I have a 2003 Corolla CE with 147,000 miles, and I've been driving around with a check engine light for quite some time. It's smog check time for me, and since I live in CA, I need to pass both emissions and OBD-II checks.
The error was diagnosed as P0420, "Catalyst system efficiency below threshold - bank 1", and my mechanic replaced the catalytic converter and cleared the codes. After driving for a bit, the check engine light came back on, and I brought the car back to my mechanic. He tested the O2 sensors, and they were both bad; one was marginal and one was completely broken. So he replaced those and again cleared the codes.
One hundred miles later, the light went on again. Same error code!
I hope the MAF sensor solves your problem. I changed out both O2 sensors and the MAF in my daughter's 03 Corolla last January and she still has a recurrent P0420. I could not smell anything from the exhaust and the voltage signals seems to be normal for a working CAT. At this point I suspect the ECU, but won't be able to look at the car until next month. There is a long thread on this a little farther down the forum page.
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Make sure you use a genuine Toyota replacement catalytic converter. Many of the aftermarket ones are not worth the space they take up.
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I have a 2002 Sienna with the same problem. There is a TSB for this code. There is a programming error in the Engine computer. Toyota has a reprogrammed new computer to fix the issue. My van is at the dealer now to have the ECM replaced for over $1100. that repair is based on Toyota TSB. I hope this fixes the problem, even though it is very expensive considering it is a design flaw!
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I brought the car back into the mechanic, and he took readings from the O2 sensors. They seemed to be wrong, given that the cat and both sensors had just been replaced. Nevertheless, he ordered a replacement sensor for the one providing a bad reading (post-cat, I believe), but it gave the exact same reading.
He then found a TSB regarding just this issue, and brought the car into the dealer to have the computer flashed. The data was cleared after the service, so the CEL went off at that point. I've done a couple drive cycles for a total of about 50 miles so far, and the light isn't back on at this point. I'm going to do a bit more driving before bringing it back in for a smog check. Fingers crossed...
My long P0420 saga is over! Although my cat was bad and needed replacing... and my O2 sensors were also bad and needed replacing... it was ultimately the computer re-flash (per the TSB I mentioned in my last post) which finally put this problem to bed.
Smog check passed. Registration renewal signed, sealed, and delivered.
Can you tell us what the "flash" cost? I plan to get this done for my daughter's car. I think it has the same problem.
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91 Camry auto with 150000+ mi-best car ever
98 Tacoma ex cab 5 spd 1.7 liter with 85000 mi-new
98 Volvo V70 AWD with 140000 mi
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Hi all. Before buy the service technicians story on the cat, check out my story and try the fix. It cost me $8.00 to "legally" turn off the P0420 induced CEL. My03 started pushing the code about a year ago. Got the same response from the techs as you. However, the light went out when I spent a week in Florida last July driving on Florida gasoline. Drove home on FL gas, no light. Fill up with Tennessee gas, CEL is on 16 miles later. It aint the cat, it's the ethanol blended gasoline. I suspect the programming genius did not take into account the possibility of the usage of ethanol blended fuel and thus the P0420. I have Honda throwing same code. I employed this fix on both vehicles and no light.
Go to this link: http://www.honda-tech.com/showthread.php?t=2162522. Follow it exactly and you have a good chance of ridding yourself of the P0420 CEL and saving yourself enough money to go for a nice vacation.
Hi all. Before buy the service technicians story on the cat, check out my story and try the fix. It cost me $8.00 to "legally" turn off the P0420 induced CEL. My03 started pushing the code about a year ago. Got the same response from the techs as you. However, the light went out when I spent a week in Florida last July driving on Florida gasoline. Drove home on FL gas, no light. Fill up with Tennessee gas, CEL is on 16 miles later. It aint the cat, it's the ethanol blended gasoline. I suspect the programming genius did not take into account the possibility of the usage of ethanol blended fuel and thus the P0420. I have Honda throwing same code. I employed this fix on both vehicles and no light.
Go to this link: http://www.honda-tech.com/showthread.php?t=2162522. Follow it exactly and you have a good chance of ridding yourself of the P0420 CEL and saving yourself enough money to go for a nice vacation.
Ethanol blended gas has been out for years, why would your CEL just come on now from it and not years ago? Also I live in Florida and Florida is a Mandatory Ethanol State, so gas here is blended too and is no different then gas up north!
I posted that last May. TN got ethanol blended fuel about 3 years ago and I started having CEL lamp illumination about 1 year later. Instead of arguing with me on this matter, why not spend some time logically explaining why my light went off, stayed off on Florida gasoline. Then came back on 16 miles after a fill up with TN gas? Until you or anyone else can do that to my satisfaction, the gas is a factor in the CEL illumination due to the C0420 code. All this chat is a moot point because the fix is still working to this day. CEL has never come on again.
Instead of arguing with me on this matter, why not spend some time logically explaining why my light went off
I don't call it arguing I call it questioning, some people are followers like sheep and believe anything, I don't...Who knows what caused it to go out, faulty ECM, faulty wires, sensor going bad, bulb burned out, warm Florida air, coincidence, divine intervention or just plain luck, could be a number of things, what I'm trying to say is yours is not a logical explanation especially when Florida gas has ethanol in it just like other states, there's no reason your CEL should have gone out just from using your magical "Florida gas" what worked for you might not work for a thousand other cars! Sorry just my opinion
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Can't fix P0420 error code. Please help!
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