How to Test an EGR Valve - A Simple Procedure


Learning how to test an EGR valve will save you time, money and some headaches. After miles of service, the exhaust gas recirculation (EGR) system — especially the EGR valve — will lead to engine performance problems due to carbon buildup, components mechanical problems, or vacuum hose leaks.

Depending on the particular problem, you'll notice symptoms like rough idle, pinging or knocking engine sounds, an increase in emissions, poor fuel economy, hard starting and even stalling.

Without some troubleshooting, though, these same symptoms will mislead you into replacing an otherwise good EGR valve, solenoid, or miss a simple solution to your problem.

Here, we take a look at a simple procedure to troubleshoot a potential bad EGR valve, and a few tips to do some system cleaning, if necessary.

In either case, I'd recommend you buy the vehicle repair manual for your particular make and model, if you don't have one yet. The manual will help as a reference, either now or later, to identify the exact type and components you have in your EGR system; help you in identifying passageways for cleaning the system, including the valve itself; and the correct steps if you need to replace the EGR valve. Not to mention all the help you'll get in future maintenance and repairs for your vehicle.

You can get fairly inexpensive aftermarket repair manuals from most auto parts stores or online. Or, if you don't want to buy the manual now, look up a copy of the manual in the reference section of your local public library.

And one more thing. Here, we'll deal with vacuum controlled EGR valves found in old model vehicles and some newer models using hybrid (vacuum-electronic) controls.

New vehicle models come with electronically controlled valves, though (about six different types of EGR-valve control configurations exist today, and some late model cars have rid of the EGR valve entirely). Still, you can follow this guide along with the procedure described in your vehicle manual to test your EGR valve, if necessary.

To apply one of the tests to the EGR valve, you'll need a vacuum pump, which you can borrow-rent from a local auto parts store, if you don't have one. Other than that, you'll only need to use some common tools if you need to clean carbon buildup from EGR system passages.

Before testing, though, let's take a look at the purpose of the EGR system and what the EGR valve does, to make better sense of the EGR valve testing procedure.

EGR valve with carbon buildup.
EGR valve with carbon buildup. | Source

What Does the EGR System Do?

The EGR system in your vehicle uses the EGR valve to introduce measured amounts of exhaust gases back into the combustion chambers. These gases lower combustion temperatures. And lower combustion temperatures mean lower emission of harmful NOx (oxide of nitrogen) gases.

However, exhaust gases shouldn't flow continuously into the cylinders. Once the engine has reached operating temperature, gases begin to flow gradually as engine speed increases. When this flow pattern fails, you begin to notice a decline in engine performance. For instance, this will happen if the EGR valve fails to close completely as the engine idles, or fails to open when engine speed increases.

Unfortunately, problems in the EGR system and valve will happen sooner or later. Overtime, small carbon particles contained in the exhaust gases begin to stick and accumulate along EGR and intake system passages, clogging tubes, exhaust gasses channels and the EGR valve itself. Eventually, this will affect the valve's plunger mechanism as well, causing it to stick open or close. On top of that, EGR parts and components wear out and stop functioning properly.

That's when troubleshooting becomes necessary. You need to confirm whether the EGR valve has failed or carbon deposits have began upsetting EGR system and engine operation.

How to Test an EGR Valve

Locate the EGR valve

Look for a round, thick, metal disc about three inches in diameter. In most cases, you'll find it around the top area and to one side of the engine. You may need to look between and under some components on your vehicle. Also, you should see a thin, vacuum line connected to the top of the valve.

Still, depending on your vehicle model, the valve itself may have a different configuration. If you have trouble locating the valve, consult your vehicle service manual. Or visit an auto parts retailer on the Web, and enter your vehicle information to look for the EGR valve. Many auto parts stores online keep a database of auto parts photos or images for many vehicle makes and models. You may find a picture of the EGR valve for your particular model. That way you'll know what to look for.

Testing the Valve Stem Manually

The valve's metal disc houses a diaphragm, spring, and plunger to maintain the valve in the normally closed position. During operation, increase in vacuum pulls on the diaphragm, overcoming spring pressure to open the valve.

If you have good access to the valve, you may see small openings on the underside of the metal disc.

* Try to push on the diaphragm by sticking a finger through one of the openings of the EGR valve, if you have access to it — if you can't reach the diaphragm don't worry, you still can test the valve in the following sections.

* If the diaphragm doesn't move at all using finger pressure, you need to inspect EGR valve passages for carbon deposits restricting plunger movement (check the section EGR Valve and System Passages Cleaning below), or the mechanism has failed.

Testing EGR Valve Diaphragm Condition

Valve diaphragms suffer wear and tear as well. Eventually, they may start leaking exhaust gases. However, hidden from view inside the valve case, you need to do a specific and simple test to know the condition of the diaphragm.

* Apply the parking brake, block the wheels, and start the engine.

* Using a can of carburetor cleaner with the thin straw inserted into the tip, carefully spray a small burst of cleaner through the underside openings and towards the diaphragm.

* If the engine's rpm increases as you spray carburetor cleaner into the valve, the diaphragm is leaking and you need to replace the valve.

Testing for Stem Movement

Start the engine and let it idle for about 15 minutes to bring it up to operating temperature.

* With the engine at idle, increase engine speed to about 2,500 rpm by quickly pushing and letting go of the accelerator linkage by hand, or ask an assistant to do it for you by quickly pressing and releasing the accelerator pedal.

* As you do this, watch the valve diaphragm movement. Use a small hand mirror for this, if necessary.

* If the stem or diaphragm doesn't move, disconnect the thin vacuum hose from the top of the valve.

* Place your finger on the opening of the vacuum hose you just disconnected.

* Increase engine rpm again as you did in the previous step. You should feel vacuum or a slight pressure on your finger tip, depending on the particular system type.

* If you don't feel a change in vacuum or pressure, likely the problem lies with the circuit that provides vacuum or pressure to the valve.

* Reconnect the vacuum hose to the valve.

Testing Valve Operation With a Vacuum Pump

* With the engine idling at operating temperature, disconnect the vacuum hose from the valve and plug it with a thin Phillips-head screwdriver or a similar object.

* Connect a hand vacuum pump to the EGR valve in place of the vacuum hose and apply 15 in-Hg of vacuum to the valve (if you don't have access to a vacuum pump you may borrow-rent one from a local auto parts store).

* As you apply vacuum to the valve, check for diaphragm movement. Also, pay attention to engine idle. Idle should become rough or the engine should stall as you apply vacuum.

* If the plunger doesn't move or the valve doesn't hold the vacuum you apply, replace the valve.

* If you notice no change at all in engine idle operation, but the plunger moves and the diaphragm holds vacuum, carbon buildup is blocking passages in the EGR system or the valve itself. Continue with the following section to remove the valve and clean the passages.

Common Vacuum Type EGR System Checks
* EGR valve plunger movement
* EGR valve diaphragm leaks
* Vacuum check
* Vacuum hose condition
* EGR system passages obstruction

EGR Valve and System Passages Cleaning

If you suspect carbon deposits are blocking the EGR valve or system passages, remove the valve. You can also remove carbon deposits from some electronic EGR valves.

Tools You'll Need:

* Set of sockets
* Ratchet
* Ratchet extension
* Adjustable or crescent wrench, if necessary
* EGR valve or carburetor cleaner
* Dull scraper
* Wire brush

Removing the valve:

* On some models, you only need to remove two mounting bolts. On other engines, you may need — in addition to removing the two mounting bolts — to disconnect the valve from a steel pipe that connects the valve to the exhaust manifold.

* Depending on your particular car model, you may also need to remove one or more components to gain access to the valve.

Cleaning the Valve:

* After removing the valve, use an EGR valve cleaner, if possible. However, you can use carburetor cleaner or solvent as well. But don't let the harsh cleaner to reach electronic components attached to the valve or you'll destroy it.

* Apply the cleaner to the passages at the bottom of the valve, intake and exhaust passages.

* Use a dull scraper and wire brush to remove carbon deposits from the bottom of the valve, plunger and valve seat.

* If necessary, replace the valve gasket. If you can't find the valve gasket at your local auto parts store, buy paper gasket and make one yourself.

* Once you've cleaned the valve and passages, reinstall the valve.


Once you know how to test an EGR valve, apply the same steps every one or two years to service the system. Many car manufacturers suggest a specific interval to inspect the EGR valve and system. This simple task will help you keep emissions low, maintain good engine performance, and save on fuel.

Test Your Knowledge of the Automotive EGR System

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1 comment

Lonnie 5 months ago

Was very helpful, Was going to go and buy new one. But after testing. found

that mine was OK

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