The Exhaust Gas Recirculation (EGR) system is used to lower Oxides of Nitrogen (NOx) emission levels caused by high combustion temperature. It does this by allowing some exhaust gas to go back into the intake manifold decreasing combustion temperature.

The main element of the system is the linear EGR valve. The EGR valve feeds small amounts of exhaust gas back into the combustion chamber. With the fuel / air mixture diluted by the exhaust gases, combustion temperatures are reduced.

In newer vehicles the valve is electronically controlled. On older cars and trucks it is controlled by engine vacuum.

EGR Problem Conditions

Too much EGR flow at idle, cruise, or cold operation may cause any of the following conditions to occur:

• Engine stalls after cold start

• Engine stalls during closed throttle conditions

• Vehicle surges during steady throttle cruise

• Rough idle

• DTC P0300 (misfire detected)

Too little or no EGR flow may allow combustion temperatures to get too high. This could cause the following symptoms:

• Engine Spark knock, also known as detonation

• Engine overheating

• Emission test failure

• DTC P0401

• Poor fuel economy

EGR System Repairs

As exhaust gases flow through the EGR all the time, carbon buildup is a problem on the electronic or vacuum style. The diaphram can bind. It is possible to clean out the small pintle on the bottom of the EGR, but usually replacement is needed. Also check the post under the component for carbon buildup as this can block the passage and cause a check engine light or the conditions listed above.