Question about Toyota Corolla

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My CE light is on. The code is PO420. It is a 2002 Corolla. Smog is due. Two years ago, the same thing happened. I bought a scanner, cleared the light. Took it to smog. Passed. But this year, I cleared the light, it kept. What should I do? Is it true that my car can't get smogged if the light is on? Is it true that even if I had the problem fixed, cleared the light, I can't take the car to smog until the car had gone through 40 start cycles until all the monitors are ready? I have heard that sometimes no matter what you do, the CE lights kept coming back. I would really hate that. Thank you.

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  • Toyota Expert
  • 350 Answers

The P0420 is for the catalyric converter, you'll have to have it replaced. It will fail the test as long as the light is on. Clearing the code information also clears the monitor infor, to pass the monitors required you'll have to put some miles on it in both city and highway driving, not all monitors may be required so check with your local smog station which ones have to pass.

Posted on Apr 15, 2017

  • mechanic144 Apr 15, 2017

    bad catalytic converter is last resort if you ask me. if the car fails its usually for a reason. either with too much gas entering the system due to being run way too rich, or too much air coming into the system due to being running to lean. could also be running the wrong fuel. 1) check spark plugs. check gap with owners manaul or manufacturers specs. also, while spark plugs are out see if there's any fuel on them by smelling. if you smell fuel, this is and indication the injector for that cylinder is being held on for some reason, either leaking or bad driver etc. should still be a tan color. if plugs ok, check air filter. ive seen where a plugged air filter will allow little air to get in causing a rich burn and in couple instances, no starts. also while monitoring sensors with scanner, see operation of oxygen sensors. a bad o2 sensor could also trigger a cat converter code as well. if all is good that way, then you can still see if the converter is bad with the scanner. if you see the post o2 sensor not switching like it should, and pre-cat o2 sensor changing, then its likely, that the cat itself is in fact bad. that should also affect power as in having severe loss of power under load, being hard accel like up a hill, but run good at idle...so there are a few things to consider before condeming the catconverter.

  • theodore ritter
    theodore ritter Apr 16, 2017

    As I stated in my original reply the P0420 is very specific to a catalytic converter inefficiency, no other codes were mentioned, O2 sensors, a/f ratio sensors and lean conditions would show other codes, so looking for other reasons is a waste of time and money, the cat can actually be tested by connecting a diagnostic tool that is capable of running a monitor on the cat's performance

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SOURCE: 2000 corolla with trouble code po420

If the code has cleared on its own then you need to disconnect the battery and re-connect it. This will clear the codes out of the memory. If you don't want to do this you can go to an auto parts strore and have them hook the little computer up to your car and they can clear out the code as well.

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trade it in on the scrappage scheme against a new one .or take it to an authorised garage for emmisions ,cant just point a finger at a certain component and say change that .Sorry but without the right equipment i would only be making educated guesses .What condition is the air filter in ---did you clean it before you went for the test

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