In my opinion EGR codes are quickly climbing the ladder of the most common causes of check engine light failures to be found on aging automobiles. This is often due to carbon clogging passageways or improper operation of the egr-valve. Common failed components are available below for purchase.
Several technical service bulletins for a wide variety of different makes and models have documented a few different problems associated with the EGR valve system. With some EGR problems you might set a diagnostic trouble code of PO401 or P0402.
You may also set trouble codes for an engine misfire, which would be in the PO300 range. It is also possible your check engine light will not come on and you will just experience a noticeable problem such as rough engine idle or even engine stalling.
A basic explanation of the EGR valve would probably help with the understanding of the diagnosis and repair of EGR codes. Exhaust gas recirculation is necessary for emissions purposes.
Unfortunately when it malfunctions it can actually push emission levels off the chart. The valve meters post combustion exhaust gases to be mixed with the intake fuel charge and this dilutes the mixture.
Allowing exhaust gas to flow into the combustion chamber reduces cylinder temperatures and therefore reduces the amount of nitrogen oxides produced at the tail pipes. Of course this system works hand in hand with other computer controlled on board emissions systems such as the catalytic converter and oxygen sensors to name a few.
When you mix exhaust gases with the air fuel mixture you also have a slower burn of the total fuel charge in the combustion chamber and this can reduce or eliminate engine ping, which is caused by early detonation. This function is not needed at engine idle or when the vehicle is cold.
This is why the EGR system is quite complicated and receives many inputs from other sensors that facilitate its operation. The exhaust gas recirculation valve is solely responsible for metering the amount of exhaust that is mixed with the air fuel charge.
It does this by opening a passage that is sealed by a cone shaped pintle valve. When the pintle retracts exhaust flows from the exhaust system to the intake manifold, often located at the base of the throttle body so it has time to mix with the air/fuel charge.
There are several things that can malfunction in this system that will cause a check engine light failure code to set or cause rough running engine issues. The one I see the most is the passageway from the exhaust to the intake is becoming clogged with carbon deposits.
This causes a condition where no exhaust gas is flowing to the intake manifold or being mixed with the air fuel charge. The repair of this condition is removal of the EGR valve and inspection of the passageway to check for a blockage. Each model vehicle has different procedures for clearing the passageway due to many different configurations of the system. Some Fords have a removable tube.
Another common problem causing failure codes in this system is that the tip of the valve will become irregular shaped from carbon deposits. When this happens it no longer creates a perfect seal.
This can allow exhaust gas to continue to flow when it is not called for by the computer. An example would be at engine idle or when the vehicle is cold. This malfunction can cause a rough engine idle and even a stalling condition. Another EGR problem that I have seen is common on Mazda and Fords.
The failure in these specific vehicles is the development of rust on the pintle shaft that makes the valve hang up and not close properly. The replacement valve has been redesigned to prevent moisture intrusion into the component. In this example, you may set EGR codes. Although there is no specific code for rust on the pintle shaft. This is why some common sense in diagnosis is necessary to solve issues.
Also note that some systems have valve position sensors. You may find a code set for incorrect EGR valve position that may relate to a bad position sensor or actually may be an indication of a valve that is hanging up or has carbon or rust issues.
When I have EGR codes set I go right for ALL-Data, Mitchel's or safecar.gov to see if there is a technical service bulletin that covers the issue. If not I use the diagnostic repair diagram for the specific code set.
This can often help you avoid replacing parts that are good and
wasting valuable time. In the example of a plugged passage way you can
repair this on the cheap. Basically some carburetor cleaner and maybe a
couple of gaskets depending on the year, make and model of the
automobile. Also where they decide to locate the valve.
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