Question about 2001 Toyota Corolla

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P0420 code on Toyota Corolla

Erik,

I have to say, you sound like one of the honest mechanics out there and I have a question. I have a 2001 Toyota Corolla with 143,000 miles on it and I have a problem with this stupid P0420 code and I am ready to dig a hole and drive the car in!! This code started last year. I brought it to a shop and I had the code diagnosed and was told it was the converter. I had my boyfriend change the converter since it was a hell of a lot cheaper than the shop. It fixed the problem for the emissions test and eureka, the light came back on about 3 months ago. We went ahead and changed out the whole exhaust system under the car (converter, pipes, O2 sensors, muffler) and the code went away. Now the code is back on and we just can't figure it out. The car is running fine and like you stated in the last thread, the code is a f***in pain to look at. Do you have any idea what else it could be? An experts opinion is what I am looking for. Thank you!

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  • ginapace Sep 27, 2008

    Erik,



    I have another problem on my 2001 toyota corolla and I was wondering if you could help me. I refuse to bring the car to the dealership since I know for a fact I will get screwed! Like I stated in the last thread, everything has been replaced as far as the exhaust system goes. I still have the check engine light with a P0420 code for bank 1 and 2 and I do appreciate the advice you gave me on that. I noticed 3 days ago that the car is hesitating when I am at a stoplight once in a while or after I start accelerating after I have been at a stop light. The car is starting fine and my gas mileage is fine. I have a new code that is a P0171 code which states the system is too lean. I have read that it's the MAF and that it should be cleaned. My boyfriend cleaned it last night with electronic cleaner. When he put it back in the car and I started the car and checked the codes on the check engine light, that code went away, which I thought it was fine. I cleared the code last night and I drove it a little today around the neighborhood to test it and the same thing is happening as far as the hesitation goes. The check engine light has not come back on yet. I have ordered a new MAF since I think it is faulty, but I would like your opinion since I respect someone like you and not the crooks at a Toyota dealership that are only in it to make a buck. I want to add that the last 02 sensor that was replaced was the one before the converter closer to the engine and a body shop did this. Ever since they replaced that one, I noticed it was harder to accelerate and then I started getting the hesitation about a few weeks later and then the P0171 code came on. I am thinking of replacing the MAF and also maybe replacing that 02 sensor since it may have been faulty. Sorry I am rambling. Thanks. Any advice is appreciated. Thank you so much.

  • ginapace Sep 27, 2008

    take care and thanks very much again. any other problems with anything else send them my way first, take care have a good night

  • MPAR Oct 01, 2008

    Hi,



    Looks like I have similar problem with my 1999 toyota corolla with 148k miles on it. First time the check engine light came on was 3 years back, I got it diagnosed at Autozone and got general code saying there was some issue with catalytic converter. However the engine light went away in 3-4 days. It came back on last month, and the guy at Autozone diagnosed and said it was catalytic converter error code (it was general code not giving specifics on catalytic converter or oxygen sensor). THe light went away in 3-4 days. Now it's back again and I got it diagnosed and it's the same general code. So first question is how do I get a scan done where I can find out exact source of the problem, i.e. is it the oxygen sensor or catalytic conveter? I called around number of places and their tests will suggest the general code, beyond that they have to manually look for the issue. My last resort will be the dealership as they normally tend to rip off the customers. Can you give me some direction on what or how should I approach this issue?



    Thanks a lot,

    MP

  • tkrauss Nov 18, 2008

    2003 corolla with p0420 code which will not stay reset, even after replacing cat converter twice, #2 oxygen sensor twice.

    is it worthwhile to replace engine oxygen sensor?

    with over 100,000 miles, could muffler be partially blacked and causing over heat in CAT? the muffler guy said it seemed to be running hot.


  • wboyle13 Jan 07, 2009

    I noticed that all of the Corolla posts were from Sep to Dec. I had a problem like this with a Saturn and now with my 2001 Toyota Corolla. It always goes away in the spring, may be due to changes in the fuel for the winter. luckily both cars were inspected in the summer so the check engine light was never a problem for me.

  • TAISIN818 Mar 30, 2009

    My 2001 Corolla (160k miles) failed smog test in california because of P0420 error code. I just bought a universal oxygen sensor (Bosch) and attempted to replace the rear sensor (the one screwed into the exhaust pipe between the tail pipe and the cat. converter) but stopped because i could not see/access/unplug the wires of the sensor. The Bosch universal replacement sensor's instructions say to cut the 4 wires off the current sensor and then reattach them to their respective wires of the new sensor. I am reluctant to snip anything. Please help if possible.

  • amitvar7 Apr 02, 2009

    I have the same exact problem, word by word. I too cleaned the MAF sensors with a electronics cleaner.

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Well thank you very much you have me blushing : ) i went to school for automotive and after seeing people be taken advantage of till it almost made me sick i chose to take my own business path, I might not be the best mech in the biz, but i would like to think im the most honest, i have trouble charging people ive never met before lol and usually give them 1/2 the price a normal shop would with out marking up my parts 50% like most shops also, once again thank you.to explain what is happening, the heated o2 sensor between the engine takes a waveform (voltage reading to determin the air/fuel mixture) then the mixture travels through the cat and is cleaned and comes out to the 2nd post o2 sensor, the computer checks these to make sure they are different and that the cat is doing its job by changine (cleaning) the exhaust flow. the reason you are having this code thrown is because both sensors are reading the same which means that the converter isnt doing its job. now this means that the cat is bad, the heated #2 o2 sensor is defective, or the #2 o2 sensor circut is open/shorted.Tthe answer to your problem to the best of my knowledge would first make sure that is the only code that your car is throwing (to make sure another problem isnt causing this one) if p0420 is the only code showing you will want to check through the entire exhaust from the engine exhaust housing back to make sure you have no exhaust leaks. you may have a p0130 which is the heated o2 in the front or a p0136 which is a problem with the other o2 post cat. these codes should show, if they dont i would still go over the wiring of the sensors from them to the ecu make sure they are not shorted, if you go to a shop with a scan tool they should be able to check the o2's with it and make sure your fuel trims are where they should be also. if only the p0420 i would guess there is a leak somewhere, all the heat cold heat cold back and forth can loosen bolts and strech metal joints in the exhaust system. if that doesnt help please let me know and i will research it more much harder, but this is what the manual for your car says and what i believe also, please let me know and i'll get back to you right away, also make sure the cat didnt just randomly go bad, but dont let them replace stuff say you want it tested and make sure they have the right tools to do it. take care and thanks very much again. any other problems with anything else send them my way first, take care have a good night

Erik
EZ Automotive/U.S. Army

Posted on Sep 19, 2008

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  • erik mcdonald
    erik mcdonald Dec 03, 2008

    if the first sensor reads the same as the one after the cat it sends a code that the cat is not working, because the chemical reaction in the cat that takes place should read different coming out than going in thats what a cat does its uses the chemicals in it to remove NOx and CO and if its not working then both sensors will read the same, saying that the cat is ineffective, get it? i cant believe i got a thanks for trying fing rating when i explained ever single possible solution or problem, never helping that person again

  • erik mcdonald
    erik mcdonald Dec 03, 2008

    if anyone that is not gina wants help contact me from my profile so i get credit and not just comment posts, thank you




  • erik mcdonald
    erik mcdonald Dec 09, 2008

    gina why would you change my rating to inapropriate? i asked others to contact me because this is how the website works, it has nothing to do with you i dont understand, this is your post and only people trying to help you are supose to post, so it doesnt change, ??? im not saying i dont want to help you but just that i dont want to help the other people because this is not their post and its turning into a chain of me repeating myself, please change your rating or contact me personally, i dont understand why you would change this to inaproppriate when i went so far out of my way to help you?

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My name is Brian, i was a Tech at a toyota Dealer for several years and decided to open my own traveling tech business. Ive seen this problem occure quite often and the solution is probably easier than you think. First thing you should do is remove your Mass Air Flow Sensor, By removing the two screws, located on your airbox. Second take a look at it, there is a little filament that reads airflow, it should be orange in color. most times what happenes is, due to age or poor air filter conditions, Crud will aquire on the end that faces the inside of the airbox and turn a blackish film color. this will throw the sensor off thinking its not getting the air its supposed to be, giving false readings. What you can do is take some carb/choke cleaner and spray it down till its orange again, let it sit and dry. install the MAF sensor and reset your light. give it about a week if the light stays off, presto you just saved yourself loads of dough and time. i recently had a customer come to me with this issue saying he took it to the shop and they replaced the O2 sensor and the light came back on a few days later. i stopped by and checked his MAF, it was very very dirty. As i stated earlier i was a Tech at a local toyota dealer and have ran across this many times. The reason it doesnt throw a MAF sensor malfuntion is because it technically is still working. The reading s coming from the dirtyMAF sends the wrong info to the ECU sendign the wrong amount of Fuel/Air to the Engine, causing the code your getting. hopes this helps let me know!

Posted on Oct 14, 2012

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It is a tiny crack in the intake manifold. It causes the car to **** air inside the exhaust system. This makes the ECU send out false codes.

Posted on Dec 09, 2009

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If the error code P0420 is coming up on a reader, and it is based on the 1st sensor being the same as the 2nd one, why would it matter if, say, an exhaust leak occurred in the system somewhere other than between the 2 sensors (the cat)?  I don't understand why an exhaust leak would matter.  Can someone explain?  Where does the electronic data come from if not one of the sensors? Thanks, Scott

Posted on Nov 24, 2008

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My car: 2003 Camry, 4 cylinder 2AZ-FE engine w/California emissions (reside in PA - go figure), 98.5K miles.
Had a Check Engine Light (CEL) occur 3-4 days after an inspection that required a new gas cap (old cap would have failed inspection).
Brought it in to get it checked out for a diagnostic review, same out as code P0420...dealership said bad cat and quoted me $750-$800 to get it fixed that day since it would fail emissions (thank goodness I had passed emissions a few days prior). I told them I wanted to do some research b4 I committed to fixing.
Researched this and other online resources that suggested many others having same error code that went through replacing cat only to discover that did not address issue. I also read that cats should last much longer than my 98.5K miles suggested.
I read many instances that this P0420 code is a finicky readout that Toyota technicians do not have a great deal of success interpreting...many times it falsely indicates an issue where no issue can be found.
I reviewed some home based options to attempt & address CEL. For the 2003, I saw the EFI fuse removal for two minutes...did not work.
The one that worked for me was the removal of the negative battery post fitting...left off five minutes, came back and replaced. The CEL indicator went away and has stayed off for the 1st few days...only negative part of this is resetting clock and radio presets...big deal vs. close to $1K of cat repairs.

Posted on Jun 11, 2010

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I'm tend to agree with Brian (walaxvw) above and add one other trick. The Mass Airflow sensor should be checked especially if you've installed an K&N air filter. The K&N filter uses a spray-on oil that is supposed to trap most dirt. However some of that oil vaporizes and re-collects on anything else in the airflow piping. If you unscrew the MAS sensor and look inside it should not look like fuzzy brown tonsils. They should be either orange or white in color and on my 2000 Tacoma I occasionally spray them down pretty good with an electronics cleaner I buy at my local electronics store. Mine are white. When they look clear I blow them out gently just to remove any excess solvent and re-install. Clear the code and it should work fine.

The other thing I would check, in fact it's why I bought my 2000 Tacoma so cheap is the gas cap. With an after-market gas cap the system pulls the wrong vacuum on the gas tank. That equates to an computer losing it's mind and reporting everything from an EGR, O2 sensor, Catalytic converter bad, etc. I paid the man for the truck drove it to a dealership. Bought a factory made gas cap for that vehicle and since then I've not seen a check-engine light since.

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