European emissions standards made the EGR valve mandatory in contemporary diesel engines; it helps reduce the emission of toxic gas into the atmosphere. As time goes by, the EGR valve may cause certain malfunctions in your diesel vehicle. How does an EGR valve work? Does it have to undergo maintenance? Can it be removed? Take a look at the answers to frequently asked questions by owners of diesel cars.


The term EGR valve stands for Exhaust Gas Recirculation. Invented in the US the EGR valve was first tested by General Motors in the 1970s. It recirculates spent exhaust gas back to an engine’s air intake. The EGR valve is controlled by the vehicle’s central computer: The manufacturer’s rev range determines when the valve opens. Anywhere from 5% to 35% of exhaust gas can be reused, depending on the engine. The EGR valve works once the engine is running at low-load conditions and at a speed of 2,500 rpm. It reduces the amount of NOx emissions in the engine and thus the amount of overall pollution.



There is a reduction in NOx because there is also a reduction in the maximum combustion temperature when gases that come from the engine mix with exhaust gases, which are made up of mostly inert gas. The engine computer controls the EGR valve via a solenoid valve or an electric valve depending on different parameters (water temperature, air temperature, motor load data, slow motion, etc.).

Functional principle

schemaFunctional principle of the EGR valve. When a diesel engine runs at reduced power or slowly, part of the exhaust gas does not get burned. The engine emits an excess of nitrogen oxide and tiny particles into the atmosphere, violating European emissions standards. In an attempt to reduce such emissions, manufacturers install a component with a flap which redirects exhaust gas back into the injection in order for it to get burned a second time. This is the functional principle of the EGR valve. This system, while ingenious, has its downside. Indeed, the EGR valve can become clogged along the injection system. The EGR valve itself can end up completely covered in soot. If the flap of a clogged valve remains closed, your vehicle will function normally, but it will be polluting more. On the other hand, a flap that remains permanently open can seriously damage your intake system. Thus, it is important to properly maintain your diesel vehicle’s EGR valve. In the event of reoccurring problems, in certain cases, you may also consider removing it with the help of your mechanic.

Problems that arise

Unfortunately, this process creates excess hydrocarbons in the form of soot, which builds up in the EGR system, and sometimes even clogs it completely; this can affect the rest of the engine. The engine ends up not functioning as it should due to the unburnt gases which are reinjected into it. The EGR valve starts to malfunction when it is clogged; carbon emissions (soot) build up inside the valve restricting the solenoid valve’s mobility or that of the flap causing complete blockage. The system goes awry, and the engine computer goes into a lower operating mode causing a significant loss of power.

The most common problems include:

  • Loss of power
  • Engine light on
  • Build up on EGR valve
  • Clogged EGR valve
  • Declining technical control
  • The vehicle runs at lower speeds
  • Black emissions

Examples of companies that manufacture EGR valves: Valeo, Valeo EGR Valve, Pierburg, Pierburg EGR Valve, Wahler, Wahler EGR Valve.

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Gasoline vehicles

Certain gasoline vehicles such as some Hondas, the Peugeot 206 1.4l TU3s, 307 2l 16Vs, Alfa 147s, and Opel Corsas, include a gasoline EGR valve which works in tandem with the catalytic converter in reducing NOx.

The EGR valve is more often used in gasoline engines, simply because it enhances performance. Indeed, the gasoline EGR valve helps reduce the combustion temperature and thus improve gasoline engine performance. However, the downside is that this particular valve tends to get clogged due to the unburnt gases that pass through it.


We strongly recommend refraining from removing or blocking your EGR valve. It is against the law to remove an EGR valve. When taking an emissions test, any vehicle missing its EGR valve will systematically fail inspection.

For updates on new technical controls that are to take effect in January 2019, visit our page “All you need to know about the evolution of technical control”.

The best solution

How do unclog/clean your EGR valve without disassembly, without chemical products and in an efficient manner:

If you’re considering a cheap alternative to replacing this part, that’s where the Hy-Calamine device comes in! Your vehicle will go back to its original performance, thanks to this innovative process which uses the solvent powers of post-combustion hydrogen and the unique and patented direct control of the EGR valve known as the “EGR Pilot”! Say goodbye to black emissions, lags in acceleration, loss of power and wasted fuel due to EGR valve build up or clogging.

Functional principle of our EGR valve control system known as the “EGR Pilot”:

Thanks to EGR connectors, the Hy-Calamine device can be directly attached to the EGR valve; its connector simply replaces that of the vehicle.

The device ends up controlling the EGR valve throughout the different phases of the descaling process. The following occurs on a loop:

  • 5 minutes in open position
  • 5 minutes in closed position
  • 5 minutes in back and forth position with 1 second intervals

We can professionally adapt your EGR valve to regulate functional parameters in accordance with the needs of your car.




Before the descaling process with Flex Fuel’s Hy-Calamine device








After the descaling process with Flex Fuel’s Hy-Calamine device