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Discussion Starter · #1 ·
Popped code P0420 "Cat converter below threshold Bank 1" last night.

I am making assumption it is an O2 sensor and will run the test procedure from Chiltons this weekend but which of the 4 sensors should I be checking? Is bank 1 the front bank on the Duratec? Is it the sensor before or after the cat (I am guessing after)?

Thanks for advice
 

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Definitely take a look at the rear sensors. The front two sensors control the air/fuel mixture in the combustion chambers, while the rear sensors really only check the health of the cats. I would say that bank one would be the front bank of cylinders, and taht you probably need a new cat. Especially if you're at 170K and they've never been replaced. Also, if you'er going to get one replaced, you might as well get the other one replaced...it's easier that way.

JR
 

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Discussion Starter · #3 ·
wouldn't you get some kind of engine performance change such as lack of power or stalling if the cat was bad? I haven't noticed anyhting like this on my car. I will pull the O2 sensor , leaving the hole unplugged and see if I get any kind of RPM change in the engine, if none I would think the cat is clogged or do I have it reversed?
 

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I don't think that you would notice a change on a 170K engine. On a 20K engine, yes, as you'll notice a significant drop in power, but with 170K, you'd be hard pressed to notice a whole lot of difference. You might also smell sulfur, as I've been told that a clogged cat will typically produce sulfur smelling emissions.

JR
 
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