How to Unblock a Catalytic Converter

How to Unblock a Catalytic Converter – and How to Diagnose

Is your check engine light illuminating? Does your car feel sluggish and your fuel economy is worse? It appears you may have a blocked catalytic converter and it’s quite a serious issue that you will need to take care of. But fear not, we’ll be discussing how to unblock a catalytic converter. We’ll also discuss the symptoms you should look out for, as well as how to diagnose, and some possible repair bills you could be facing.

What’s a Catalytic Converter?

Before we learn how to unblock a catalytic converter, it’s good to know more about it first and why it’s important. The catalytic converter is an emission control device in your car’s exhaust system. It helps to reduce your car’s emission by converting toxic gases your engine produces into other gases that are less harmful to the environment. It does this by catalyzing a redox (oxidation-reduction) reaction, but we won’t get too much into detail on that.

Because this conversion is a high heat process, it will cause buildup and clogging in your catalytic converter. This will then lead to several problems since your converter is converting less gas. It can also create backpressure and cause your engine to misfire, among other problems. You can learn more about catalytic converters in the video below:
In a nutshell, the catalytic converter is a crucial part of your car’s exhaust system that controls emissions. If they become clogged, your car can’t work properly. In most cases, a catalytic converter can last for up to 10 years. However, they can become dirty or clogged, in which case you will need to learn how to unblock a catalytic converter.

Symptoms of a Blocked Catalytic Converter

Since they are a crucial part of your car, there are several noticeable symptoms. Here are the signs you might have a blocked catalytic converter:

Performance and Fuel Economy Drop

A blocked converter will convert less gas into your exhaust system. This means less gas can flow through your exhaust system, and this can disrupt performance as well as fuel economy. You will most likely notice the drop in performance as you try to accelerate, where the car feels heavier than usual. Also, this can create backpressure and cause your engine to misfire. In certain scenarios, it can cause your engine to stall as you try to accelerate.

As for the fuel economy, this is because your car gets less oxygen when the converter is blocked. When your car gets less air into the engine, it compensates by injecting more fuel to keep the engine running. As a result, you use more fuel and your fuel economy is worse.

Reduced performance and fuel economy can be caused by other things as well, such as a blown head gasket or bad spark plugs. However, this is a good first indication that you have a blocked catalytic converter.

Your Car Fails an Emissions Test

In some states like Ohio, you will need to do an annual emission test for your car. If your car fails this test, then it’s likely you have a blocked catalytic converter. In any case, cars are designed to meet emission regulations otherwise they won’t be allowed to be on sale in the first place. If your car fails an emission test, then you have something wrong with your exhaust system and you will need to get that checked.

Check Engine Light

The check engine light is a straightforward way your car tells you that there’s something wrong. It usually indicates something wrong with the engine, the transmission, or the exhaust system. And yes, including the catalytic converter. You can identify if there’s a problem with the catalytic converter by scanning the check engine light.

When your check engine light is on, this means the car’s On-Board Diagnostic (OBD) system registers an error code from one of the sensors. When this happens, you can scan the OBD to see the error codes. From that error code, you can identify what exactly is wrong with your car. If you see the code P0420, then there’s a problem with the exhaust system.

We’ll teach you how to diagnose a check engine light so you can find out if it’s the catalytic converter or something else is causing it. But before we do, we’d like to mention the check engine light means that there’s something wrong with the car and it needs your attention. We recommend immediately checking your car if you have a check engine light. Even the smallest problems can lead to more serious damage if ignored.

And if the check engine light is flashing rather than continuously lit, then there’s a major problem that you will need to attend to immediately. We recommend that you stop driving immediately if you see a rapidly flashing check engine light.

Diagnosing a Catalytic Converter

Before you learn how to unblock a catalytic converter, let’s first make sure if there’s actually an issue. As mentioned, if your car fails an emission test then that means there’s something wrong with the exhaust system. Likely with your catalytic converter. Another way to find out what’s wrong is by scanning for error codes. If you experience symptoms and your check engine light is on, we recommend trying this method.

What You Will Need to Scan a Check Engine Light

First and foremost, you will need an OBD scanner or reader. If your car was made after 1996, then your car is likely to have an OBD-2 system. And any car made before 1996 has an OBD-1 system instead. Make sure you buy the correct scanner or otherwise you won’t be able to read your car’s OBD system. An OBD scanner should cost no more than $50 to purchase, or you can buy more complicated ones for hundreds of dollars if you feel like splurging. But you really don’t need anything more than a basic one.

If you don’t feel like spending any money, you can borrow them from someone you know who owns one. Some mechanics or auto shops might be willing to lend it to you for free.

How to Use an OBD Scanner

Now you’ve got your OBD scanner, it’s time to scan your car. Here’s how to do it:

  1. Plug the reader into the car’s OBD port. This port is often located underneath the dashboard area, either above your pedals or knee. Keep in mind that some cars might have their port hidden out of sight. Check your owner’s manual or online to see where it’s located in your car.
  2. Once plugged in, turn on the OBD scanner. It should immediately scan the car. However, some scanners might require you to input additional information such as make, model year, VIN, etc.
  3. It will then display the error codes it has found. A more complicated scanner might also display a description of what’s wrong with the car, but if you have a simpler scanner then it’s recommended to take note of the codes displayed. This way, you can cross-check them with the owner’s manual later on.
  4. If you see the P0420 error code, this means you have a problem with the catalytic converter. We’ll discuss this in more detail soon.

If you see other error codes, then check them with your manual or online to understand what it means. If you need help on how to do this, watch this guide from Car and Driver:

What Does the P0420 Code Mean?

The P0420 code comes on when the sensor recognizes a problem with the catalytic converter’s efficiency. If you have a scanner that displays what the codes mean, it will usually say “Catalyst System Efficiency Below Threshold”. However, this is a generic code and several things might have caused this error code. Including faulty O2 sensors, exhaust leaks, misfires that can damage the converter, and an intake leak. That being said, this problem often indicates a problem with the catalytic converter. Either the converter is damaged and needs to be replaced, or it’s clogged.

How Do I Make Sure it’s the Catalytic Converter?

The P0420 code is commonly caused by an issue with the converter. But since other faults can trigger it, another way to make sure is by testing the backpressure. To do this, you will need a backpressure test kit or a manometer. They should be no more than $50 to purchase. Or again, you can borrow them from someone you know who owns one. Once you have the test kit, here’s how to do a backpressure test:

  1. If your engine has a secondary air injection system, disconnect the check valve and install the test gauge.
  2. Turn on the car and let it idle. Backpressure can vary between cars depending on their make and model, but most cars should have 1.5PSI at most.
  3. Try revving the car to 2,000 RPM, the gauge should remain at or below 3 PSI. If it fluctuates or is above 3 PSI, then that’s back pressure building up and you may have a catalytic converter issue.

Here’s a video that might help you to do a backpressure test:

How to Unblock a Catalytic Converter

So, now that we’ve determined that there’s a problem with your catalytic converter, let’s discuss how to unblock a catalytic converter. If your catalytic converter is blocked, that means it’s very dirty and you will need to clean it. There are two ways of doing this:

Cleaning without Removing

Catalytic Converter Cleaner - Cataclean Review

The first method on how to unblock a catalytic converter is by using a cleaner such as Cataclean or Liqui Moly. They should cost no more than $15 a can, and you will need around 300ml – 450ml. Also, make sure they are compatible with both petrol and diesel engines, as some cleaners may be specific to one type of engine.

Afterward, make sure you only have 1/4 of a full tank, then simply pour in a can of cleaner to the gas tank. Once done, turn on your car and drive for around 10 – 15 minutes. If the clog in your catalytic converter isn’t too bad, then this method should work. However, if your check engine light was on, then you will need to reset the OBD to clear the error codes. To do this, simply follow steps one through three on our guide to using an OBD scanner, then clear the error codes. This will then reset the check engine light and it will disappear.

As mentioned, if the clog isn’t too bad, this method should work. And once the check engine light has been reset and disappear, it shouldn’t return. If the check engine light returns, then you will need to remove the catalytic converter and manually wash it.

Removing and Washing the Catalytic Converter

The second method on how to unblock a catalytic converter is by cleaning it manually. Before you remove the catalytic converter, make sure the engine is cool. If you’ve just driven it, wait for about 1 – 2 hours for the exhaust system to cool down. Next, make sure you’re working on a level surface and the parking brake is on before you proceed. Afterward, if you feel like you need to then jack the car and put it on jack stands if you need more room to work.

Next, get under your car and remove the bolts that are holding your catalytic converter. Once removed, check for signs of physical damage and check the passageways of the converter to see the blockage. If it’s fully blocked, then ideally you should replace it altogether. Also, try shaking the converter and see if it makes a loud rattling noise. If it does, again, you should replace it with a new one.

If it’s only partially blocked, then soak the converter in a mixture of degreaser and hot water. Leave the catalytic converter in a container for 45 minutes, and check from time to time if the blockage has been cleared. Once done, make sure it’s completely dry before you put it back on your car.

Once you have reinstalled the converter, take your car for a drive and see if there are still any symptoms. And again, if you have a check engine light, reset the light and see if it returns. If it doesn’t, then the method has worked. If you don’t feel like doing this yourself, some auto shops may provide a catalytic converter cleaning service, but it can cost you anywhere between $200 – $300.

Catalytic Converter Replacement Cost

Okay, so let’s say you’ve done both methods on how to unblock a catalytic converter we mentioned above, but you’re still noticing symptoms. And maybe the check engine light returns, what should you do? Well, first, we recommend checking again and making sure the problem is with the catalytic converter. If you’re convinced that the catalytic converter is the issue, and the cleaning methods haven’t worked, then you may need to replace the catalytic converter.

A catalytic converter costs around $600 – $800 for the part itself. As for the labor, the repair shop will usually charge anywhere between $70 – $130 per hour. The time it takes to replace a catalytic converter will depend on the complexity of your car’s exhaust system. On average, the total cost to replace a catalytic converter is around $950.

Needless to say, luxury and exotic cars will cost more and you might pay upwards of $2,500 for a replacement job. A catalytic converter for a 2010 Mercedes S-Class for example is around $1,200 for the part itself. So yes, if you need a replacement, be prepared for a hefty bill.

How to Reduce Catalytic Converter Replacement Cost?

Well, you can always do it yourself and it can save you anywhere between $200 – $300 of labor cost. While it’s not the easiest replacement job, you won’t need specialized tools to do this. A car jack, the correct sockets & wrenches, and you can do it yourself. We recommend checking your owner’s manual first to make sure you have the correct tools.

Also, some cars may have a welded catalytic converter, in which case you will need to saw it off. We don’t recommend you doing this as it can be quite dangerous without proper tools and training. If this is the case, you will need to bite the bullet and pay a professional to do it. If not, then follow these ste

  1. Jack up your car and put it on a jack stand to give your more room to work. Make sure you’re working on a level surface and your parking brake is on.
  2. Undo the bolts of the oxygen sensor (O2 sensor) and remove them before removing the catalytic converter.
  3. Loosen and remove the bolts of the catalytic converter. This might be a bit difficult as the bolts may have corroded, in which case you will need a penetrating liquid, like the WD-40.
  4. Once you remove the bolt, you can then remove the old catalytic converter.
  5. Install the new catalytic converter for your car. Make sure it’s the correct converter for your car, as an incorrect one can cause damage.
  6. Afterward, make sure to tighten up all the bolts and reinstall the oxygen sensor. You can then start the car and see if there are any issues.

We found a guide from Scotty Kilmer on Youtube that might help you with this replacement process:

Selling or Scrapping Your Car

If you still feel that the replacement cost is still too high even if you do it yourself, then the next option is to sell your car as-is or scrapping it. A car with a bad catalytic converter isn’t necessarily dangerous and you can still drive them. But it can cause more damage to your engine over time, and it isn’t very nice to drive either since the engine can misfire it uses more fuel. You can remove the converters and drive without it, but that will result in a loud rumbling sound as you drive along that neither you nor your neighbors will appreciate. Not to mention it’s illegal to remove your catalytic converter.

So, if you don’t want to replace the converter, then it may be time to get rid of your old car and get a new one. If you feel that the cost is too high or it’s too close to your car’s resale value, then you might just want to get rid of it altogether. Keep in mind selling your car as-is means you will have to sell it under market value.

Maintaining Catalytic Converters

So, now let’s say you’ve replaced your car’s catalytic converters or you’ve got a new car. How to maintain the converters so that you won’t have to deal with another expensive catalytic converter replacement? Well, there are some tips to maintain your catalytic converter:

  • Make sure you’re burning the correct fuel-to-air mixture. If the mixture is too rich (too much fuel), it may burn the catalytic converter and cause damage. A lean mixture (less fuel) can also make the catalytic converter burn too hot. Most cars are programmed to run the correct mixture from the factory. If there’s an issue, there should be a check engine light. All the more reason not to ignore that amber light.
  • Drive carefully. The catalytic converter is often not protected by the car’s underfloor, so you might want to watch out. Road debris and bumps may damage your catalytic converter, especially if your car has a low-hanging exhaust. A bad enough physical damage can break your catalytic converter.
  • Use a catalytic converter cleaner. There are debates on how often you should use a cleaner for your car. But we recommend about four times a year should be enough to keep your catalytic converter in good shape.
  • Pay attention to smoke coming out of your car’s exhaust. If you have a petrol car, it should produce clear and odorless smoke. If produces white, blue, or black smoke, then you have a major problem with your engine that you will need to attend to. Leaving this unfixed will cause damage to your catalytic converters.


Great! Now you know how to unblock a catalytic converter. Most catalytic converters can last for up to 10 years, and they can easily last longer than that if you take proper care of your car. If they do become clogged, check just how badly clogged it is. If it’s only partially clogged, then you can either use a cleaner or wash it yourself. However, if it’s fully blocked or you see any signs of damage, then it’s highly advisable to replace the entire unit.

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