EGR Valve Problems: Symptoms, Causes and What Can Be Done

What the EGR valve does

EGR stands for exhaust gas recirculation. The valve lets a controlled amount of exhaust gas back into the intake, where it mixes with fresh air. That lowers combustion temperatures, which reduces the formation of nitrogen oxides, one of the main pollutants from engines.

It is fitted to many diesel engines and a good number of petrol engines too. The engine control unit decides when to open and close it, based on load, speed and temperature. Some valves are operated electrically, some by vacuum, and many have a position sensor so the computer knows what the valve is actually doing.

Why EGR valves stick and clog

Exhaust gas contains soot and oil vapour. When it passes through the valve and the intake passages, a sticky carbon deposit gradually builds up. It can stop the valve closing fully or opening properly, and it can narrow the passages and clog an EGR cooler or intake manifold.

Cars used mostly for short trips are more prone to this, because the engine rarely gets hot enough to burn deposits off. Stop-start town driving, such as short runs around Tyneside, is exactly that pattern. Oil getting into the intake system, worn components and poor servicing can also speed it up.

• Short journeys with little sustained motorway running
• Skipped or late oil changes
• Engine wear that increases oil vapour
• A valve held open or shut by built-up carbon

Symptoms to watch for

The symptoms depend on whether the valve is stuck open, stuck closed or simply sluggish. A valve stuck open lets exhaust into the intake when it should not, which can cause rough idle, stalling and poor pulling power. A valve stuck closed may cause pinking or knocking, more smoke and higher emissions.

• Rough or unstable idle
• Hesitation or flat spots when pulling away
• Loss of power, or the car going into limp mode
• Black smoke or a noticeable increase in fuel use
• Engine warning light with EGR-related fault codes
• Failing the emissions part of an MOT

How the fault is diagnosed

The warning light and fault code are a starting point, not the answer. A code that mentions the EGR system can be caused by the valve itself, but also by a faulty position sensor, a wiring or connector fault, a vacuum leak, a blocked cooler or even a problem with the intake or air flow sensor.

A proper emissions diagnostics check reads the codes, looks at live data such as valve position and commanded versus actual values, and often includes tests of the valve operation. At Banks of the Tyne in Hebburn we can carry out that kind of testing and look at how the exhaust and emissions systems are behaving, so that parts are not replaced on a guess.

Cleaning or replacing: how it is weighed up

In general terms, if the valve is mechanically sound but coated in carbon, cleaning it and the passages can restore operation. If the valve motor, spindle or sensor is worn or damaged, or the deposits are too heavy, replacement is more likely to be the sensible option. Sometimes a cleaned valve sticks again within a short time if the underlying cause, such as short journeys or oil in the intake, has not been dealt with.

We cannot say in advance which route suits your car, because it depends on what testing and inspection show. Ask us and we will explain what we found and why we suggest one over the other. It is also worth knowing that EGR problems can be linked to other emissions parts, such as the diesel particulate filter, so the whole system is worth considering.

Looking after the system

Regular oil changes with the correct grade help keep deposits down. Where you can, give the engine a decent longer run now and then, so it reaches full operating temperature. Do not ignore a warning light or a car running badly, as a stuck valve can lead to further trouble in other parts of the emissions system. If limp mode appears, get the car checked rather than carrying on.

Frequently asked questions