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ptlamb

Catalyst Efficiency Low

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I have a 2003 corolla ,140,000mi, at 123000 check engine light came on and went off after a few hundred miles.( I was on A long trip)Thought it was a dealer plug. it came on again right after 130.000( 2 weeks after inspection,New Jersey,strict emissions testing) 1st mechanic said replace cat, 2nd said clear it out see what happens.now at 139000 it came on again,cleared it out 7 days ago, came on again. I detect a sluggishness in cars accelaration. code was PO#420 catalyst efficiency low bank #1..Any suggestions about approaching this problem?

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That particular code - P0420 - can mean many things. Anything from a faulty downstream O2 sensor (sensor after the catalyst), to some damage in the exhaust system (blockage, crack, bad seal somewhere), to bad ignition timing, to a bad catalyst. Normally, this code pops up when the rear O2 sensor gets confused.

 

Usual fix is to reset it and see if it comes back - if it does, then more diagnostics need to be done. The fact that you can actually "feel" sluggishness in the performance may mean that the timing is off (could be a bad plug to a bad ECM) or the catalyst is truely clogged up. With the amount of miles on the clock - and depending on the history of the car and its maintenance, could very well be a bad catalytic converter. So far you have done all the right steps - reset the code and wait and see if it comes back. Now that it is back - you have to diagnosis it a bit further to narrow down the issue. Ex. Does the acceleration sag at low RPMs or higher RPMs? Does it sag at a certain point or over a certain RPM range? Notice any change in fuel economy, smoke on startup, etc.? Did they run the car on a dyno for the emissions testing or just the OBD-II readiness check (some places do both tests)? If they did do both tests - what were the numbers for HC, CO, CO2, and NOx?

 

I've had cats go as early as 40K miles (completely slagged over - bad O2 sensor + constant misfires/bad timing) and as long as almost 200K miles (and still counting). I've got about 137K miles on my Corolla and so far so good - but I will not be surprised to see a cat replacement in the near future.

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I've had cats go as early as 40K miles (completely slagged over - bad O2 sensor + constant misfires/bad timing) and as long as almost 200K miles (and still counting). I've got about 137K miles on my Corolla and so far so good - but I will not be surprised to see a cat replacement in the near future.

 

 

I just had a smog test and barely passed (113 out of 120 on HC, and 49 over 20 on CO); I thought it was because I accidentally switched to 91 octane and my car was running rough, but now I'm wondering if it could be the catalytic converter. My car (1988 Corolla SR5) has 195K miles with the original cat. Unfortunately, my ECU has not told me anything. In fact, the check engine light has NEVER come in all the years I've owned it, except on start-up. I have heard that you can knock on the cat (after letting it cool down!) and if it sounds hollow, then you've lost your catalysts. Is this true?

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I've had cats go as early as 40K miles (completely slagged over - bad O2 sensor + constant misfires/bad timing) and as long as almost 200K miles (and still counting). I've got about 137K miles on my Corolla and so far so good - but I will not be surprised to see a cat replacement in the near future.

 

 

I just had a smog test and barely passed (113 out of 120 on HC, and 49 over 20 on CO); I thought it was because I accidentally switched to 91 octane and my car was running rough, but now I'm wondering if it could be the catalytic converter. My car (1988 Corolla SR5) has 195K miles with the original cat. Unfortunately, my ECU has not told me anything. In fact, the check engine light has NEVER come in all the years I've owned it, except on start-up. I have heard that you can knock on the cat (after letting it cool down!) and if it sounds hollow, then you've lost your catalysts. Is this true?

you'd have to have a shop test the cat for you, not all shops have the machine and most wont bother to do it since its just as easy to replace it as it is to test it. odds are your cat wont pass the next test and that your cat is almost worn out.

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You'd have to have a shop test the cat for you, not all shops have the machine and most wont bother to do it since its just as easy to replace it as it is to test it. odds are your cat wont pass the next test and that your cat is almost worn out.

 

Thanks. This makes some sense. 2 years ago, my HC and CO figures were half of what they were this past week, and 2 years before that, they were half that. So my current HC and CO figures are 4 times those of my 2003 smog test. I thought that maybe I needed a tune-up, but I am now looking into getting a new cat, after a thorough tune-up of course. I just picked up new spark plugs. Time to get out the timing light . . .

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You'd have to have a shop test the cat for you, not all shops have the machine and most wont bother to do it since its just as easy to replace it as it is to test it. odds are your cat wont pass the next test and that your cat is almost worn out.

 

Thanks. This makes some sense. 2 years ago, my HC and CO figures were half of what they were this past week, and 2 years before that, they were half that. So my current HC and CO figures are 4 times those of my 2003 smog test. I thought that maybe I needed a tune-up, but I am now looking into getting a new cat, after a thorough tune-up of course. I just picked up new spark plugs. Time to get out the timing light . . .

With the car just barely passing smog, it is a good sign that a tune-up will help, but you probably need a new converter.

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Im fixing to have to get my o2 sensors and cat conv scanned too. Mileage has gone to crap from 30mpg to 27mpg a month ago, and now down to 24mpg. Im at 86k with new iridium plugs properly gapped, recharged air filter, cleaned maf, and new pcv yet still have crap mileage. Hoping its a o2 sensor and not the cat. I'll find out next week.

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Im fixing to have to get my o2 sensors and cat conv scanned too. Mileage has gone to crap from 30mpg to 27mpg a month ago, and now down to 24mpg. Im at 86k with new iridium plugs properly gapped, recharged air filter, cleaned maf, and new pcv yet still have crap mileage. Hoping its a o2 sensor and not the cat. I'll find out next week.

Do you have the CEL on??

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No CEL for me. I forgot to add in my last post that I run it on chevron techron 87 octane and I also seafoam the crankcase and gas tank every now and then to where the engine and oil look clean so the injectors should be clean also, plus the 7yr old plugs with 85k miles on them were quite clean for their age when I took them out. Along with scanning for a lazy o2 sensor I'll get a vacuum guage and see if the cat or exhaust are plugged or constricted.

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I looked around the auto shops and no one has a scan tool that will read the o2 PID's. Theirs only read the errors and if the o2 sensors are working or not, but do not measure their speeds. I was told that I need to hook up a digital volt meter to the o2 sensor to measure that. The auto stores also didnt have vacuum guages for loan. I checked with the dealer and ofcourse they'd do me a favor by only charging $90 for both checks instead of the usual fee per each check but I passed on that favor. I tried resetting the car computer today by pulling the main fuse but I dont know if that worked(see my thread about it). If resetting the computer doesnt help then I'll probably just replace the o2 sensors.

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The CEL will not come on until it is bad enough to trigger the ECM error.

Resetting the fault may make gas mileage improve, until the ECM figures out the O2 sensor or converter is bad,

then it will change operating parameters and your gas mileage will be bad again.

Edited by Bikeman982

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I wanted to reset it mainly because I cleaned the maf and wanted the computer to acknowledge it incase the setting could be different now. I may very well have to get new o2 sensors before its over with. Hopefully that and not a new cat.

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Mileage is now back up to 27mpg from the last tank that got 24mpg. Its not the usual 30+mpg so Im hoping the next tank will be improved back up to normal and stay there. If not then I'll replace the o2 sensors whenever I can but time will tell.

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