Symptoms of a Bad EGR Valve
Has your EGR valve (your Exhaust Gas Recirculation valve) gone bad? Maybe. I'll tell you the symptoms below. But before you start replacing parts, keep in mind that the same engine performance problems that indicate a bad EGR valve can also indicate problems in other parts of the system. If you don’t do your troubleshooting, you may end up replacing parts unnecessarily and wasting time and money.
This article will tell you several things:
- the symptoms of a bad EGR valve;
- how to start investigating whether the problem is your EGR valve or something else;
- what the EGR valve does and how it works;
- and the different types of EGR valves.
Symptoms of a Bad EGR Valve
Symptoms of a bad EGR valve include:
- rough idling or stalling
- a smell of fuel
- increased fuel consumption
- pinging, tapping, or knocking sounds
- failed smog test
- Check Engine Light on
Valve Stuck Open vs. Valve Stuck Shut
Actually there are two kinds of bad EGR valves, with different symptoms. 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).
- Your car fails the emissions test. 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 cause 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.
Troubleshooting: Is It the EGR Valve or Something Else?
To make things even more complicated, the same engine performance problems that indicate a bad EGR valve can also indicate problems in other parts of the system:
- spark plugs,
- spark plug wires,
- the fuel filter,
- the fuel pump regulator,
- and various engine sensors.
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.
So before spending money and replacing parts, 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.
If your car has an electronic EGR valve, troubleshooting will be easier, because it will have a Check Engine or MIL light on the dashboard, and you will be able to 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. makes good inexpensive aftermarket manuals. Haynes
The EGR's Job: Processing Exhaust Gases
The outside air picked up through the engine's intake manifold contains close to 80 percent nitrogen and 20 percent oxygen, along with small amounts of other elements. When outside air combines with the fuel and ignites in the combustion chamber, temperatures can reach above 2500o F (or 1370o C). Combustion at these temperatures burns the usually inert gas nitrogen, creating oxides of nitrogen (NOx) gases, which cause air pollution and human health problems.
However, when the burned exhaust gases are introduced back into the combustion chamber through the EGR valve, temperatures decrease, inhibiting the formation of NOx gases.
What the EGR Valve Does
The EGR valve is a small component designed to allow the flow of exhaust gases into the intake manifold in controlled amounts. As such, it's a simple valve that closes and opens as needed.
The EGR valve has one single job to do, regardless of the system configuration, type of control and number of sensors: that is, to either open and direct exhaust gases into the combustion chamber, or to close and keep them from entering.
Whenever you start the engine, the valve comes alive and waits in a closed position, blocking the flow of exhaust gases.
Once the engine reaches operating temperature and speed increases, the valve—either through vacuum or electronic control—gradually opens, allowing burned exhaust gases to enter and combine with the air-fuel mixture inside the combustion chamber. If you slow down sufficiently or come to a stop, the valve gradually closes and blocks the flow of exhaust gasses. And the process continues for as long as the engine is running.
After you shut off the engine, the EGR valve closes and remains in that position.
Types of EGR Systems
Gasoline and diesel-powered engines on the road today may use one of several different EGR valve configurations.
- On older vehicle models, you'll recognize the EGR valve as a round, thick metal disc about three inches in diameter, usually towards the top of the engine and on the side. On these older models, a small-diameter vacuum hose operates a basic EGR valve. The hose connects the top of the valve to the throttle body or carburetor. The valve's metal disk houses a vacuum diaphragm, spring, and plunger.
- Later models come equipped with electronic-vacuum EGR valves inside a small block or cylinder. The valve works the same way as in older models, except that an electronic EGR position sensor communicates with the car's computer for better control. You may see electric solenoids connected through vacuum lines to the valve as well.
- Newer vehicle models use electronic EGR systems that may include additional components, even a digital valve that eliminates the need for vacuum control altogether.
- A more radical design, implemented in a few models, was the replacement of the valve with EGR jets at the bottom of the intake manifold.
- Some newer high-efficiency engines, for example those with variable valve timing (VVT), don't even use an EGR system.
Types of EGR Valves
- Vacuum-controlled EGR valve
- Back-pressure EGR valve
- Electronic vacuum-controlled EGR valve
- Digital EGR valve
- EGR jet (in place of EGR valve)
Locating the EGR on a Corvette and on a Truck
A Sensor Related to the EGR on the Ford Focus
Bad EGR valve symptoms vary and resemble problems in other engine systems. But now that you know the type of symptoms a troubled EGR valve will produce, include it in your troubleshooting tests. And restrain yourself from swapping components trying to fix the problem before knowing which part is causing you trouble. Most of the time, you'll just spend time and money unnecessarily. Troubleshoot your EGR valve and other components.
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This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
Questions & Answers
I have a Hino 2011 268, and the SCR malfunction light turns on and off. What is wrong?
There could be an intermittent problem with the SCR system. You may be able to get the codes. This video may give you an idea of how to get the codes yourself:Helpful 33
Why would the EGR valve leak oil?
The oil may come through a seal from the actuator rod which somehow connects to the crankcase ventilation (CCV) system. This seems to be a recurrent problem on some models. You may try replacing the EGR valve and see if the problem doesn't return.Helpful 32
If I have a bad EGR valve, will it throw a code for a misfire in cylinder number 2?
A bad valve most likely will cause a random misfire since it doesn't direct exhaust gases to a particular cylinder. If you are getting a code for the number 2 cylinder, check the injector, spark, or fuel problems for that cylinder.Helpful 26
I have replaced the starter, alternator, fuel pump, spark plugs and wires on my 1998 Jeep Grand Cherokee, but it still won't start or it dies when it does. What else should I do?
Check the fuel pressure and compare it to specs. You'll need the repair manual for your model.Helpful 1
I have had my EGR valve cleaned and then replaced in my 2002 Ford Tauras which has 49,000 miles. Now it idles rough and the check engine light came back on. What could be the issue?
If the trouble codes point to the EGR, then there's possibly something wrong in the system. It depends on the codes. Make sure the circuits (wiring) are checked as well.Helpful 51