EGR codes

EGR codes are quickly climbing the ladder of the most common check engine light failures.

Several technical service bulletins for a wide variety of different vehicles have documented many different problems associated with the EGR valve system.

When you have EGR valve problems you may set a diagnostic code of PO401 or P0402. You may also set a diagnostic trouble code for engine misfire, which would be in the PO300 range.

It is also possible that your check engine light will not come on and you will just experience a drivability problem such as rough engine idle or even engine stalling.

Exhaust gas recirculation valve

Exhaust gas recirculation is necessary for emissions purposes. The valve meters post combustion exhaust gases to be mixed with the intake fuel charge and this dilutes the mixture.

Allowing exhaust gas into the combustion chamber reduces cylinder temperatures, and therefore reduces the amount of nitrogen oxides produced.

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 pre-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 egr 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 system, usually located at the base of the throttle body.

EGR codes common problems

The one I am seeing the most of 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 vehicle will have a different procedure necessary to clear the passageway due to many different configurations of the system.

This allows exhaust gas to continue to flow when it is not called for, such as at engine idle or when the vehicle is cold. This can cause a rough engine idle and even a stalling condition.

Another EGR valve problem that I have seen is common on some Mazda and Ford vehicles. 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 and diagnosis is necessary to cure exhaust gas recirculation malfunctions.

When I have EGR codes set I go right for ALL-Data 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 avoids replacing un-needed parts and wasting time. In the example of a plugged passage way you can repair this cheap. Basically some carb cleaner and maybe a couple of gaskets.


Give this EGR problems page a Then explore some links.


I know you did not come here to spend $12.95 but for this amount you can print out the repair diagrams, TSB's and procedures for solving egr valve problems for your specific vehicle.

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For more information about how the check engine light operates, why it comes and how to turn it off visit this next page. It takes you from EGR codes to check engine light info

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