symptoms of a bad egr valve

A properly functioning EGR valve helps to both cool the engine while also helping to reduce harmful emissions in the exhaust. Though carbon deposits and other physical faults can affect the EGR’s ability to function properly.

A bad EGR valve can cause increasingly worse problems with the engine such as a worsening rough idle, high fuel consumption, and poor acceleration. While these problems might start out minor, they can worsen in short-order putting you at risk of causing more serious damage to your car’s engine and exhaust system.

If you suspect that you have a bad ERG valve, there are a few things you can do to troubleshoot the problem and determine what can be done about it. This often starts with delving into a deeper understanding of how to read the signs of a bad EGR valve.

In this article, we will outline key indicators that suggest your car’s Exhaust Gas Recirculation (EGR) valve is on the verge of failure and provide guidance on the necessary steps to address the issue.

In this article, we will outline key indicators that suggest your car’s Exhaust Gas Recirculation (EGR) valve is on the verge of failure. Additionally, we will provide expert tips on how to test and clean the EGR valve effectively, allowing you to tackle the issue like a professional.

What Is an EGR and How Does It Work?

What Is an EGR and How Does It Work?

The EGR valve in a gasoline engine is connected to both the car’s exhaust manifold and the air intake manifold. When fuel and air are burned in the combustion chamber, some of the exhaust gases pass through the EGR valve, which redistributes the gases back to the air intake manifold via a secured vacuum line.

This helps to regulate the engine temperature, while also reducing environmentally harmful emissions that pass to the exhaust system. Cars with a properly functioning EGR valve tend to have much lower nitrogen oxide (NOx) emissions in the exhaust. Whereas cars with a bad EGR valve often fail emissions tests.

8 Surefire Signs of a Faulty EGR Valve You Shouldn’t Overlook

The early signs of a bad EGR valve are often subtle, starting out as a slightly hard idle, and slightly lower MPG. Though as time goes on, they can worsen causing much more serious symptoms while also increasing the risk of engine damage. You can often use the signs of a failing EGR valve to help determine the necessary repair.

Here are eight key indicators that your car’s EGR valve is bad and about to fail and what to do about it:

1. A Rough Idle

A Rough Idle

One of the earliest signs of a malfunctioning EGR valve in your vehicle is difficulty starting the engine or instances of it stalling, particularly when the engine is cold, or when the vehicle is idling or driving at low speeds. If the EGR valve remains stuck open, it results in an improper amount of gases in the combustion chamber which disrupts the fuel-air mixture and negatively affects the engine’s performance.

Sometimes may notice that your vehicle’s idle feels a bit rough at times, then it seems to smooth out, only to return to being rough. This can be a roller coaster of relief and concern as the faulty EGR valve intermittently gets stuck open.

As the stretches of rough idle grow longer and longer, the bad EGR valve often leads to the engine stalling. This can be a real issue as it often stalls when you’re stuck sitting for a long time at a red light or sitting in stop-and-go traffic.

2. Poor Acceleration

Poor Acceleration

One of the first signs of a problem with the EGR valve is engine performance issues. When the EGR valve starts to malfunction, it can negatively impact your car’s engine performance. Symptoms of a bad Exhaust Gas Recirculation valve may include decreased power during acceleration, delayed throttle response, and an overall lack of agility in your vehicle’s functionality.

Additionally, an increasingly uneven idle might be noticeable as the Engine Control Unit (ECU) struggles to balance the fuel-air mixture when the engine is under significant load.

So, if your car’s feeling a bit sluggish and the idle seems off, it might be worth getting that EGR valve checked out.

3. Occasional Misfires

Occasional Misfires

As a bad EGR valve worsens the imbalance in the fuel/air mixture results in unburned fuel deposits that can cause misfires. The longer the problem persists the more often misfires will happen, and the more risk you will be at for damaging your engine as well as your exhaust system.

4. Running Hot & Overheating

Running Hot & Overheating

A bad EGR valve makes it hard for the engine to regulate its heat, causing it to run hot all the time. If you’re driving for a long time, or you get stuck in heavy stop-and-go traffic the engine can start to overheat. In a severe case of overheating the cylinder head, head gasket and other critical engine components can then be damaged as a consequence of a bad EGR valve.

5. Poor Fuel Consumption

Poor Fuel Consumption

A faulty EGR valve can have a negative impact on your car’s fuel economy, as it may result in the burning of more fuel than necessary. When the EGR valve is stuck open, it fails to properly recirculate the appropriate amount of exhaust gases. This leads to an imbalanced air-fuel mixture, often resulting in a decline in MPG (miles per gallon) performance.

As the fuel economy continues to drop, the number of misfires caused by unburned fuel in the engine and exhaust system tends to increase in proportion. If you notice a sudden drop in your vehicle’s mileage or find yourself making more frequent visits to the gas station, a bad EGR valve could be a contributing factor.

6. Fuel Odors

Fuel Odors

Unburned fuel caused by a bad EGR valve can cause fuel odors to emanate from the engine bay. In time, you’ll start to smell them outside the car, inside the engine bay, and eventually in the cab of the car itself.

7. Engine Knocking Noises

Engine Knocking Noises

Distinctive engine noises like knocking or pinging can be potential indicators of EGR valve malfunctions. A faulty EGR valve can occasionally get stuck in a closed position, resulting in an increase in engine block temperature and leading to premature fuel ignition. This condition elevates the risk of early combustion, creating knocking sounds especially noticeable at low RPMs. As the engine continues to heat up, these knocking noises can become increasingly intense.

8. The Check Engine Light Comes On

The Check Engine Light Comes On

One of the primary indicators of a bad EGR valve is the illumination of the check engine light on your car’s dashboard. This can be triggered by the fuel-air imbalance caused by a malfunctioning EGR valve, leading the Engine Control Unit (ECU) to signal a warning. A bad EGR valve typically triggers specific error codes, such as P0400 for EGR flow malfunction. You might also get code P0401 for EGR insufficient flow detected if the EGR valve is stuck closed or code P0402 for EGR excessive flow detected if the bad EGR valve is stuck open.

4 Expert-Approved Methods to Test Your EGR Valve

To properly test for a bad EGR valve, you’ll need to perform a vacuum test as well as a manual inspection to determine the state of all the moving parts. This starts with locating your EGR valve.

Where Is My Car’s EGR Valve?

Where Is My Car’s EGR Valve

The EGR valve in most modern vehicles can be found on the top of the engine. It looks like a roughly 3-inch diameter valve with a vacuum line running from it to the air intake manifold. If you can’t immediately find it, check your car’s service manual.

1. Manually Assessing the Diaphragm for Carbon Deposits

Manually Assessing the Diaphragm for Carbon Deposits

You can manually test the valve stem and diaphragm of a suspected bad EGR valve via the following steps.

  • Step One: Access the valve and check the opening on the bottom of the metal disc.
  • Step Two: Insert a finger inside the opening to feel for the diaphragm.
  • Step Three: Try to move the diaphragm up and down with the pressure of your finger alone

If you can’t move the diaphragm at all, then you likely have carbon deposits restricting plunger movement within the EGR valve.

2. Testing the Integrity of an EGR Diaphragm

Testing the Integrity of an EGR Diaphragm

If the diaphragm could move, or your finger test felt like there was a fault with the diaphragm itself, you will need to test for potential air leaks. You can do this via these steps.

  • Step One: Set the parking brake and/or block the car to prevent it from moving at all.
  • Step Two: Start the engine and give it a minute or two for the RPMs to stabilize.
  • Step Three: Attach a small applicator stray to a can of carburetor cleaner and spray a little into the opening at the bottom of the EGR valve.

If the RPMs immediately jump up, it means there’s an air leak and the engine was able to burn some of the carb cleaners.

3. Testing for Stem Movement

Testing for Stem Movement

Let the engine run for another minute or two to clear any residual carb cleaner from the system. You can then test the stem for movement with a small hand mirror and the following steps.

  • Step One: Have someone else step on the accelerator to hold it at 2,500 RPMs.
  • Step Two: Use a small hand mirror to watch the diaphragm.
  • Step Three: If you don’t see the stem moving, detach the vacuum hose that leads to the car’s air intake.
  • Step Four: Place your finger on the end of the hose to seal it off. You should feel the vacuum pulling on your fingertip.
  • Step Five: Have the other person increase the RPMs to 3,000 and see if the vacuum gets stronger. If it doesn’t then you likely have a fault in the EGR’s control circuit.
  • Step Six: Reconnect the hose.

4. Testing a Bad EGR Valve with a Vacuum Pump

How to Test EGR valve, Vacuum test, manual test

If you own a vacuum pump tester, or you can rent one from your auto parts store, you can use it to test the integrity and performance of your suspected bad EGR valve via the following steps.

  • Step One: Let the engine come down to a stable idle.
  • Step Two: Disconnect the vacuum hose and plug it with something like a screwdriver tip or chopstick.
  • Step Three: Connect the vacuum pump tester to the EGR valve in place of the vacuum hose. Then set it to apply 15 in-Hg of vacuum.
  • Step Four: Watch the diaphragm for movement and listen for any changes in the RPMs.

If the diaphragm doesn’t move or the valve itself can’t hold the 15-Hg of vacuum, you’ll need to completely replace the bad EGR valve.

If the engine idle remains the same, but the plunger moves and the diaphragm is able to consistently hold the 15-Hg of vacuum, then you probably have carbon buildup blocking the EGR passages. You might be able to clean it. Though it might be equally wise to replace it altogether.

Step by Step guide to clean a dirty EGR Valve

How to CLEAN your Car EGR valve & Electronic EGR Valve Testing (AFTER): Honda EGR Valves P0401 P0402

If you’ve inspected and tested the EGR valve, the diaphragm is intact, and you think you can correct the problem by simply cleaning away the modest carbon buildup with some throttle body cleaner and the following steps.

  • Step One: Carefully remove the rubber vacuum line from the EGR valve. If it looks brittle or frayed, you might want to replace the vacuum hose as well.  
  • Step Two: Disconnect the wiring harness from the EGR valve and pull it out of the way. It’s a good idea to cover it with something to keep it from accidentally getting sprayed.
  • Step Three: Remove the bolts that anchor the EGR valve to the engine.
  • Step Four: Pull out the diaphragm and inspect it again for good measure.
  • Step Five: Use the throttle body cleaner spray according to the manufacturer’s directions. Most advise spraying the EGR valve on and letting it soak for at least 10 minutes.
  • Step Six: Try to remove the carbon deposits from the EGR valve with an old toothbrush and pipe cleaners. You might have to repeat this step several times.

If the EGR valve is badly caked, you might have to soak it in carb cleaner overnight. Just be sure to keep any electrical connections out of the carb cleaner.

  • Step Seven: Reinstall the EGR valve in the reverse steps.
  • Step Eight: Start the car, let the RPMs normalize, and take it for a short test drive to see if the problem has cleared up.

EGR Valve Replacement Cost: What You Should Expect to Pay?

EGR Valve Replacement Cost

If the bad EGR valve has a damaged stem or compromised diaphragm, or it’s simply beyond what the throttle body or carb cleaner can remove you might need to completely replace it.

The cost to have a mechanic replace a bad EGR valve ranges from around $250 to $350. Of this, around $180 to $250 is the cost for the part itself.

Frequently Asked Questions

Can I Just Replace the Diaphragm Inside a Bad EGR Valve?

It is possible to just purchase a replacement diaphragm and install it if you found that the bad EGR valve was a leak in the plunger itself. However, there could still be problems with the stem, the vacuum hose, or other elements of the EGR valve. If cleaning doesn’t help, or the diaphragm is compromised, the smarter move, in the long run, is to completely replace the bad EGR valve.

Is It Safe to Drive with a Bad EGR Valve?

If you’ve just started noticing symptoms of a bad EGR valve, like a rough idle, and slightly poor MPG, you might be able to drive the car for a week or two while you save up for the repair or you have the time to test and fix it yourself.

If the bad EGR valve is causing stalls, overheating, and misfires, then it’s best to let the car sit until you can get it fixed properly. Driving with a bad EGR valve can damage your engine and exhaust system in very expensive ways. Not to mention the very real risk of getting stranded somewhere.


The early signs of a bad EGR valve, like a rough idle and poor MPG are easy to miss at first. Though as the idle gets worse, the engine starts overheating and you experience misfires or stalls, then the bad EGR valve needs to be fixed.

Simple manual tests can help you determine if the problem is a fault in the EGR valve’s diaphragm, the stem, or a buildup of carbon deposits. It might be possible to clean a bad EGR valve with carb or throttle body cleaner. Though a badly damaged diaphragm, or a bad stem, the wisest fix is to completely replace the EGR valve.

This is something you can do yourself for $180 to $250 for the part, and the better part of a Saturday afternoon. Though a mechanic can replace a bad EGR valve for $250 to $350.

Jason Farrell

Written By

Jason Farrell

Jason Farrell is a certified master technician, the editor of Mechanic’s Diary in Pittsburgh, Pennsylvania. He is ASE (Automotive Service Excellence) certified and earned a Bachelor’s Degree in Automotive Technology from Pittsburg State University. With nearly 18 prior years of experience in the automotive field, he has extensive knowledge about Domestic, European, and other foreign makes and models of cars and light trucks. Jason’s experience working as a technician and service manager at dealerships, gave him the experience and know-how of most aspects of inspection, diagnosis, and repair from engine and drivability to electrical, HVAC, brakes, steering and suspension and everything in between.

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