The EGR valve is a centerpiece of a vehicle’s exhaust gas recirculation system. This system is commonly found in diesel-powered vehicles and is used to reduce nitrogen oxides emissions by rerouting a small volume of exhaust gases back into the combustion chamber. This allows for reducing combustion temperatures, resulting in fewer pollutants produced during the combustion process.
The exhaust gas recirculation valve is either computer-controlled or vacuum-operated one-way valve that allows some exhaust gases to enter the intake manifold when the engine needs this most. Normally stuck in the closed position, the EGR valve opens depending on the engine running conditions when it reaches its normal operating temperature. If it opens or closes at the wrong time, you may experience a lack of power, poor acceleration and starting problems.
Vacuum EGR valve
This type of EGR valve relies on a spring-loaded diaphragm and vacuum supplied by the computer-controlled solenoid. The valve features a pintle attached to the diaphragm, which is kept in place by the spring until the vacuum overcomes its pressure, creating a gap that allows exhaust gases to enter the intake manifold.
Computer-controlled EGR valve
As its name says, this electronically-controlled EGR valve is operated by the engine control unit. The latter analyzes data received from different vehicle sensors and sends signals to one or more solenoids built-in the EGR valve. When engaged, the solenoids switch to the open position, allowing exhaust gases to enter the engine via the intake manifold.
There are two common exhaust gas recirculation valve failures. It can stick either in the closed or open position. Let’s see what happens when it fails.
Your EGR valve stuck closed
Obviously, an EGR valve that gets stuck in the closed position prevents exhaust flow into the combustion chamber when the engine needs it. This leads to higher combustion temperatures and causes an illuminated check engine light, increased emissions, knocking sparks, and surging at higher engine speeds.
Your EGR valve stuck open
An EGR valve should be closed until the engine control unit sends signals to the solenoid to open it. However, if it fails in the open position, the exhaust gases will enter the engine as long as it runs, resulting in rough idling, starting problems and stalling, hesitation and stumble. The check engine light will also come on.
EGR valve troubleshooting
Depending on the type of EGR valve you have, its diagnosis may involve either a hand-operated vacuum pump or a scan tool. The latter will allow for reading trouble codes and live data as well as for remote valve control in some cases. A faulty EGR valve must be replaced with a brand-new one. The EGR passages and the intake manifold should also be checked to make sure everything functions correctly.