Symptoms of a Bad EGR Valve

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An EGR valve can fail in two ways: It can be open all the time, or it can be closed all the time.

If the EGR Valve Sticks Open:

This will cause a continuous flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:

A rough idle upon starting the engine (that is, when the engine is cold) and sometimes at a stop light or while looking for a spot in a parking lot (that is, at low engine speeds in a warmed-up engine).
Stalling when the engine idles.
Increase in fuel consumption.
A slight — or strong — fuel odor while operating the vehicle, because of the increase in hydrocarbons leaving the tailpipe (see the next symptom).
Emissions test failure. When the engine is running at low RPM, lower temperatures in the combustion chambers prevent all the fuel from burning, so the flow of unburned hydrocarbon gases coming out of the tailpipe increases significantly.
The Check Engine light (or Malfunction Indicator Light, MIL, depending on your model) illuminates on your dashboard.

If the EGR Valve Sticks Closed:

This will permanently block the flow of exhaust gases into the intake manifold. You'll notice one or more of the following symptoms:

A pinging or tapping noise coming from the engine at low RPM (at speeds higher than idle). The noise is the sound of early ignition of the fuel when it meets high temperatures.
Loud detonations. A second ignition can happen after the normal ignition, and the two can combine with enough power to potentially cause serious engine damage.
Your car fails the emission test. High temperatures in the combustion chamber allow the excessive formation of oxides of nitrogen, which are released through the tailpipe.
The Check Engine light, or Malfunction Indicator Light (MIL), illuminates on your dashboard.

Are the symptoms above a sign of EGR problems?

Not necessarily.
An increase in hydrocarbon emissions isn’t necessarily caused by a stuck-open EGR valve. Problems in other systems may cause this same symptom as well: a leaking fuel injector, bad ignition timing, bad cylinder compression, bad oxygen sensor, or other problems.

Similarly, an increase in NOx may be caused by a vacuum leak, a clogged fuel injector, low fuel pressure, a leaking head gasket, or other problems.

A rough idle may be caused by a faulty ignition coil, a vacuum leak, or an ignition system problem.

Because these symptoms vary and be caused by different issues, don’t hesitate to troubleshoot the EGR valve and other system components to try to narrow down the problem. This article, How to Test an EGR Valve, gives a series of troubleshooting procedures on vacuum and electrical vacuum-controlled EGR valves, and will help you find out if the problem is your EGR or something else.

Also, because cars with electronic EGR valves will have a Check Engine or MIL light on the dashboard, in these cars you can find out what engine system malfunction triggered the light. With an aftermarket scan tool, you can pull the trouble codes from the computer's memory and see what system or components are causing the problem. Then, you can try to find the fault with the help of the vehicle repair manual for your particular car make and model.
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