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Exhaust and Car Emission Repairs Home Page > Parts of Car Emissions > EGR Valve

Function: Recirculates some of the engine's exhaust gas back into the intake manifold to be reburned, thereby reducing emissions.

Signs of Wear: Rough-running engine, engine hesitation or stalling, "Service Engine Soon" light illuminates.

The Exhaust Gas Recirculation (EGR) valve is operated by a diaphragm, which opens and closes the valve itself, allowing exhaust gases to enter the intake manifold. Carbon build up can cause the EGR valve to be stuck open, and the feedback circuit (or DPFE) to activate the check engine light. 

The EGR valve is designed to recirculate a small amount of inert exhaust gas in order to cool combustion temperatures and decrease nitrogen oxides. The EGR valve is usually opened when the vehicle is cruising at constant speed. The valve is normally mounted directly on the intake manifold and is controlled by an electronic vacuum regulator (or EVR). In order to operate the EGR vavle, the EVR receives a signal from the engine computer (or ECU) that opens the valve inside the EVR. This directs engine vacuum to the EGR valve. A diaphragm, inside the EGR valve at the same time. This allows exhaust gas to enter the intake manifold. If the EVR fails, it will not allow vacuum to flow to the EGR valve and will cause the check engine light to illuminate.

Carbon can often build-up within the EGR system. This restricts the flow of exhaust to the intake manifold and can leave the system completely ineffective. Carbon buildup can also break apart and lodge in the EGR valve pintle. This keeps the EGR valve open when it should be closed, and will cause the engine to run rough, especially at idle. 

Some EGR systems have a feedback circuit (or DPFE) to determine if the EGR system is working properly. If the EGR valve has been commanded to open and no result is seen, the check engine light will illuminate. Sometimes the DPFE itself can malfunction. The DPFE contains a senseor to measure pressure differences. On vehicles equipped with a DPFE sensor, the tube from the exhaust to the EGR vavale contains a small orifice. WHen there is a pressure difference between the two sides of teh orifice, it indicates the EGR vavle is operating properly. If the pressure sensor fails, the ECU will report that there is insufficient flow through the EGR valve, and the check engine light will illuminate. 

Since the EGR system is connected to the exhaust system, it experiences a great amount of heat. In some circumstances, this heat can melt the EGR tubing, causing it to leak pressure and malfunction. Vacuum lines can also break, rendering the EGR system ineffective.

Have your vehicle's exhaust and emission system checked by an ASE Certified Technician in Exhaust and Emissions. Schedule service today to visit our auto repair facility o the southwest side of Houston.