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Old 07-11-2017, 02:16 PM   #1
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08 scion xb. after the exhaust rusted apart i had to replace the cat and everything behind it with aftermarket exhaust. Ever since then, i get an intermittent CEL and the code is p0420. if i disconnect the battery the light goes out for a few miles, then will come back on. and some times the light does go out by itself by just driving it..

i see alot of people get this code with installing headers and such. but this is just an aftermarket cat-back system... any ideas?
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Old 07-15-2017, 04:02 PM   #2
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Did you install a stock replacement cat or an aftermarket "performance" one? Who did the work?

See this link to read about your code. http://www.p0420.com

The cel turns on when one of the continuously running self diagnostics tests fail. Disconnecting the battery resets the self tests from the beginning. It sometimes takes a little while for it to run through all the tests until it gets to the one that fails. That's when your light turns back on.
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Old 07-15-2017, 05:24 PM   #3
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Did you install a stock replacement cat or an aftermarket "performance" one? Who did the work?

See this link to read about your code. P0420 DTC Code - Catalyst System Efficiency Below Threshold (Bank 1)

The cel turns on when one of the continuously running self diagnostics tests fail. Disconnecting the battery resets the self tests from the beginning. It sometimes takes a little while for it to run through all the tests until it gets to the one that fails. That's when your light turns back on.
its was an aftermarket oem replacement, not a performance one. I installed it myself. just a bolt-on. nothing too major.
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Old 07-15-2017, 06:21 PM   #4
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Did you have the code before you started the work? Did you install new O2 sensors?
Keep in mind my mechanic cert level is strictly "shade tree."
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Old 07-15-2017, 06:40 PM   #5
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Did you have the code before you started the work? Did you install new O2 sensors?
Keep in mind my mechanic cert level is strictly "shade tree."


same 02 sensors... I got the code a month or so after installing the new exhaust... you and I share the same cert. I did body work for a living years ago... but this obviously isn't body work,lol
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Old 07-15-2017, 08:10 PM   #6
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That's where I'd go with it. Change the O2 sensors, or just the downstream one. Mainly cause it'll be cheaper than another brand new cat, which might be the only other thing to cause that code.
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Old 07-17-2017, 07:47 PM   #7
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That's where I'd go with it. Change the O2 sensors, or just the downstream one. Mainly cause it'll be cheaper than another brand new cat, which might be the only other thing to cause that code.
im currently trying the laquer thinner in the fuel tank, since that is the cheapest to try.... ill report back with results
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Old 07-17-2017, 08:30 PM   #8
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Never heard of that. Let me know how that goes.

I thought for sure we'd get other people chiming in for this one.
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