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Nuts & Bolts: Bad Kitty

Posted in How To: Tech Qa on July 18, 2018
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Dear 4-WHEEL & OFF-ROAD: I have a 2004 Jeep Wrangler Sport that I just bought with 133,000 miles on it. It’s equipped with a 4.0L and a Dana 44, and I feel like I got a pretty good deal. The previous owner said he cleared a check engine light, and sure enough, it came back on when I was driving it home. The code is P0432, which has something to do with the catalytic converter. Cats are expensive, so I was thinking I’d start by just replacing the O2 sensor. What would you do?
Henry L.
Via nuts@4wor.com

If it’s throwing just code P0432, an O2 sensor probably isn’t going to fix it. That code indicates that the catalytic converter for bank 2 is below efficiency, which is a nerdy way of saying it’s not working right anymore. On your 2004 Jeep there are actually three cats: two upstream and one downstream. The upstream cats are the ones you need to be concerned with, as these are the ones that are monitored by O2 sensors. There are two sensors for each bank, one ahead of the cat, and one behind it. Bank 2 is going to be the rearward of the two cats.

We’d start by pulling the downstream O2 sensor and taking a look at it. If the metal cage that’s around the tip of the sensor is dented or has any foreign debris other than carbon on it, the catalytic converter is no good. Any dents or debris are caused by the catalyst inside the converter breaking down. You can also disconnect the exhaust downstream of the cats and see if there’s any debris in the system. If the cat has gone bad, more than likely you will find a large amount of debris in the third cat that’s downstream of the other two.

Replacing the bad cat will require welding, but you can use an aftermarket cat if you live outside of California, such as those manufactured by MagnaFlow (magnaflow.com). You’re going to want to do your best to shake all the debris out of the third cat, but we wouldn’t bother replacing it unless you see evidence that it, too, has broken down. If the third one is in good shape, it’s unlikely that much stuff made it all the way to the muffler. We would recommend replacing the cat even if you live in an area without emissions; catalytic converters actually do reduce emissions, don’t really impact performance, and without one you’ll always have a check engine light.

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