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#14: 02-07-2013, 06:12 AM
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Originally Posted by firebox40dash5 View Post
You can disconnect the battery or pull the ECU fuse to "clear" the codes. It's possible it'll come right back, or it might not. Sometimes you just get a "flyer" outside of the parameters that'll set off a P0420 every once in a while, sometimes there's a real, constant problem, whether it's a cat that's truly no longer efficient, a bad rear O2 sensor telling the ECU the cat is messed up, or something causing it to run rich all the time. Honestly, without a way to watch the outputs of the front and rear O2 sensors, it's about impossible to pinpoint which one of those it is.

I generally recommend a new (quality, meaning Denso or NTK, IMO) rear O2 sensor. They're rarely over $100, and usually are the cause of a P0420 on a car that's otherwise running right.
I usually do go with a brand name on parts.

Would rear 02 sensor be causing the gas usage and smell?