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Toyotapro, ASE master tech
Category: Toyota
Satisfied Customers: 9974
Experience:  ASE Certified, 10+ years Lexus and Toyota Certified
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I have a 2002 Toyota Corolla. The check engine light is on ...

Customer Question

I have a 2002 Toyota Corolla. The check engine light is on with, I believe, P0420 check engine code. A mechanic friend reset the CEL, but it returned after 500 miles. I had an emissions test yesterday, which I failed (I was ignorant that the CEL would be an automatic fail). What are my options? Can I have my friend reset the CEL light again (or can I do this myself by disconnecting the battery?) and then retake the test? If not, what should I do? Go to dealer for diagnostics? Replace the sensors, the muffler, the Cat converter? How do I know I can trust the mechanics assessment?
Submitted: 9 years ago.
Category: Toyota
Expert:  Toyotapro replied 9 years ago.
Hello and thank you for using just answer. P0420 means that the catalytic converter is no longer performing properly. It will need to be replaced as long as this is the only code stored, aftermarket converters in my experience are a waste of money on this car and I would highly advise you to use only factory brand parts. If the light was off for 500 miles then either you did not have enough non-stop driving until that point to complete the drive pattern or the converter is marginal on performance. For now what you can do is clear the code again and drive it for about 10 minutes with the speed at 55mph using light acceleration, this should be enough drive time to set all monitors other than converter and EVAP system so that you can pass inspection depending on your states regulations.
Customer: replied 9 years ago.
Reply to Peter's Post: Thank you for your prompt response. Can I reset the converter by disconnecting the battery or do I have to have my mechanic friend do it with the scanner? Also when replacing the cat converter, do you recommend using the Toyota dealer or does it not really matter?

Also, I am looking at teh DEQ report and the only problem it has is MIL: FAIL. I do not know if this is significant to you, but I thought I should give you all the information that I have.
Expert:  Toyotapro replied 9 years ago.
Yes you can reset by unhooking the battery for a few minutes, juse be sure that you have the key out of the ignition. Dealer parts-yes I highly highly recommend them, it does not really mattery who installs them as long as you use a factory part, it is as simple 4 bolt deal to replace this converter. Most states you don't "fail" because of check engine light, rather you are "rejected" because of it. If you need to get this done BEFORE you repair the converter then try the drive cycle I suggested and try to get inspeted again.
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Customer: replied 9 years ago.
Thank you Peter, that was great!
Expert:  Toyotapro replied 9 years ago.
Thank you and let me know if you need any further assistance. Have a good evening and thank you for using just answer.