Check Engine Light - Tough Question - Anyone?

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Old 09 Aug 2013, 10:10 am   #1 (permalink)
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Default Check Engine Light - Tough Question - Anyone?

Quick History: 2005 Scion tC, 90k miles, manual.















CEL came on in January, CEL went off by itself after 3 days.















CEL came back on after another week, stayed on, OBDII diagnosis, 2 Misfires, possible bad O2 sensory, and a possible P4020, bad cat.































Brought it to a bunch of places around me, everyone seemed dead set on it being the Cat, I said, ok, well I have another 11 months for inspection.































THIS was 7 months ago. Car does (and I feel like a pro now with cats) not feel like its sluggish, I get almost 400 miles to the tank (highway mostly, which is still way above what they say I should get), nothing is rattling, in other words, you would never notice, no smell, nothing.































Other day, I fill the car up to the brim, I start driving home (38 miles home) and almost home, I look down, light is OFF. I'm thinking the light burnt out, nope, then I search online, not much, but all the while I have a feeling its going to come back on, I didnt have the chance to scan it, so not sure if there were any codes, I will now to see if its a P0420 or whatever.































I did get a few answers stating that there might have been some crud on one of my O2's, which, dont ask why, not a mechanic, felt it was one of them all along, but again, not a mechanic.































And yes, every time I got it scanned or scanned myself back when this happened I did reset it, but none the less it came back on.































I actually saw one of the mechanics yesterday at the convenience store and he said if it was a bad cat, that CEL never would just go off by itself, it would stay on, but then he said sometimes its a mystery with these computers.































My gut is one of the O2 sensors are gunked up or just broke throwing this P0420 at me, but again, I have not scanned it this time, but odds are it will say 420, but my gut is that when I got that full tank of gas, the gas was rich enough to through the sensor off to think all was well, now that I am nearly out of gas, it just went back on. Have not touched the gas cap or anything.































What do you think? Thank you!
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Old 09 Aug 2013, 10:25 am   #2 (permalink)
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CEL came back on after another week, stayed on, OBDII diagnosis, 2 Misfires, possible bad O2 sensory, and a possible P4020, bad cat.































Brought it to a bunch of places around me, everyone seemed dead set on it being the Cat















--































LOLWUT?































Who would diagnose two misfires solely as a cat converter issue?































Sure, the cat converter could be toast after all that abuse from the misfires, but let's be real about what is the cause and what is the effect here.































Bad O2 sensors don't normally cause a P0420. A poor running engine does.































www.easterncatalytic.com
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