What Happens When an Egr Valve Goes Bad?

Written by john albers | 13/05/2017

EGR stands for Exhaust Gas Recirculation. This type of valve is commonly found on any model gasoline or diesel vehicle produced since 1984. It functions to reduce the levels of nitrogen oxide a vehicle puts into the atmosphere. Nitrogen oxide is a compound that is the chief component in acid raid and smog; it is both a carcinogen and known to cause many severe respiratory disorders in human beings. The EGR valve funnels a portion of the engine’s exhaust back into the engine’s combustion cylinders. This second combustion breaks up the nitrogen oxide into its components of nitrogen and oxygen, both harmless elements. It also increases fuel efficiency by generating higher cylinder compression without using more fuel.

What Happens When It Goes Bad?

An EGR valve that goes bad in the open position will result in a vacuum leak. Too much exhaust is being poured back into the combustion cylinders, meaning that there is not enough oxygen for clean combustion. Outwardly this will mean for very rough idling, hesitation during acceleration and engine stalling. If the EGR valve goes bad and gets stuck in the closed position, it will not be able to funnel nitrogen oxide back into the cylinders. This means that nitrogen oxide emissions in the exhaust will rise, and the fuel/air mixture in the combustion cylinders will be too rich. This causes “spark knock,” where the fuel combusts before the optimum moment in the engine’s combustion cycle, throwing off the engine timing.


Leaving the EGR unrepaired will not result in serious damage to a vehicle, although it will increase the rate of wearing in the combustion cylinders and piston heads. Mechanically operated EGR valves can often be removed and cleaned, as the problem is often just a clog somewhere in the valve-head. In the case of electronically controlled EGR valves, clogs are not an issue, meaning replacement is necessary. Most EGR valves are on top of the engine’s inlet manifold and are marked with a large upper case “P” to indicate the back-pressure portion of the valve. Use a ratchet set to remove the bolts and disconnect the valve’s leads from the Powertrain Control Module (PCM). Another EGR is fitted into place and installed in reverse order.

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