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What is the rear cat converter for? There are no 02 sensors after it. Why is it even on there? The 2 front cats have a sensor before and after. I don't understand the purpose of the rear one.maybe ya'll can help me. Thanks
 

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The rear-most cat is the main catalytic converter. That's the primary cat that is required to keep emissions under control. Know too that the main cat is under the front seat area, that rear object some confuse with the cat is actually the muffler.
 

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There are no sensors for the rear cat, therefore no codes can come from it. If you have codes, it's from the mini cats
 

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What is the rear cat converter for? There are no 02 sensors after it. Why is it even on there? The 2 front cats have a sensor before and after. I don't understand the purpose of the rear one.maybe ya'll can help me. Thanks
cats need to run hot in order to be effective...like ~500°+F. the two upstream "mini-cats" heat up quickly because they are so close to the engine, and the combustion chamber is basically breathing fire directly into them. So when the vehicle is warming up, those are doing most of the emissions reductions. When the engine and exhaust stream are up to temperature, the main cat becomes efficient and is doing most of emissions reductions.

You can imagine this - if you start your Jeep and drive around the block once, then shut it off, the downpipe is going to be too hot to touch, but the muffler and tailpipe will only be warm. If you go for a 2 hour drive on the highway, everything is too hot to touch.
 
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