Auxiliary Emissions ControlOBD2 Codes

P0420 – Meaning, Causes, Symptoms, & Fixes

What Does Code P0420 Mean?

  • P0420 definition: Catalyst system efficiency below threshold (Bank 1)
  • Issue Severity: MODERATE – Extended driving with this code can cause internal engine damage.
  • Repair Urgency: Get this code fixed as soon as possible to avoid further damage to your emission system and possible engine damage.
  • Diagnosis: The most common cause of a P0420 is a bad catalytic converter, but it can be caused by anything from a faulty oxygen sensor to a rich or lean running condition, or misfires. Because there are so many variables that could cause this code, the best cost savings is to take your car into a shop to have it diagnosed as quickly and accurately as possible.

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The function of the catalytic converter is to break down harmful pollutants that are created by your vehicle during the combustion cycle and convert them into less harmful gases. Code P0420 indicates that the catalytic converter is not functioning efficiently, therefore increasing the output of harmful pollutants by the vehicle.

P0420 Causes

The most common reason for check engine code P0420 is catalytic converter failure, but there are other potential causes for this code. It’s important to look for other codes that could indicate the root cause of converter failure, such as misfires or an incorrect air-fuel ratio.

  • Worn or internally failing catalytic converter (Most Common)
  • Faulty oxygen sensor
  • Faulty air-fuel sensor
  • A leak in the exhaust system
  • Misfire (the root cause of converter failure)
  • Rich or Lean air-fuel ratio (the root cause of converter failure)
  • Leaded Gasoline (the root cause of converter failure)

P0420 Symptoms

  • Check Engine Light is on
  • Lack of power from the engine
  • Decreased fuel economy
  • Rotten egg or a sulfur smell

How Do I Fix Code P0420?

The first step is to get it diagnosed to figure out what is causing the catalytic converter fault. 

If you’re having catalytic converter issues and you’re not comfortable diagnosing this issue at home, we recommend finding a RepairPal certified shop nearby to pinpoint the problem and give an accurate estimate for repairs. 

These shops can not only help you figure out what’s going wrong before you waste time and money on the wrong parts, but they also offer a minimum 12-month, 12,000-mile warranty and stand behind all their estimates with guaranteed fair pricing.

> Find a RepairPal Certified Shop Near You

How Much Does It Cost to Fix Code P0420?

P0420 can be caused by anything from a bad sensor to a failed catalytic converter. It’s impossible to give an accurate estimate without properly diagnosing the issue first. 

If you take your car to a shop for diagnosis, most shops will start with an hour of “diag time” (the time spent in labor diagnosing your specific issue). Depending on the shop’s labor rate, this typically costs somewhere between $75-$150. Many, if not most, shops will apply this diagnosis fee to any required repairs if you have them perform the repairs for you. From there, a shop will be able to give you an accurate estimate for repairs to fix your P0420 code.

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Possible Repair Costs for P0420

Once properly diagnosed, P0420 may require one or more of the following repairs to resolve the underlying issue. These prices are based on national averages and include parts and labor. Your cost may differ depending on your location and type of vehicle.

DIY Steps to Diagnose Code P0420

If you’d like to try to fix code P0420 at home without throwing money at parts, you’ll want to follow the steps below for proper diagnosis. Keep in mind this is an advanced-level diagnosis and repair and not recommended for beginners. Diagnosis can be a time and labor-intensive process for inexperienced DIYers.

DIY difficulty level: Advanced

This repair requires mechanical knowledge and is not recommended for beginners.

Tools/parts needed (our top picks from Amazon):

STEP 1: USE FIXD TO ENSURE NO OTHER ENGINE CODES ARE PRESENT.

Use FIXD to scan your vehicle to verify P0420 is the only code present. If other codes are present, they must be addressed first.

STEP 2: EXAMINE THE EXHAUST SYSTEM FOR DAMAGE AND LEAKS.

Pay close attention to the exhaust manifold, gaskets, and exhaust pipes pre-catalytic converter. If any leaks are found, repair the leak, clear the code, and complete several drive cycles to verify that was the fix.

STEP 3: CHECK THE DOWNSTREAM O2 SENSOR.

With the vehicle running and at normal operating temperature, use the FIXD live data feature or a digital multimeter to check the voltage reading of the downstream O2 sensor. The downstream O2 sensor produces a relatively steady voltage reading of approximately 0.45V if the catalytic converter is functioning properly. If the voltage of the downstream O2 sensor is constantly jumping between 0.1V and 0.9V, the catalyst is worn and the catalytic converter needs to be replaced.

Common P0420 diagnosis mistakes

Oftentimes, this code is thought to be a faulty O2 sensor or A/F Sensor. While this is a possibility, the most common problem is a faulty catalytic converter. Do not overlook other codes that are paired along with P0420. Codes like P0300, P0301, P0302, P0303, P0304, P0305, P0306, P0307, and P0308 are misfire codes, and these codes require misfire diagnosis. If the catalytic converter is replaced without repairing the misfire, the new catalytic converter will go bad again. Also, make sure you don’t have codes P0174, P0171, P0172, or P0175 which can mean the engine is running rich or lean, which can burn out your catalytic converter. If these codes or any other codes are present, they should be addressed first.

Still Need Help Fixing Code P0420?

If you’ve followed the steps above and are still experiencing check engine code P0420, please contact the FIXD Mechanic Hotline if you’re a FIXD Premium subscriber or find a RepairPal certified shop near you for proper diagnosis and fair pricing.

Justin-Hughes

Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

Justin Hughes
Recovering autocross and track day enthusiast. Once turned a VW Jetta into a pickup truck. Lives in a van down by the river. Dream car: 2001 Subaru WRC rally car.

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    117 Comments

    1. This was very informative!

      1. Bank1, sensor 1 was replaced on the 7th of April. Electronic load detector was replaced about 2 weeks ago. These two things were detected by my cousin’s FIXD device. I did the ELD
        myself a friend with a lift did the sensor.

        1. Hi William! Thank you for sharing your experience with us! We really appreciate the feedback!

          1. I went through a huge puddle of water after that check engine light came on. We tested it and p0420 code came up.we cleared the code no return of check engine light. What was the problem the water shocked the cat and sent a signal? Need an opinion

          2. Live in a cold climate and noticed that when extremely cold that this code comes up. Is there need to worry? It has come on and off.

            1. Not to worry unless the CEL stays On.
              Cold weather brings out the Gremlins in the 1st gen Tacoma, lol
              Everybody has them!

        2. Both my vehicles one a 2003 GMC Envoy SLT and 2009 Nissan Murano SL. Have the infamous P0420 Code.
          I want to know what kind of money iam looking at. To late for the GMC but my recent car that I got on April 16, 2019 two days later the code pops up
          What’s up with that.

          1. The seller probably cleared the code just before the sale, and it took 2 days to reappear.

          2. I had went to put the Catalyst converter so why is it showing up if it was done just my check engine is on that’s what’s the problem yes I like to get it fixed

            1. Can the converter be bad and not have any of the symptoms listed? I’m getting the cose but no issues with rotten egg smell, gas mileage is same as before…etc.

            2. Shannon, if you arent getting the code yet, i strongly suggest adding cataclean or some kind of cleaner, (CRC guarantee too pass is good as well) while you still can. Once it’s completely clogged, the cost can be astronomical. (for my 2011 JEEP LIBERTY its $2400 to replace) and only $200 of that is labor. Some states (NY being one) enforce what’s called the “California emissions” requirement, which means you can only use the converters supplied by the dealer, and designed to pass California emissions.

        3. What is the actual cost of a catalytic converter that the suggested parts and repair is estimated btw $1500 & $2000?

          1. I just did mine, 08 Malibu. Paid $100 for the part on Amazon and $250 to install… Was quoted much higher.

            1. Reason is because this is a general cost if you’re having the garage purchase and install. Also keep in mind that more states are going to California emissions which is quite pricey which is rather inflated pricing and dealer only for emissions parts

          2. I get all my parts from rockauto.com. I only paid not even $280 for bank 1 cat and four 02sensors.

            1. You might also want to look on carparts. Com. Alot of their parts are a little less expensive

          3. Look on card to look for parts

      2. Yes I did know you had trained service professionals who could assist me with advice.

        1. Good morning sir, pls I want know more about the fuel consumption in a particular vehicle what cant be the cause of that after putting all the catalyst and oxygen sensor

          1. Very good information . I’m very grateful .7

        2. Hi,
          I just got my Bank 2 catalytic converter replaced in April so I would pass emissions and now my bank 1 catalytic converter is out? Is that possible? Should I have changed all together if this was going to happen?

          1. How do I find the videos on fixing the car it shows the parts

          2. I always buy my parts and labor is cheep where I’m at in ky it’s 70 to 75 an hour I get most of my parts at carid.com there a great place even have dealer parts also

        3. Awesome tool

        4. Don’t forget to take the old one to the scrap yard to get $50. For the precious metals inside

      3. Where Can you find bank one on the catalysti converter

        1. Where can I find bank 1 on 2003 Honda accord ex

        2. Is it worth it changing the catalytic converter on 2005 Toyota Camry

        3. I have a 2007 Nissan Maxima. I have a p0420 code. I just replaced the bank 1 catalytic converter and both O2 sensors and both Cam shaft position sensors. I thought the problem was fixed but after performing along test drive, I am getting hesitation when I try to accelerate from a dead stop and the code returned along with the check engine light. Once it gets passed 2000 rpm and in second gear it accelerates like normal. This hesitation only seems to be present after the engine warms up. It didn’t happen until the end of a 40 mile test drive at highway speed. Any ideas?

        4. I need some help. I have a 2007 GMC Acadia. The engine light is on with a P0420 code. This is what has been replaced/repaired
          1. Mass airflow sensor
          2. Throttle body
          3. Valve covers/gaskets
          4. 2 upstream O2 sensors & 1 downstream sensor.
          5 . catalytic converter has been replaced twice
          All of this and the light is still on. Can some one please give me some advice on what to do now. I don’t know if it is part of it, but the evap code always comes on & won’t reset. Please help!

          1. Based on the instructions given here, you need to concentrate on that EVAP code before worrying about the P0420 code. This code has shown up on my Envoy and what the EVAP is or what the EVAP problem is -that the only one I haven’t figured out yet concerning this problem.

          2. Evap Code most likely is you need to get a new gas cap. Also, make sure the area around the gas cap is free of rust etc.. Hope this helps, so many times people go through so much when it’s just the gas cap.

          3. Spray some wd40 in the back of the engine while its running. If it starts to die down or shut off, you have a vacuum leak

      4. i have a 2004 Z06 and removed the secondary air pump along with all the tubing which supplies fresh air into the headers for cold starts during only the first 3-4 minutes and after 2 years im guessing the ECM doesnt know its missing cause its been running like new since then with no issues

    2. where is the camshaft position sensor bank 1 located in the 2011 jeep grand cherokee

      1. Hi! It looks like it should be above the water pump and behind the accessory belt. We highly recommend getting a vehicle specific repair manual that provides diagrams of all of this, such as https://www.amazon.com/Jeep-Grand-Cherokee-Gasoline-engines/dp/1620921073/ref=sr_1_1?ie=UTF8&fixd_blog-20&qid=1523413703&sr=8-1&keywords=2011+jeep+grand+cherokee+repair+manual

        1. I changed the crankshaft sensor the catalyst system efficiency below threshold b1 show up the engine light went off. Do I need to change catalyst converted to

    3. I had a new catalytic converter put in the automobile. I have taken it to the garage prior to purchasing the FIXD product. Garage said that the test they ran says their is a short somewhere and that is what is causing the error message. Converter is working fine according to mechanics. To find the short, they said that they would have to test virtually every wire around the engine, and the labor to find the short could cost hundreds of dollars. Rather than pay 100’s of dollars strictly in labor costs, I have chosen to ignore the engine light. Interestingly, after I use the Fixd to diagnose the engine, it then resets the engine light to off. Usually within a short time, or a few miles of driving, the check engine light comes back on. And your recommendation is ?????

      1. Hi Mike! If the car’s engine control module recognizes a fault after the check engine light is reset, it will cause the check engine light to come back on.

        1. How do we fix the engine control module? Mine is doing the same as Mike’s. I have replaced all the sensors and a new catalytic converter.

    4. Thank you this was very helpful understanding how things work.

      1. Hi Leon! Thank you for the feedback, it really means a lot to us!

        1. Thank you for sharing, it was very informative and somewhat a relief from worrying.

      2. I USED A FIXD DIAGNOSTIC READER, AND MOST CODES ARE ACCURATE, I LIKE WORKING ON CARS,,BUT IT WOULD BE NICE AND FIXD WOULD BE MUCH HELPFUL IF IT WOULD SHOW YOU A EASY PICTURE DIAGRAM OF WHERE THE BROKEN PART IS LOCATED,,EXAMPLE : WHERE IS P0420 BANK 1 LOCATED ON YOUR VEHICLE ?

        1. Now that is a great question, Armando

    5. Worked like charm

    6. p1272 code
      replaced the following on a 2005 Altima. both up and downstream sensors, and the exhaust manifold with catylitic coverter also replaced MAF sensor and the fuel pump reset the code day later thecode came back. it said engine running too lean the only thing I didn’t replace is the throttle body
      any suggestion, i

      1. I have a 2005 Nissan Altima with code p1272 . which I’m told is running too lean I replaces the exhaust manifold w/caty convertor. also replaced both up and down stream 02 sensors , MAF sensor and the fuel pump, cleared the codes with FIXD day later same code came back the only thing I didn’t replace is the throttle body fuel has a internal filter. so I thought the fuel pump pressure might be the cause. any suggestions.

        1. Pvc valve replaced?

      2. Hi! Thank you for reaching out. Codes that start with P1 are manufacturer specific. Could you please provide us with your year, make, and model and we will look into it!

      3. Lean means not enough gas in the fuel mixture. Could be fuel pump or fuel filter

    7. Would you happen to know where I can put my multimeter to test the voltage? Is it on the o2 sensor or the connector?

      1. Hi Enrique! You connect the red probe to the signal wire, and the black probe to a ground. We are working on producing how-to’s with this information, but in the meantime, we found this to be very helpful: https://axleaddict.com/auto-repair/How-to-Check-an-Oxygen-Sensor

    8. Manifold leak fixed but light keeps turning on. Not worth $1,500 for new cat. Light stays off sometimes weeks, sometimes less sometimes more.

      1. Try a local muffler shop. Mine had generic (universal?) catalytic converter for about $300, installed.

    9. I have a 2002 PT Cruiser getting this error. It has only one oxygen sensor an it is upstream of the converter. How do I voltage test the O2 sensor (BTW I replaced the sensor and I still get the error).

    10. Used a gas treatment, light out after 16 gal. Time will tell if this fixes the problem
      .

      1. Good luck, Glenn! Please let us know if it does!

    11. I have FIXD and I got P0420 with Check engine light, VSC and Trac Off lights on the dash board. What is the relationship between P0420 and the VSC and Trac off? why are all three warning lights come on. I reset them with my FIXD, the lights go away but they appear after less than 100 miles. I noticed also when I turn teh ignition key on without starting the car, there is a hissing and clicking sound coming from behind the brake reservoir. How do all these problems combine to give this P0420?

      1. Hello Emilio! We are sorry about the troubles you are having with your vehicle. I passed this along to our team and they said they would go through the diagnosis for P0420, fix it, and then see if the the VSC/Trac Off lights go off.

      2. Hi Emilio,

        Our team did some more research and found that if your catalytic converter is severely clogged, it could restrict the exhaust which would impact the calculation of engine load, thus causing the VSC and Trac Off systems to stop working. Please let us know if this helps!

      3. So I’m not sure what’s going on with mine, it’s the same code but for some reason my check engine light will turn off by itself but then a few weeks later it comes back on with the same code. The oxygen sensor has been replaced twice, I have no leaks, the only thing I haven’t done is replace the catalytic converter itself, but I checked the downstream o2 sensor and it’s reading 0.45v it’s just driving me nuts that the light won’t stay off

    12. I replaced the engine in my 95 Ford Mustang. With the higher compression from the engine pushing out old carbon build up, I received this fault code.. 1 can of Sea Foam cleared it up. I had to reset the computer 4 times.. thanks to Fixd.. quick and easy to do.. car is running like a champ.

      1. Hi Frank, thanks for sharing your success with us! That is awesome!

    13. I have a 2002 PT Cruiser, there is only 1 O2 sensor and I have changed it to no avail. Any suggestions on what to try and/or how to diagnose the issue?

      1. Hi Bob,

        Check to make sure that the readings with your multimeter are correct. This will verify that your catalytic converter is functioning properly. If this does not fix the issue, contact our Mechanic Hotline to gain more insight!

    14. I recently purchased a used 2008 Saturn Vue and my check engine light is on and showing code P0420 catalystic system failure because of an exhaust leak, where would I find my exhaust and what am I looking for? ( I am a young female and know nothing about cars )

      1. Hi!

        You will have to reference your car specific service manual to locate your exhaust and other car parts located under the hood.

        The FIXD Team

    15. Thanks. I understand the code much better now.

      1. I just replaced both 02 sensors in 2002 Yukon XL 1500 car seem like it was fixed then it shutoff same issue persists what else could it be ?

    16. I have replaced the catalytic converter twice and still have the same problem

      1. Hi Carlos,

        The catalytic converter is only one of the things that could be problematic in trouble code P0420. Please do not overlook other tests and possible errors that it could be!

        Thank you,
        The FIXD Team

    17. Hello! My check engine light (solid) and cruise control (blinking). FIXD code detected was P0442 – Evaporative emission control system leak. I had FIXD clear the code prior to taking my 2005 Subaru Forester to a mechanic. The engine light and cruise control lights went out. Today a week later, the lights are back on. I used FIXD and Code P0420 – Catalyst System Efficiency was detected. I’m assuming that by not addressing PO442 code it lead to Code P0420?

      1. I have a 2009 Suzuki SX4 with a code P0420 and I am trying to figure out which one to change can you help me please

        1. I want to find out if it is bank 1 or 2 censor up stream or down stream

    18. Oi Bom dia estou com o cod P0420 ativo na minha XC60 2011 e tambem esta ativo o cod P0171.
      Alguma dica.

    19. I put my Bank 1 Sensor 1 O2 sensor on yesterday and today engine light came back on and I did a reading and it say P0420 catalyst system efficiency below threshold bank 1. Can anyone tell me what it could be

    20. Would a modified exhaust system cause a P0420 Code? For example a “Cat-less” Exhaust System that is not OEM but all direct bolt on (no welding).
      This is for a 2000 Subaru Impreza 2.5RS – Manual. Exhaust System: Spec-D Headers (Heat Wrapped), Stromung Catalytic Eliminator Front Pipe with Bosch Upstream and Downstream O2 Sensors, Borla Intermediate Pipe and Muffler. All installed on 3/18 including Gaskets.
      The reason I ask this question is because with this type of Exhaust System, I am getting that code P0420. All brand new parts, all installed at the same time, all with new gaskets, and with the bolts torqued to spec. So that would eliminate “leaks” as the cause. The O2 sensors were also installed at the same time. So that would eliminate “bad O2 sensors” as the cause. Now for the Catalytic Converter…there is really none to speak of because of the Stromung Catalytic Eliminator Front Pipe 1999-2005 Impreza Non Turbo I also installed at the same time. It is a direct bolt on replacement piping, specifically designed to replace the catalytic converter. Were I live there is no emission’s restrictions/requirements and I mainly use it for off road use (track car).

      So is that the reason why I am getting that code? The only other thing I can think of is the wiring because of the year and age. Any ideas would be greatly appreciated and thank you for reading my novel 😉

      1. I don’t know if you ever solved this issue, but for you and all our readers,; you have to keep in mind that without a cat, you’ll get basically the same signals as the upstream sensors. The computer sees this as a failed cat and sets a P0420 code. What the computer wants to see is an almost steady signal of around 0.45 volts. While some computers can be ‘fooled’, most are set up to set an error code if you attempt to circumvent the downstream sensor. Doesn’t hurt to try!! Good luck.

    21. Where would the catalytic converter bank 1 be on a 2006 Chrysler Sebring convertible?

    22. where is the downstream O2 sensor located in the 2007 Honda Accord. I need to measure
      the voltage reading of the downstream O2 sensor.

      1. The downstream O2 sensor should be located post-catalytic converter.

    23. My catalytic converter pass state inspection but it’s say p0420 bank 1 because of it my service light won’t turn off I also been told that my service light and check engine light are different

      1. Hey Jeffry! The check engine light typically means there is something wrong with your vehicle, while the service light can simply mean it is time to have your car serviced (i.e. get oil changed or rotate tires).

        FIXD Team

    24. Would you recommend trying a catalytic converter fuel and exhaust system cleaner to address a P0420 fault? If so, what is a good product/brand to use?

    25. When I scan the 2005 GMC Safari, with “live gauges”, the #2 and #5 O2 sensors (One is upstream, the other down) are jumping all over the place and it sets a ‘420’ code about once every 2 or 3 weeks. Bad O2 sensor? A weak spark plug? Thoughts?

    26. I have a 2006 VW Jetta 2.5L with CEL on. The code is P0420. I did a temp reading at Cat Converter. The exhaust side is 150+ higher in temp. There are no other codes attached. Any Idea?

    27. For this code p0420 if I wanna fix it, by priority, which one should we fix and replace: oxygen sensor or whole cat?

    28. Witch side is bank 1 on a Nissan Extera

    29. I have a 2007 Nissan Xterra, only code it’s showing is P0420 catalyst system efficiency below threshold bank 1. Did some research and some people are saying it’s the catalytic converter is bad. Any ideas?

    30. I have a 08 Chevy Silverado v8 I have 4 O2 sensors which one would be Bank #1 if someone could help me out with this question be much appreciated. Thanks

      1. Bank 1 is drivers side. Upstream is before the catalytic converter. Downstream is after the catalytic converter. Bank 2 is passenger side. Upstream is before the catalytic converter. Downstream is after the catalytic converter.

    31. I replaced the upstream O2 sensor on my 2010 Chevy Aveo, but still have the CEL and P0420. Would not replacing the downstream cause this?

      1. Possibly. It’s also as likely that you simply have a bad distributor cap, or a coil pack that’s got a weak output. Even a spark plug that’s worn can cause this code. Many times you can see it on the “Live Data” of the fix’d app. This is especially true if it happens most often after driving in the rain. Moisture can get into the distributor or the coil pack and cause an erratic spark or signal. Check those! Loose exhaust connections can be tricky to find, but at idle often sound like a chick- chick- chick- sound. The reason for this isn’t that the exhaust comes out, but that between each cylinder’s individual exhaust there’s a slight vacuum created that draws in air and throws all the readings off, causing the computer to set the code.

        1. Wow that is great. I had a P0300 P0301 P0304 all mis fire. Then driving in rain threw P0420. So just what you said. So what is it just coil pack? I just bought new plugs and coils. So what is it?

    32. Have P0430 and the car with skid marks warning. I just took my SUV out of shop to get rebuilt transmission. Could these warnings have anything to do with rebuilt transmission?

    33. My FIXD is showing a problem with the catalytic converter (Bank 1). At the dealership they verified the issue. However I got that converter replaced last October at a garage in my town. I cleared the check engine light and 3 days later it came back on. Guess I have to take it back to the garage where I had it worked on last year. SIGH!!!

    34. FYI, never had an error code before until I added a fuel treatment from Lucas. The engine ran fine, no problems until the engine light came on sometime after adding the treatment. Cleared the code and it has not come back since, but I haven’t added anymore fuel treatment either. The fuel treatment has not made any of my other cars engine lights come on, just my GMC Sierra 1500.

      1. You didn’t say which code you got, what year, or how much mileage. It’s possible that the treatment dislodged some gum- AKA “crud” that deposited itself on a spark plug or the O² sensor. Many times this deposit will burn off and not be a problem afterwards.

        1. My 2003 Chevy Avalanche is throwing both P0420 and P0430. With the advanced troubleshooting on the FIXD it is telling me that the evap system is failing. I have replaced the vent valve and the purge valve and the gas cap. What should I look at next?

    35. Does anyone know of code P420 on a Tacoma can be fixed with gas cap replacement?

    36. I found the info quite useful but would like to explore much more.

    37. code p0420 Three months ago light came on and i replaced the o2 sensor and light went off for 3 months. It has now come back on with the same p0420 code. I did not replace the a-f sensor where is it located and what are my options?

    38. I had the P0420 code pop up a while ago. I changed the downstream O2 sensor, which didn’t solve my issue. A few days ago I changed the bank 1 catalytic converter. When I turned the car on and ran a scan the P0420 code along with 5 out of 6 cylinders showing a misfire. I also saw the sensor needed calibration, which I did. The misfires didn’t return but after I cleared the P0420 code it returned a couple days later. I guess my next moves are to change the upstream O2 sensor and/or checking the new catalytic converter for a leak because it was a pain in the neck to install.

    39. Has your AC has been recharged in the last 24 hours? Is so you may get one P0420 on the next startup. The gas is heavier than air, gets sucked into the intake manifold .. and fools the O2 sensor into believing the catalyst has failed.
      Reset the MIL and the problem will not recur.

    40. You should have been resetting the check engine light while making those repairs, but if you didn’t, go ahead and reset it with a FIXD Sensor or by disconnecting the car battery for about 10 minutes and then run the car for 50 to 100 miles. If the light comes back, check your codes again, if it doesn’t come back, the problem is fixed and your scanner should read Ready.

    41. I have a subaru forester 2007 non turbo that has a CEL for P0420 (bank 1). I’ve used a OBDII scanner, and it shows that the short term fuel and long term fuel trim in bank 1 are ok, but shows a result of 0 for bank 2. Is it possible that the downstream sensor is at fault? Even when the OBDII scanner says bank 1?

    42. Can a P0420 (bank 1) be caused by the downstream 02 sensor (bank 2), or is it only for upstream (bank 1)?

    43. You are an awesome tribute

    44. 2014 Chevy Cruze p0420 code keeps coming back on I just had catytic converter put on. 02 sensor are good so what bow

    45. 2013 Chevy Equinox FWD. Just drove 1300 miles from Cal to Washington . Vehicle has 78,000 miles on it. Running fine, no issues great gas mileage 28-30 mpg. Car had California Smog test about 4 months ago and tested fine. Today while driving check engine light popped on, no other indication of any problems. Pulled over, and ran a FIXD diagnosis and P0420 was code. No suffer smell or rough running. Checked gas cap and it was not fully to lock (clicked) position. Secured it and reset engine light and so far it has not returned. Could not having gas cap secure account for this reading or do I need to go to the dealer. Catalytic Converter is supposed to be covered repair under warranty for 100K as I recollect will check manual in the AM before going to dealer if light comes on again.. If I keep driving for awhile with no other symptoms and check engine light does not return am I likely in the clear? I seem to recall that if gas cap not secure that can effect emissions.

    46. Can a bad catalytic converter after having put a hole in it to unblock it cause your air conditioner to turn off while driving the car ? Then after shutting the car off for while and starting the car again the air conditioner will work again.

    47. Check the coils. I have an ’06 Dodge Dakota that was getting P0420 codes. I found the spring inside the #1 coil had disintegrated, causing a weak spark and a rich fuel mixture in that cylinder.

    48. I have replaced both o2 censors on my 02 Camry no check engine light is on but still telling me that it is the problem don’t know what to do

    49. I have a 2012 chevy cruze 1.8 eco. That i just put a new to me motor in bc it got hot smoked the head gasket and threw the timing belt in all one fluid motion while driving 65 down the interstate. Now that motor didn’t have a P0420 code but about a month later after having the motor replaced the CEL came one, just hoping it wasn’t the same PVC issue I had with the old motor which it wasn’t. Car ran fine even with the light until 2 nights ago I was taking this older gentleman home from our work. And about 15 mins into my drive mind you im doing the speed limit of 55 when it starts bucking I back off the throttle get back into and something. Kicked in neutral and coasted for a lil while, started the car back up and no issues until I’m on my way home my car won’t let me go faster that 45. But my wife gets in it to go to work yesterday and has no problems what so ever. She drops the car back off with me at work and I take her home which was a 10pm now when I got off work about 7 hours later. The car did its cold start revs, but once it kicked down to normal running rpm which is and 700 to 800 rpms. Now it fluctuating in between 500 and 700 and when it does I can feel it in the driver seat pulsating. When I go to slowly Rev the car you can literally feel it almost acting like it’s killing a cylinder but you get past 2k without a load just fine luckily I only had to drive a few blocks but it was bucking and jerking in the same fashion it was 2 days ago. Got it home let I idle for a lil bit and then the intermitten(almost like the car has a big vacuum leak again) jumps and skips. Shut the car off for maybe 10 seconds started it back up and no hesitate jump or miss. Ik I’m not going to leave it at that. And as I still on a ish ton on this car I am not able to just get out from underneath and not to mention it has became my wife’s daily. And being from Southern illinois I’m not exactly made of money as it took my 2 months to save enough to pay 1500 for a motor and someone to put it in. I’m having these same issues and she’s wanting to go to Kentucky today with the car. Also I just had the oil changed 3 days ago if that means anything. And I always get gas and the same station in the same town. About to call my local muffler shop and see if they can just put a new exhaust resignator and cats on it. And then go from there bc even though it’s located literally right on the side of the motor I honestly don’t feel like dropping more money into. It’s a 2012 chevy cruze 1.8L Eco body has 157xxx on it and the motor has 145xxx on it now. Now I’m no Aaron Kaufman or anything but I’m no average Joe when it comes to mechanical work. And they fact that you need and sensor for a sensor so this relay to can tell this fuse to go f off. Is insane and absolutely mind blowing. Why can’t we go back to mechanical fuel pumps, distributors or even a 750cfm double pump quardrajet holley carb for crying out loud. Well I’m just a 31 yr old man rambling now. But would sure appreciate some feed back on this as to I need to start planning my attack for the day being as the wife wants to be on the road by 10

    50. I have a 2013 Chevy Cruze. Code P0420. None of the symptoms nor engine light. My coolant keeps disappearing. Idk where it’s going.
      Some days it’s a rough idle when first turned on, assuming it’s starter… What do you think? Replaced thermostat, water pump, and radiator..

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