Catalytic Converter: Avoid Unnecessary Repairs and Save Your Money

Updated on January 19, 2019
Glenn Stok profile image

Due to his engineering background, Glenn Stok is skilled at solving technological problems, which has helped him save money on car repairs.

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.

Source

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.

 

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 do not have any engine light or "Service Engine Soon" light on my car but the mechanic is telling me that CAT reading on the diagnostic tool is saying not ready. All test parameters for smog test are already passed except for the CAT reading. What is the problem?

    If you recently reset your check engine light or if you disconnected your battery, then the status of various sensors will indicate "not ready". You have to wait until the ready status occurs. See the section "What Next, If You’re Going for a State Inspection?" in my article for full details.

  • Will the check engine light (service engine soon) go off after the high octane remedy without the diagnostic tool?

    The "service engine" light is not the same as the "check engine light."

    The former is just a reminder that turns on every so many miles, based on the manufacturer's guidelines.

    The latter is the one that warns you of malfunctioning emissions efficiency. This light does go off by itself, but only after a very long period when it detects no further errors from sensors. This does not provide a guarantee that it won't turn on again, especially if the situation is erratic.

    If the high octane remedy that I discuss in the article works with clearing the catalytic converter, then the sensors will stop sending an error code to the computer. However, as I said, this takes a lot of time.

    You'll be waiting for the light to go off, and this may take weeks or months. It's best to turn it off with the diagnostic tool and monitor the status for a "ready" condition before you bring the car in for an inspection.

  • I have a 2006 Subaru Outback. The P0420 sensor has gone on and off for about two years. My mechanic said not to worry. Now I hear the rattle indicative of catalytic converter issue. Is it too late to try the high octane gas method you mentioned?

    The rattle you mentioned indicates that something might be loose. That might also be a result of a badly damaged catalytic converter that definitely needs to be replaced. So you should have your mechanic put your car on the lift and eyeball the situation.

    If you’re lucky, something else is rattling. If that’s the case, then I would say you should try the high octane fix, especially since you say your check engine light has been on and off for two years. That would indicate that the unit just needs a good cleaning that a tank full of high octane would do. But first get that rattle checked out.

  • My Catalytic Converter was plugged up and was so hot that it turned red. This caused the engine to shut down. I cut the converter off and now the engine won't start. Any suggestions?

    You should never have removed the Catalytic Converter. It is there to control emissions pollution.

    Tamperiing in such as way as you did can cause the engine to malfunction and maybe even fail to start. This is because the engine modifies the air/fuel mixture based on data received from the oxygen sensors that are before and after the Catalytic Converter.

    In addition, you will now be registering an error code that will prevent you from passing your State’s emissions test.

    If you followed my suggestion before you removed it, by using high octane gas for one tankful as I explain in my article, you might have been able to clean out the plugged up converter. But since you removed it, it’s too late for that now. You need to have a new Catalytic Converter installed.

  • My Chevy S10 V6 4.3L is a 1991 model. Is there a diagnostic tool for this year?

    Since your car is a 1991 model, it may use the original OBD-1, which began being used on most vehicles in the US in the late 70s. You will need to check your vehicle’s owners manual to see if it is one of those.

    You can also look for the 12-Pin OBD-1 port that was usually under the hood. OBD-2, which began in 1996, uses a 16-Pin port located under the dash.

    If your vehicle uses OBD-1, then you’ll have to purchase a diagnostic tool with a 12-Pin connector that is designed to read those older codes. You also need to buy an extension cord so you can sit in the drivers seat to carry out the required tests while reading the diagnostic tool.

    A dual OBD-1/OBD-2 tool that includes everything you need, including the extension cord for the older models that have the port under the hood, can be found here: https://amzn.to/2M3muA5

© 2017 Glenn Stok

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    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      6 days ago from Long Island, NY

      S-parent 86 - It’s true that you needed to get the sensor replaced due to the P0341 code. But your more serious problem, causing the car to die, still needs to be found by a good mechanic. It’s most likely not related to an emissions problem.

    • profile image

      S-parent 86 

      6 days ago

      I know this is bad but i have a 2003 Honda Accord ex 2.4L. Ive been driving it for about 2 years with the check engine light on. A few months back it started dying when it got warmed up at stop lights or anytime i would slow down or turn corners. I would have 2 push in the clutch and keep revving it up. 1 place said it was my timing belt and they said the belt alone was $106 through them. Of course i didn't buy it cause i know my car doesn't have a belt. Took it 2 a different auto car place they read me off the code. P0341. I also have 2 OBD readers and both confirmed it was P0341. I replaced the Camshaft Position Sensor, Bank 1. It got worse, then just died while driving and its been sitting ever since. Why would 3 OBD readers say the same thing and replacing the part make it worse and die?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      4 weeks ago from Long Island, NY

      Amanda M - It’s definitely worth a try before you spend more money.

    • profile image

      Amanda M 

      4 weeks ago

      Hello! I drive a 2006 Dodge Avenger. My engine light was on and off for a couple weeks then stayed on long enough that I took the car in to get checked. $111 for a diagnostic and they told me it was the code for the oxygen sensor/catalytic converter. On their advise, I had the oxygen sensor replaced first. It cost me hundreds! The light came back on a week later and has stayed on for three days now. Does this sound like a good candidate for your high octane gas trick?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      6 weeks ago from Long Island, NY

      Joseph K - Other things can cause the P0420 error. You could have an exhaust leak. Check for damaged exhaust pipes. Or you might have damaged wiring or connectors to the O2 sensors.

    • profile image

      Joseph k 

      6 weeks ago

      I have this 2001 toyota camry with 2.2 le troubled code P0420.I installed 3 catalytic converters but P0420 will not disappear.All O2 sensors are new,new egr valve and new vacuum modulator.VSV valve is also new.Whats going on here,can somebody help,will appreciate.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 weeks ago from Long Island, NY

      Maria - Same answer I just gave to Aimee Guidry below.

    • profile image

      Maria 

      7 weeks ago

      Hi,

      Toyota Camry hybrid 213000 miles engine light showed on, got checked was code P0420 after 2 days turned off it self with out doing anything, do I still have to get fix or wait until light shows again, please what is you recommendation?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 weeks ago from Long Island, NY

      Aimee Guidry - The fact that your light keeps going off, then on again, indicates the possibility that you only have an intermittent problem. That could be faulty O2 sensors, or it could be the wiring. Those are much cheaper to repair than getting a new catalytic converter.

    • profile image

      Aimee Guidry 

      7 weeks ago

      Hi. My check engine light came on. We tested it with a scanner. My mechanic told me I needed to change the cat converter (bank 1). I read that the o2 sensors have the same code. Do I guess which one it is? Also, the check engine light comes on, goes off, them comes back on. Thanks!

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 weeks ago from Long Island, NY

      Indra Fauzi - If your light keeps coming back on, that is an indicator that you do have a problem that needs to be fixed.

    • profile image

      Indra Fauzi 

      7 weeks ago

      Hey Glenn, I have a 2006 Cryssler Pasifica and i'm getting the P0420 code. I already used your method to fill the gas with high octane for 3 times. My car no loss of power, no strange odors, or any rattle noises. When i disconnecting the battery the engine light comes off. But, unfortunately The engine light comes on again. What do you recommend with this case?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      2 months ago from Long Island, NY

      Carla - You’re asking the wrong question. I think you are being taken advantage of. You said you were told it “could be” the catalytic converter. I would not trust those words. It either is, or it isn't.

      If you want to know for sure, you should get your own diagnostic scanner, such as the one I mentioned, and check the diagnostic code your car is reporting. Paying under $40 for your own scanner is a lot cheaper than $1000 for a replacement you may not need.

      Besides, I never heard of a bad catalytic converter keeping the car from going over 10 mph. As for the noise, it might just be a hole in the muffler.

      Once you rule out the catalytic converter with your own scanner, go find an honest repair shop to figure out why you can’t go over 10 mph.

      Let me know the results. Good luck with it.

    • profile image

      Carla 

      2 months ago

      My car started making a loud noise and I couldn't go over 10 miles. Was told it could be the catalytic converter. Is this hard to fix? Can it be done in 1 day? Thanks!

    • profile image

      Dipen 

      2 months ago

      Thanks, Glen. I am going to have the dealership run the diagnostic test this time. I hope nothing major comes out of it. Thank you again for your response.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      2 months ago from Long Island, NY

      Dipen - It sounds like you never needed a new catalytic converter. That usually is the case when people continue to have problems afterwards.

      Since you had all the related parts replaced and still have the problem, it might be faulty wiring.

      You need to have your mechanic perform a through test to locate the true problem. Maybe find another mechanic you can trust, one who won't sell you unnecessary work. Good luck with that.

    • profile image

      Dipen 

      2 months ago

      Glenn, the code that I am getting is P0138 - O2 Sensor High Voltage Bank 1 Sensor 2. I am not sure what can be done to fix this. My car is Honda Accord 2006. The initial code I got was P0420 which led me to replace both the catalytic converter and the oxygen sensors. One of the sensors turn out to be faulty and gave the code P0139 so my mechanic swapped it with another new one. Now after about 4 days the light came back on with the code P0138. Please help!

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      2 months ago from Long Island, NY

      Dipen - Check the diagnostic code with a scanner as I suggested. That will tell you why the light is on.

    • profile image

      Dipen 

      2 months ago

      I got both the oxygen sensors as well as the catalytic converter replaced but the check engine light came back on after 4 days of driving. What do you recommend in this case?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      2 months ago from Long Island, NY

      Tyler Dunlap - The fact that your light keeps resetting and then coming back on indicates you have an intermittent problem. It might be a failing O2 sensor. However, the actual cause of the problem can only be determined by a mechanic who can check your vehicle.

    • profile image

      Tyler Dunlap 

      2 months ago

      Hey Glenn, I have a 2007 Suzuki Grand Vitara and i'm of course getting the imfamous P0420 code. Now i do a lot of highway driving, roughly 1500 miles a month unfortunately. Now i have no loss of power, no strange odors, or any rattle noises. The engine light comes on and off roughly every 100-200 miles i drive. It doesn't return until roughly 3-4 days after it turned off. Now i'm assuming it's probably a bad O2 sensor and just wanted your opinion on my situation. I'm going to try your method with the higher octane gas later once my tank is low on fuel to properly test this method.

    • profile image

      Thank you! 

      2 months ago

      I’m in the middle of trying your method with using the high octane gas and turning off the check engine light after half the tank has been used. I’ve gone about 50 miles so far and no light yet. Fingers crossed that I’m in the clear because inspection is next month and a new cat converter will cost me $1100.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      2 months ago from Long Island, NY

      tcysimon10 - Since your light went off by itself, you might just have an intermittent problem. Possibly with one of the O2 sensors. I would hold off on the expensive replacement of the catalytic converter since the light went off on its own. If it comes back on, you could try the O2 replacements first.

    • profile image

      tcysimon10 

      2 months ago

      Hi Glenn, my 2006 Sienna engine light came on last month, OBD scanner displayed P0430 (catalytic converter bank 2). I did try using a full tank of high 91 octane gas but the engine light came on last week again with the same issue. TOYOTA mechanic did a diagnostic test, recommended to replace the converter. However, the engine light came off this morning, should I go to replace it because I have make an appointment to replace it next week. If the O2 sensor fails, will the OBD scanner indicates it is the converter problem still ? Should I replace the O2 sensor first, thanks.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      3 months ago from Long Island, NY

      Pchangel - OBD Trouble Codes will always give you a clue of what’s wrong. The P0094 code you mentioned means you have a small leak in the fuel system. You were lucky to get the inspection before the slow leak got worse. But the inspection did not cause it. The car probably always had a small leak. You will need to get that fixed.

    • Pchangel profile image

      Pchangel 

      3 months ago

      Hi Glen - we recently bought a 2014 Buick Encore out of state (TN) -we live in GA. Vehicle had not been inspected because the town driven/sold in doesn't require emission inspections. When purchasing car, finance clerk tells us we will need to get vehicle inspected to get our tag in GA. We drove approximately 200 miles home and before going to get emission test . The next day after returning home I get vehicle inspected and it passed emission test. A few hours later the check engine light comes on. I thought maybe technician didn't properly hook something back up at emission test so went back to testing site. He hooked it up to code reader and first it said it wasn't reading anything and then it read bad catalytic converter - levels low. He reset the check engine light, said it could just be a fluke and told me to watch to see if it came back on. About five days later check engine light comes back on. I then took it to local auto parts store to check code and it's the same code again for bad catalytic converter. P094

      The car of course being a 2014 was bought as is. It's a great car besides for this issue, it's like a brand new car inside and out, runs great. I'm going to try your Method with the high octane gas but I just was wondering if anything during the testing could have caused this light to trigger? The tech said no, but after driving it so far with no problems and the light coming on soon after being tested, it just seemed very odd.

      Thanks for your input!

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      3 months ago from Long Island, NY

      Tom McCullough - You do have to drive a good distance before the computer resets the “ready condition” after shutting off the light. And yes, disconnecting the battery will cause the light to reset. But after the computer detects the problem is still there, the light will come back on.

      The Sea Foam additive is an engine cleaner. But if that didn’t work, then the method I described is worth a try before spending money on a repair.

      Remember that you will need to reset the light and then drive a distance for the computer to detect the status. But driving 110-115 mph, as you said, is ridiculous and dangerous. Whatever you read that suggested that should not have taken seriously.

    • profile image

      Tom McCullough 

      4 months ago

      I have a 2011 QX56 with 61K miles and the dreaded service engine soon came on. Autozone said it was the catalytic converter code left side. I read on another post to add two cans of Seafoam to the tank when it's half full. Then "drive it like I stole it" for a while. I drove 85 miles last night and was driving excessively fast....like up to 110-115 mph. I'm still alive and my engine light is still on. I will try the other tricks like running the tank to E then filling up with high octane. Will the light automatically go out or is that something I would have to reset? Would disconnecting the battery and reconnecting make the light go out?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      4 months ago from Long Island, NY

      Sara S Mccroskey - Since you had recent work done, replacing the Catalytic Converter, you may have an opening in the intermediate pipe leading to the muffler if it wasn't done well. It may have been rusted and overlooked by the mechanic when replacing the Cat Converter. That would cause the same noise as a hole in the muffler.

      If the light is still coming on, it’s possible that your sensors may have been bad instead of the Cat Converter.

    • profile image

      Sara S Mccroskey 

      4 months ago

      Unfortunately, i didn't see this until I replaced my CAT. I have a Jeep Wrangler 2008. Now today driving into work, it sounds like my muffler is bad. It doesn't happen in 1st gear at all, only 2-6. My check engine light goes on then off right away. Any suggestions as to what is making that loud noise, or why my check engine light keeps going off. Thank you so much for any help.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      4 months ago from Long Island, NY

      Cinndy55 - At this point you’ll never know if you really needed the replacement. It’s too late to try my method.

    • profile image

      Cinndy55 

      4 months ago

      Well, I got the P0430 code and I was charged more than the $800. Another shop told me it was my Bank 2, 02 sensor downstream, passenger side on my 02 Nissan Pathfinder converter but the shop doing the repairs said Bank 2 is the engine side. So, they did the repairs but I'm still having a slight jerk in 1st gear. My brother said its the 02 sensor on the passenger side Bank 2 just as the other shop stated. Did I, a 63 year old female got ripped off! Thanks

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      4 months ago from Long Island, NY

      Jennifer - If the light keeps coming back on with code P0420 after the O2 sensors were replaced, then it’s probably the catalytic converter. But make sure your mechanic confirms it’s not bad connections for the sensors, or burned wires.

    • profile image

      Jennifer 

      4 months ago

      Well hello again. So I did the high octane gas thing...used full tank in 2 days... light still on, but more importantly, still having that jerky hesitation feeling when accelerating. Code is P0420.... has been the same code the last 3 or 4 times its come on. Replaced both o2 sensors and 1 catalytic converter. Mechanic reset me after last viist with no findings of any problems... but if course a few days later, light is back on, same code. One interesting thing, I didnt have the jerky hesitation thing until the light came back on a few days ago (about 1 week after last mechanic visit). 2015 Chevy cruze 2lt. 123k miles

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      5 months ago from Long Island, NY

      Jennifer - It’s impossible to say without knowing the kind of car you have or what the codes are that your getting.

    • profile image

      Jennifer 

      5 months ago

      Thanks Glenn, i will try! I did replace both o2 sensors but I think my mechanic mentioned possibly having 2 catalytic converters...? I only replaced one so far. But if the other was bad, when they tested o2 sensors would those numbers have read accurate?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      5 months ago from Long Island, NY

      Jennifer - There are two O2 sensors. One before and one after. It could be the other one that's bad, or it could be the catalytic converter itself. Try my method first.

    • profile image

      Jennifer 

      5 months ago

      2015 Chevy cruze 2LT... I've had the o2 sensors replaced, then the catalytic converter (is there more than 1? I think my mechanic mentioned we're only replcing 1 to start?) Anyway the light keeps coming back on, mechanic ran tests and said o2 sensors and cat are reading accurately, reset the code, and a few days later its back on (I drive a good 700 miles per week). I do notice a rough idle at times and a slight hesitation when stepping on the gas. Ive also used a $30 recommended cat cleaner from the auto parts store. Any suggestions? Should i just try the high octane gas thing? Would that help with the rough idle and hesitation though?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      5 months ago from Long Island, NY

      Laura Homsey - Thank you for posting that feedback on the results of using my method.

    • profile image

      Laura Homsey 

      5 months ago

      Glenn! Because of your article we saved $1,500! We were told by a garage that our cat converter needed replacing, but something told me there was something else to try. Luckily I found your page, and diligently followed your advice. Today we ended up passing our State Inspection with flying colors. I'm also happy to have a diagnostic code reader now to do my own research when problems arise. Can't express how grateful we are to you, thanks again!

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      6 months ago from Long Island, NY

      Stephanie - That all depends on what is causing the reading. The issue could simply be that the sensors are faulty, and that will give the same code as if the catalytic converter was bad. That's why you need to have an honest mechanic review it.

      But if you are told you need a new unit, try my method first. It saved me the cost of having any work done and it worked for several of my friends already too.

    • profile image

      Stephanie 

      6 months ago

      If my car already failed inspection bc of the engine light on bc of catalyc converter will this device still help or do i now have to get my car actually fixed?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      6 months ago from Long Island, NY

      Rob, Octane does have a higher combustion level. That is, it ignites at a higher temperature. You are absolutely correct.

    • profile image

      Rob 

      6 months ago

      Glenn,

      Above, in the Q and A section, you told someone with a question that running high octane fuel will damage their engine because it can cause premature detonation. Octane is a rating of resistance to detonate and the higher the octane, the higher the resistance to detonation, the exact opposite of what you said. This is why higher octane fuel is recommended (if not required) in vehicles with turbos, superchargers or high compression heads or pistons. This leads me to believe the rest of what you have written is BS, as well.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 months ago from Long Island, NY

      Leroy polczynski - It looks like you were screwed. Do you know for a fact that they actually installed a new catalytic converter? In addition, a reputable mechanic would know if the new sensors they installed were compatible. You need to go to a reputable mechanic to have it checked out. There is no way to do that remotely, which would only be guess work.

    • profile image

      Leroy polczynski 

      7 months ago

      Had a problem with o2sensors. Found out the aftermarket and factory don't like each other. Dealer changed them out now have the infamous cat code,p0240! Could this just be because o2s weren't talking to each other. Replaced cat last year with a whole new exhaust system

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 months ago from Long Island, NY

      Diosa1202 - Did you try my method first? That may help clean it out and avoid having to replace it.

    • profile image

      Diosa1202 

      7 months ago

      I had an O2 sensor reading and my mechanic changed the sensor 2x but it keeps getting the check engine light come back. Now he is telling me i need to change the converter. I feel that he hasn’t run enough tests to know this is what it needs for sure. I drive a 2006 Jeep Liberty. What are your thoughts?

    • profile image

      Stephanie Gordon 

      7 months ago

      Thanks for your speedy reply. My upstream O2 sensor is new. I haven't gotten an error message for the downstream one yet. I might try the engine cleaner since it costs less than a tank of high octane gas. I am trying everything I can before replacing the catalytic converter, since it is so expensive.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 months ago from Long Island, NY

      Stephanie Gordon - Since it stayed off until you filled up again, assuming you went back to the usual lower octane gas, maybe you just need to run it longer with high octane. You could always try cleaner, but the high octane does the same thing.

      If the light continues to come back on with the error code, then you might have faulty sensors. Or worse, it actually could be that the catalytic converter needs to be replaced.

    • profile image

      Stephanie Gordon 

      7 months ago

      I followed your suggestion and ran a full tank of high octane gas in my car. The light stayed off until I filled up with gas again, and then the PO420 error message came up. Would you recommend an engine or catalytic converter cleaner as a next step? Maybe #1 and 2 fuel injectors are dirty and causing the reading. Further suggestions will be appreciated very much. Thank you.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      7 months ago from Long Island, NY

      Stephanie Gordon - You may as well wait to see how it is after your trip with the high octane gas. If the light stays off after that, then you’ll know it was not either of the O2 sensors. Please post your results here. Have a good and safe trip.

    • profile image

      Stephanie Gordon 

      7 months ago

      I have a 2002 Toyota Camry with 317,000 miles on it. I have recently gotten a P0420 error message. The dealer in my area told me to replace my catalytic converter. I have already replaced the spark plugs, # 3 and #4 fuel injectors, and the O2 sensor-upstream. I have done all of this work myself, as I am retired and trying to save on car repair bills. I am going to try running a tank of high octane gas through my car next week on my drive from VA to GA. I hope this will do the trick. Do you recommend replacing the downstream O2 sensor as well? My car is running fine after it warms up for a few minutes. Thank you so much for your informative articles and advice.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      8 months ago from Long Island, NY

      KayRhea - It has nothing to do with driving over 50 miles. That is only necessary to get all the signals to reach “ready” state after the light has already been turned off, as I explained in this article. Since your light is still on, the mechanic didn’t fix the problem. You need to go back and get them to do the job right.

      Did you get your own code reader, such as the one I mentioned? That is the only way you’ll know what the computer is complaining about, and then you’ll know what to expect the mechanic to be correcting.

    • profile image

      KayRhea 

      8 months ago

      I just had my catalytic converter put on my 2013 Ford Focus SE and the check engine light is on. Would it have to do with me not driving my 50-100 miles?

      I have had to replace fuel pump.. O2 sensors and vapor canister. I have no idea what more it could mean and I spending way too much for the check engine light to keep coming on. PLEASE HELP

    • profile image

      Jhope 

      8 months ago

      Its works people! My engine light came on, autoshop said it would cost 3k to replace the “cats”. I didnt get the device Glenn described, but my light went off on its own with the high octane gas like Glenn described. I could only find 91 premium gas, so still worked. I have a 2002 4runner. Thank you Glenn!

    • profile image

      cingram 

      9 months ago

      Thank you for offering this helpful information. My Camry has a P0420 code set though the MIL (or check engine light) is NOT on. I'm going to try your method and see what happens. Thanks again. You provided a useful possible solution as well as quite a bit of other useful information.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      9 months ago from Long Island, NY

      Natalie RG - The dealer who sold you that car lied to you. Never trust buying a car when the check engine light is on. It will never pass inspection. It's too late since you already make the purchase.

      Your only option is to sue the dealer if you want to go that route. But if you don't have the paperwork to prove the condition upon purchase, you're out of luck.

    • profile image

      Natalie RG 

      9 months ago

      My 2008 Ford Expedition is giving OBD 304, 308, and 420. The dealer says that I failed to maintain the catalytic converter plugs which led to raw fuel dumping into it. Well, the check engine light has been on since I bought it and they explicitly told us that it was just an error with the o2 sensor and we shouldn't worry about it as everything was working fine. We've stayed up on all of our maintenance, but the warranty won't cover it because they are saying it's our fault and we should have brought it in sooner. I brought it in as soon as the vehicle's performance changed.

      What do you recommend?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      9 months ago from Long Island, NY

      Quentin R. - Thanks for confirming that my method worked for you. You sure kept excellent records as proof!

    • profile image

      Quentin R. 

      9 months ago

      Great article! I followed everything the article suggested after failing emissions with trouble codes P0420 & P0430 on 12/4/18 at 15:19:16 but 20 days later I went back for a retest on 12/24/18 at 14:29:26 and got the paper in my hand signed with the overall results: PASS. I also, before and after pictures of the results, just in case you were as skeptical as I was.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      10 months ago from Long Island, NY

      Carlosbell - That has nothing to do with the Catalytic Converter. Your check engine light would be on if you have any emissions issues, in which case you can read the OBD code to see what it is.

    • profile image

      Carlosbell 

      10 months ago

      Hi Glenn,

      Wish I would have seen this article before now.

      So my 2006 Nissan Altima is having issues accelerating. While parked, if I push the gas pedal to the floor, it will barely its 2x rpms.

      Was wondering if you believe that to be a catalytic converter that needs to be cleaned or replaced.

      Thanks in advance

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      10 months ago from Long Island, NY

      Mozee - You should report that machanic for fooling you. It’s illigal in any state to charge for a new one and then just clean the old one. You need to check with Toyota about your question if there is more than one. In any case, try my method before spending any more money.

    • profile image

      mozee 

      10 months ago

      I had a catalytic converter replaced on my 09 Toyota Sienna. I explicitly told the mechanic I wanted a new converter installed which he agreed to. After 11 months , the engine light reappeared and the mechanic says the other converter has gone bad and needed to be replaced. My instincts told me to get a 2nd opinion and I went to another mechanic recommended by Emissions. He took pictures of my converter and it showed instead of replacing the converter, with a new one, they merely cleaned it and welded the pipes. I was told this is illegal in the state of MD. Presently I can't afford to have it replaced since I have just paid out a lot of money. My question is are there multiple catalytic converters on my van, and could the welding that was done cause the other to go bad?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      10 months ago from Long Island, NY

      Danielle - The deceased gas mileage has nothing to do with the catalytic converter. You might have other problems developing.

      Remember to try my method if the light does come back on before you spend money on a new one.

    • profile image

      Danielle 

      10 months ago

      I have a 2005 Nissan Altima. My check engine light came on, took it to my mechanic and he says my catalytic coverter needs to be replaced. He just doesn’t know how long I have. So he cleared the check engine light and said to wait and see if comes back on. If it comes back on in a day or two that means it needs to be replaced right away. If it doesn’t come back on that means I have a while. It hasn’t come back on and that was a month ago. Meanwhile my gas mileage is decreasing. And I’ve noticed I have less power while accelerating than I did a few months ago. Does that mean he’s right?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      11 months ago from Long Island, NY

      Erik, The fact is that my car is 20 years old and the method of using high octane gas has helped my avoid getting a new catalytic converter. Say what you want, but my experience, and that of the those who tried my method, speaks otherwise.

      I'm sure it doesn’t help is all cases, but it has worked so far. My light came on a few times in the past ten years with a P0420 code, and this method helped keep it clear for a couple of years each time.

    • profile image

      Erik 

      11 months ago

      This sounds like a sales pitch for a code reader. How would this method work for cars that are already running premium gas?

      When catalytic converters first hit the threshold of setting a catalyst efficiency code, the codes can be cleared and it will often take a long time before the code resets. This isnt because you "cleaned it out" with overpriced gasoline. It stays off because the cat wasnt that bad yet. Catalytic converters should be properly diagnosed using proper methods which involves more than a code reader.

      Also, catalytic converters are only designed to last about 10 years. 10 years is a lot longer than the average american keeps a new car. At 10 years, the cat can just be worn out.

      99% of the time a P0420 sets, the catalytic converter is the problem.

      Sorry, Glenn. Your "technical background" does not make you an expert in catalytic converter diagnosis.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      13 months ago from Long Island, NY

      Chris, since you already have a new catalytic converter installed, then the method I described will not work. It’s already a clean unit, assuming the shop put a new one in.

      Since your check engine light came back on, that means it was not the catalytic converter causing the error. Do you know the error code the machanic read? It’s useful to have your own code scanner such as the one I mentioned.

    • profile image

      Chris 

      13 months ago

      Just had my cat replaced and engine light came back on, can I still use your method to fix it?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      13 months ago from Long Island, NY

      Jeff Barge - All auto repair shops have diagnostic scanners. If your machanic is just guessing or not telling you the code, you’re going to the wrong one.

    • profile image

      Jeff Barge 

      13 months ago

      Why doesn't the law require auto repairers to buy this device instead of makng expensive replacemenets?

    • profile image

      Jamie 

      22 months ago

      Still working my way through the tank of premium gas. I filled it all the way up (tank capacity is 12.3 gallons, I put in 12.16 gallons). Hoping that it will clean whatever was causing the light to go off out. As I mentioned, my light was going on and off for about a hundred miles and was off prior to me filling the tank with high 91 octane fuel. The light has not come on again.

    • profile image

      Jamie 

      22 months ago

      Glenn, thanks for clarifying. It's for a 2008 Civic Hybrid that has always been carefully maintained. I'll stick with the 91 and report back.

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      22 months ago from Long Island, NY

      Jamie - Too high might blow the engine if it's not designed for racing. Use just all 91. It worked for me. Just don't dilute it. Fill on a close-to-empty tank.

    • profile image

      Jamie 

      22 months ago

      Glenn, thank you for your response! I am going to be trying your method. I've got a P0420 code that has been going on and off (now it's off) for the past two days. There is a Union 76 near me that has 101 octane racing fuel. I was thinking of getting about 9 gallons of 91 and then 1 gallon of the racing fuel. Would that be okay or should I just stick with ALL 91?

    • Glenn Stok profile imageAUTHOR

      Glenn Stok 

      22 months ago from Long Island, NY

      Jamie - I was referring to the highest octane you can get in your area. That varies. Typically in the U.S. octane ratings can be as high as 91–94 for premium gasoline.

    • profile image

      Jamie 

      22 months ago

      How high is high octane? Are you saying something like 101? Or 91?

    • Nell Rose profile image

      Nell Rose 

      2 years 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 imageAUTHOR

      Glenn Stok 

      2 years 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 years 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 years 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 years ago from USA

      Extremely useful information, Glenn! Thank you!

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