by James Dreamer

Created on: January 29, 2009

How to Tell if Your EGR Valve Needs to be Cleaned or Replaced

For those not very familiar with cars, let's first describe the function of the EGR valve. EGR stands for "exhaust gas recirculation". The EGR valve controls the flow of exhaust gases into the intake manifold where they are fed back into the engine to be burned again. Why feed exhaust back into the engine? Research has shown that exhaust gases combined with the fuel/air mixture reduces nitrogen oxides (the pollutants that cause smog) and increases the overall efficiency of the combustion process.

So why is there a valve? If exhaust gases help combustion, why not release them into the engine all the time? Under certain circumstances, such as when idling, the fuel and air must be very accurately controlled for the engine to run smoothly. During these periods the presence of exhaust gases would upset this delicate balance and therefore a means of interrupting them must be implemented.

This is the function of the EGR valve. Under conditions when exhaust gases can help the combustion process, it opens and allows the gases to enter the intake manifold. When exhaust would interfere with the smooth operation of the engine, it closes. On modern cars, determining when to open and close the EGR valve is the responsibility of the engine computer.

How can you tell if the valve needs to be cleaned or replaced? Most modern car computers monitor many systems and the "check engine" light will illuminate to notify the driver if there is a problem. At this time it is a good idea to query the computer with a scan tool to determine the exact trouble. If the EGR valve is malfunctioning, an EGR error code will be generated by the computer.

If the "check engine" light does not illuminate or your car does not have a service light, you can still use your mechanical ability to determine if the EGR valve is working. There are two possible malfunctions of this valve. It is either not closing when it should or not opening when it should.

NOT CLOSING. If the valve does not close, the engine will idle rough or stall completely when you remove your foot from the accelerator. It may also hesitate when you try to accelerate. These are the same symptoms as a vacuum leak so don't assume the EGR valve is at fault. You must test it.

NOT OPENING. If the valve does not open, you will notice a small reduction in horsepower. The engine may knock or "ping" under acceleration. It may run a little hotter and seem to labor under load. You may also notice

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