Catalytic Converter: Avoid Unnecessary Repairs and Save Your Money

Updated on October 4, 2017
Glenn Stok profile image

Glenn Stok is skilled at researching, analyzing and evaluating technological products and has a knack for clearly explaining their features.

Your check engine light is on. Your mechanic told you that you need a new catalytic converter and it will cost you $800.

Even worse, you need to have an annual inspection soon and your vehicle won’t pass unless you get your catalytic converter repaired.

What the mechanic is not telling you is that it might just be a malfunctioning sensor, or the catalytic converter may be full of crud. It’s not that they are lying to you. They just really don’t know.

Most people think the only way to know for sure is to replace the catalytic converter, reset the check engine light, and see if it comes back on.

A few of my friends already had this experience and I wish they came to me first. I found an alternate solution that worked twice for me already, and it worked for a few friends who listened to me.

This Is What I Did When It Happened to Me

When my check engine light came on, I read the Onboard Diagnostics (OBD) trouble code that’s stored in my car’s computer. I used an OBD diagnostic scanner that I bought on Amazon. You can get one for under $20. It works with all cars sold since 1996. Since then, all cars had to be OBD-II compliant.


The scanner has an LCD display that clearly shows the trouble code and indicates which device is malfunctioning in your car. Some mechanics charge you just to do the same thing, and you’re still no better off.

I feel like it’s a no-brainer to be able to read my car’s computer diagnostic trouble codes by myself, so I know for sure what’s going on.

What Is the Catalytic Converter?

The Catalytic Converter is in the line of the exhaust between the engine and the muffler. Its purpose is to reduce emissions from the exhaust with an efficiency level required by each State to control pollution.

The check engine light will come on if it’s below this threshold, determined by oxygen sensors before and after the converter.

PO420 Diagnostic code

Catalyst System Efficiency Below Threshold (Bank 1)

The Infamous Trouble Code P0420

OBD Code P0420 means the catalyst system efficiency is below the threshold. It‘s a generic code—meaning that it applies to all models of vehicles built since 1996.

This is the most common problem that makes the check engine light appear, although there are other problems that can occur. Each one has it’s own unique OBD trouble code. However, I’m going to tell you about an easy method of solving the problem, that you should try first, when your catalyst system is the culprit.

When a mechanic sees P0420 he or she will tell you that you need a new catalytic converter. This trouble code appears when the unit can’t sufficiently reduce the carbon emissions from the exhaust. However, a catalytic converter does not normally wear out. There is usually some other reason for their failure.

If you spend $800 or more to replace the catalytic converter, you may discover the check engine light coming on again later.

Some mechanics will tell you to try replacing the oxygen sensors first, to see if that solves the problem. There are two of them, one before and one after the catalytic converter. This is necessary in order to properly detect catalyst efficiency.

A good mechanic might also do proper testing by using a scope to diagnose the oxygen sensors, or do a vacuum test or backpressure test, and just charge you a fee for the diagnostic service so that you can decide what you want to do as far as repairs are concerned.

So what do you do? Do you order numerous tests? Do you spend less money first for new sensors? Then if that wasn’t the problem, do you spend more money later on a new catalytic converter?

I Have a Better Method

There is also the possibility that the catalytic converter’s efficiency is simply compromised with oil deposits or other contamination, or just plain gunk from the years of exhaust passing through it.

I found that there is an easy method to clean it out, after which it registers good catalyst system efficiency again. However, my method only works if the catalytic converter is malfunctioning due to contamination as I just indicated.

So how do you clean it out? Easy. High-octane gas can blow out the contaminants. When you’re down to almost an empty tank, fill up a full tank with high-octane gasoline—the highest grade available. Don’t fill up if you have a lot of gas in your tank. This will dilute the high-octane gas and my trick won’t work. You only need to do this once.

Drive until you’ve used up half the tank. When I did it, I just did my usual driving. In a couple of weeks I used up half the tank. There’s no rush, no need to drive endlessly in one session. You’ve got time, don’t you?

After you’ve driven with high-octane for a couple of hundred miles, shut off the check engine light with the diagnostic scanner like the one I use.

Now, continue driving as usual for a week. Watch to see if the check engine light stays off. If it continues to stay off, you’ll know it was only a contaminated catalyst system. The high-octane gas actually cleaned it out.

As I mentioned, I’ve done this twice already. The first time lasted several years. When it happened again, I filled up with high-octane and the problem was once again resolved. I passed inspection and the light never came back on, even long after that.

Is this legal?

You’re not doing anything to fool the system when you bring in your car for a state inspection. So why would this be illegal? You simply blasted out the contamination and helped your car’s catalyst system perform to required specs again.

What If It Doesn’t Work?

If the light eventually comes back on, then you have a more serious problem and you might need that expensive replacement. However, there are still other less-costly causes for a trouble code P0420. Such as:

  • Failing oxygen sensor (remember that’s still a possibility).
  • Damaged wiring of the oxygen sensor connections.
  • Leaking exhaust system (exhaust manifold or muffler).

At least you’ll know for sure that you ruled out contamination, which I found to be quite common among my friends who saved money by following my method.

If you do end up getting a new catalytic converter, make sure you get one that meets your States requirements, or else you may find the check engine light coming on again. The safest thing is to get an original manufacturer brand, or one that is legal for all 50 states.

What Next, If You’re Going for a State Inspection?

After you reset the check engine light with the diagnostic scanner, the car’s computer will indicate a “Not ready” status until you’ve driven a while. This usually resets after 50 to 100 miles.

If you go for the inspection before the system indicates “Ready” you will fail the inspection. Before the inspection, attach your code scanner and check the status. Yes, it does that too. You’ll save yourself a trip.

Stay in the Know With the Same Diagnostic Scanner I Use

Professional U480 CAN OBD2 OBD II Car Diagnostic Scanner Engine Code Reader Tool
Professional U480 CAN OBD2 OBD II Car Diagnostic Scanner Engine Code Reader Tool

Now that you have your own diagnostic scanner such as this one that I use, you can always check your emission system’s status yourself. No need to pay a mechanic for a needless reading. Never get sucked into a repair job you may not need.

The way I look at it, this is a small price to pay to be able to do your own review of what's going on with your car. Having a good mechanic you trust is still important, but it's nice to have the ability to know what happening and to do something about it before spending a lot of money.


© 2017 Glenn Stok


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    • Nell Rose profile image

      Nell Rose 2 months ago from England

      Yes my brother said the same! All the cars are sealed in now! long time gone is when you could tie a pair of tights round the watsit! LOL!

    • Glenn Stok profile image

      Glenn Stok 2 months ago from Long Island, NY

      Nell, You're probably better off that you don’t drive. These days cars require a whole different type of maintenance. When I was young, I used to take care of oil changes and other things myself. There was always room to work. Now I can’t even squeeze my hands in far enough to change a dead headlight bulb.

    • Nell Rose profile image

      Nell Rose 2 months ago from England

      Very useful and helpful, and something I know nothing about and as I don't drive I can't really comment. But this will be really useful for someone who has that dreaded 'need a new one' syndrome.

    • MsDora profile image

      Dora Weithers 2 months ago from The Caribbean

      Very helpful, useful information, although I would engage someone else to help me follow the instructions. Thank you.

    • FlourishAnyway profile image

      FlourishAnyway 2 months ago from USA

      Extremely useful information, Glenn! Thank you!

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