve closes to ensure as much oxygen enters the cylinder as possible. EGR valves can be used to improve combustion efficiency and knock tolerance. In diesels, it can also help to reduce diesel knock at idle.

What sensor controls the EGR valve? ›

EGR Fraction Based Control

Critical sensors are an exhaust manifold pressure sensor (P2), an intake manifold pressure sensor (P2) and a speed density estimate of total mass flow. Exhaust and intake manifold pressures are used to control the EGR valve and VGT vanes.

Can a diesel run without a EGR valve? ›

So without EGR the Engine will run Hotter. There is an increased stress and pressure on the cooling system. which when fails can destroy an engine within minutes.

Can you drive a diesel without the EGR valve? ›

Technically you can drive without a working EGR valve.

It won't affect the health of your engine, but it will hurt the environment. The role of your EGR valve is to reduce the number of toxic NOx gases in the air, so if it isn't working quite right, more toxic gases will be released into the air.

At what temperature does EGR valve operate? ›

DieselGasoline (direct-injection engine)
Exhaust gas temperature when the EGR system is active450°C450°C to 650°C
Why is an EGR system used?To reduce nitrogen oxide, soot particles, and noiseTo reduce nitrogen oxide and fuel consumption
1 more row

What is the difference between hot EGR and cold EGR? ›

Hot EGR can reduce HC emissions due to the available temperature inside the combustion chamber some carbon particles burn to release energy. But cold EGR reduces the temperature of the combustion chamber so HC emission is more when compared with hot EGR.

Does EGR go before or after Turbo? ›

The regular EGR system we are all used to, is commonly referred to as High Pressure EGR (HP EGR), or sometimes referred to as Short Route EGR. This utilises exhaust gas in the exhaust manifold, before the turbine, routed into the intake manifold, after the turbo compressor.

What pushes air through EGR valve? ›

The valve opens when required to reduce the overall oxygen content of your air/fuel ratio. The pressure from the exhaust gas pushes the gas through the valve to be sucked into the cylinder.

What is the purpose of circulating coolant through the EGR? ›

Abstract: Exhaust gas recirculation (EGR) is an effective strategy to control NOx emissions from diesel engines. The EGR reduces NOx through lowering the oxygen concentration in the combustion chamber, as well as through heat absorption.

How does EGR cooling system work? ›

So, what does an EGR cooler do exactly? After combustion, the cylinder's exhaust valve opens and the waste gas flows through the exhaust manifold into the EGR cooler. In the cooler, the antifreeze coolant lowers the temperature of the exhaust before it cycles back into the engine.

Does removing EGR increase power? ›

When an EGR delete works properly, it increases the oxygen density in the engine. That means a boost in horsepower. However, it is essential to consider how much of an increase you get. Usually, it is minimal.

What is the most common causes of EGR failure? ›

The failures are usually caused by a build-up of deposits in the EGR valve over a period of time that causes them to stick. This build-up is part of the ordinary operation of the vehicle and should be regarded as a serviceable item requiring repair or replacement.

Does throttle position affect EGR? ›

A faulty throttle body: This regulates the air inlet into the combustion chambers. The malfunction of the throttle body can also affect the EGR valve.

What happens when the EGR solenoid is activated? ›

When the EGR control solenoid is activated, a passage is opened up that allows exhaust gases into the intake manifold. The EGR solenoid is controlled by the engine computer, and activated at very specific times in order to achieve the best performance, efficiency, and emissions from the engine.

What is the most common cause of a p0401 EGR code? ›

These common causes may include a clogged EGR valve that can no longer allow the correct flow of exhaust gasses, a faulty EGR valve due to the low vacuum coming from the EGR control solenoid, or an EGR that can not hold the vacuum.

Will a blocked EGR affect Turbo? ›

The EGR valve is likely to stick and become coked up on some applications. This can have a significant effect on the performance of the turbocharger. A faulty EGR valve can result in excessive carbon/soot at the turbine end. This could cause the VNT mechanism to stick.

How often does EGR valve open? ›

EGR stands for exhaust gas recirculation. Therefore, the valve is a type of emissions-control device that is located between the exhaust manifold and the intake manifold. This is normally closed by the time you turn on the engine. However, once the engine heats up and under load, the valve will eventually open up.

How do you prevent EGR valve problems? ›

Moreover, many EGR problems can be avoided by simply ensuring that the vehicle is maintained regularly and gets a decent blat down a highway at least once a month, with plenty of accelerating and decelerating (pottering around town at low speeds is especially bad for EGR valves).

What does an EGR delete do on a diesel truck? ›

An EGR delete kit is an aftermarket performance part that removes the EGR valve and prevents exhaust from being redirected back to the engine. Ultimately, this allows your vehicle to function as if it never had an EGR valve.

How does EGR affect diesel combustion? ›

The EGR takes the exhaust from the combustion chamber, cools it in the EGR cooler, and returns part of it to the combustion chamber. This cooled exhaust replaces some of the oxygen that would normally be used to burn the fuel. This burns any diesel remaining in the exhaust, reducing NOx emissions and fuel consumption!

What damage can a faulty EGR valve cause? ›

If your EGR valve gets stuck in the closed position, then this can lead to a build up of heat within the engine, which can cause the air fuel mix to ignite prematurely. This early combustion, which will be especially noticeable at low revs, is likely to create a knocking sound.

What cools an EGR valve? ›

Pre-turbine (HPL) exhaust is routed via an EGR control valve and an EGR cooler to the engine inlet system. Engine jacket water is used as the cooling medium in the EGR cooler in this example as well. In general, EGR can be cooled with engine coolant, ambient air or a low temperature liquid.

Is it better to clean or replace EGR valve? ›

Sometimes simply cleaning the valve is a better, cheaper alternative to replacing the valve; however, you should make sure that cleaning the valve will fix the problem, and that the actual issue is not being caused by the part being cracked or broken internally.

Can blocked EGR cause overheating? ›

Engine overheating: if coolant flow is restricted, the EGR cooler is unable to cool the exhaust gases. This not only allows NOx emissions to continue, it also causes overheating which can cause serious damage.

Does coolant run through EGR valve? ›

The EGR cooler is a water to air heat exchanger that sits between the turbo and the EGR valve. The body has a hollow tube or series of tubes for the hot exhaust gas to pass through. Surrounding these tubes, are several coolant passages.

How do you unclog a EGR cooler? ›

Ultrasonic cleaning is an effective way to clean EGR coolers because it removes all types of deposits, including soot, carbon buildup, and other residues. It can also be used to clean other parts of the EGR system, including the EGR valve, as well as a range of other engine components.

How often should you replace the EGR cooler? ›

Experts recommend replacing the EGR cooler of a vehicle every 80,000 miles, depending on the make and model of the vehicle. However, EGR coolers are one of the most expensive parts of an engine and replacing them may not be a viable option for many individuals.

How do you tell if an EGR valve is stuck open? ›

Open Position: Rough idling and problems with acceleration are the two most common indicators that the EGR valve is stuck open. The truck might also stall excessively. When the EGR valve is stuck open, all of the exhaust gas cycle back into the chamber, meaning there's not enough oxygen for a combustion to take place.

Is a EGR closed when car is off? ›

When the engine is off, the EGR valve closes and remains so. The EGR valve has been a problem area on older vehicles. This pollution-control device is designed to redirect controlled amounts of exhaust gas back into the intake manifold to be burnt off and reduce NOx emissions.

What controls EGR flow? ›

The EGR flow rate is controlled by the VGT vane position while boost pressure is controlled by EGR valve position [2501] [2502] . EGR flow must be controlled by the VGT because EGR flow is not monotonic with respect to EGR valve position [2493] .

What are the symptoms of excessive flow in EGR? ›

An EGR that has excessive flow can cause the engine to hesitate or stall on acceleration or have a very rough engine idle. The Check Engine Light on will cause the vehicle to fail emission testing. If the catalyst is blocked causing code, then it could cause engine to lose power or not start.

Does EGR valve affect acceleration? ›

A faulty EGR valve can cause problems with the flow and operation of the EGR system leading to performance issues including a reduction in power, reduced acceleration and decreased fuel efficiency. It can also cause vehicle emissions to increase.

Can a EGR valve cause hesitation? ›

A clogged or malfunctioning EGR valve can disrupt the vehicle's air-fuel ratio, which can cause engine performance issues such as a reduction in power and fuel efficiency. The vehicle may also stall or hesitate while accelerating.

What would happen if the EGR valve is stuck closed? ›

If the EGR system is clogged up, or the valve is stuck closed, the combustion temperature increases. This may cause pinging (detonation), as well as surging on light acceleration. In a diesel engine, a bad EGR valve is one of the causes of a black smoke. The Check Engine light might also come on in either case.


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