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Signs of a Bad EGR Valve

The exhaust gas recirculation (EGR) system is designed to lower vehicle emissions and produce fewer oxides of nitrogen (a major pollutant) by reducing combustions temperatures. The process involves introducing metered amounts of exhaust gas into the engine to create a diluted air/fuel mixture.The diluted mixture burns more slowly and reduces combustion temperatures by up to 300 degrees Fahrenheit.

At the center of the EGR system, is the EGR valve. This device regulates the amount of exhaust gas entering the engine intake manifold.

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Symptoms of a bad EGR valve

The EGR valve is only supposed to allow exhaust gas to enter the engine under certain conditions. EGR is designed to take place when the engine is at operating temperature, under acceleration or part throttle cruise. EGR that happens at the wrong time, or doesn’t happen at all, can result in engine performance problems. These problems depend on whether the valve is stuck open or stuck closed.

EGR valve stuck open: A stuck open EGR valve allows exhaust gases to enter the engine at the wrong time. Common symptoms include of this include:

EGR valve stuck closed: An EGR valve that is stuck closed prevents exhaust gases from entering the engine. This results in increased combustion temperatures. Common symptoms of this failure state include:

  • An illuminated check engine light
  • Spark knock
  • Surging at cruise speeds
  • Increased emissions
Get it diagnosed by a professional

How does an EGR valve work?

Depending on the vehicle, the EGR valve may be either vacuum-operated or electronically-controlled.

Vacuum-operated EGR valve: A vacuum-operated EGR valve uses a pintle attached to a spring-loaded diaphragm. The spring keeps the pintle in place until vacuum is applied to the EGR valve. When this happens, the diaphragm overcomes spring pressure and lifts the pintle off its seat. This allows exhaust gas to enter the engine. The vacuum supplied to the EGR is often regulated by a computer controlled solenoid.

Electronically controlled EGR valve: An electronically-controlled EGR valve is operated by the vehicle’s computer, the engine control module (ECM). The ECM receives input from various sensors throughout the vehicle. It uses this information to determine EGR control. Electronic EGR valves usually have one or more built in solenoids. These solenoids are uses to control the amount of exhaust gas entering the engine.

How to troubleshoot an EGR valve problem

Before condemning the EGR valve, it should be tested. Vacuum-operated EGR valves can be easily tested with a hand-held vacuum pump. Testing of electronic EGR valves typically begins with a diagnostic scan tool. A scan tool will show both trouble codes and live data related to the EGR valve. It may also have a function for remote EGR valve control.

A valve that is found to be bad should be replaced. If EGR-related problems persist after valve replacement, the issue may be the EGR passages in the intake manifold or the EGR controls.

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