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Error Code P0420

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Old 02-28-2008, 10:27 PM   #1
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Unhappy Error Code P0420

I know there are several threads on this, but this is a little weird...

I had a new Magnaflow Catalytic converter installed about 2 months ago (the old one was rattling like a tin can). Everything was running fine until about a couple of weeks ago when my car started throwing the P0420 code *Catalyst efficiency low bank 1*. I figured that since I had a new Cat. Converter, that it was more than likely my O2 sensor going bad (after the Cat). I installed the new one this past weekend, but the CEL is still on. Right now I'm wondering what the heck to do. My Blazer runs fine... I just have this annoying light on. Any ideas???
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Old 02-29-2008, 05:30 PM   #2
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Re: Error Code P0420

i had the same code come up a while ago. i was just gonna throw a new cat on, figure at 120k it must be toast with how much soot flies out of the exhaust when i stomp on it. well luckily i have autotap, so i hooked up to my pc and what do you know, a bad o2 sensor on bank1.(not after cat) on driverside. so chances are you just need to find what o2 sensor(s) is bad.
not sure how else you will test the sensors. i guess just start replacing them. or spend that money on autotap or similar software there are a few others. and diag. it yourself.
im sure someone will chime in with a way to test your o2's

ps you could always take the ses bulb out lol
Old 03-05-2008, 05:40 PM   #3
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Re: Error Code P0420

So bank 1 is referring to one of the o2 sensors between the Cat and the exhaust manifold? It sucks that the readout doesn't tell you which one is bad.
Old 03-05-2008, 06:13 PM   #4
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Re: Error Code P0420

Bank 1 Sensor 2 is just in front of the cat on the drivers side. I replaced that one last weekend. Took all of 15 minutes.
Old 03-18-2011, 10:41 PM   #5
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Re: Error Code P0420

This is an 0BD II driving cycle to reset your monitors.They do not tell you this when getting inspection if you fail, "just drive it a few more miles" found out the hard way but it really works
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