This code has been coming on and off for about 3 years now. Just before i went to get an inspection it decided to come on and now weeks later won’t go away. So I figured I might as well fix it now. The code is catalyst 2-1 efficiency. This can be exhaust leak, bad cat, or bad 02 sensor. I plugged my scan tool in and watch the 02 sensor reading and noticed that the bank 2 sensor 2 is reading 1.2 V at its peak and it is all over the place. The others don’t go above .8V which is correct. My question is that should i just replace that 02 sensor or is there more tests i can perform to prove it’s either the cat or 02 sensor? I know a bad cat may cause high voltage to that sensor but i’m not too sure. Thanks

 

What year is the truck? Some have 3 cats/4 O2's and some have 1 cat/3 O2's. My primary indication would be a bad O2 sensor. With that said, 1.2 volts is a pig-rich condition. You'd notice by that point, the fuel trims would be so far negative it's not funny and power would be dramatically reduced.

 

LOL yes the short term fuel trims are surprisingly only around -10. It’s an 01 dakota 3.9 cali emissions so it has 3 cats and 4 o2s. I’ll replace the o2 first. But if that’s not it do i replace the mini cat on bank 2 or the main cat?

 

Also it runs like ****. Has rough idle but rpms are steady. I’ve already done a proper tune up and did plenum gasket as well as valve cover gaskets. Has 110k miles

 

My 01 3.9 in same emissions trim was happy when I put new upstreams on it. It was even happier when I dropped the Y-pipe down and found the mini-cats completely coming apart and blocking themselves up. I turned the assembly upside down and all kinds of semi-molten honeycomb and mess poured out. I ended up scraping the whole thing and running the main cat only, with downstreams extended behind it.

And taking away 10% of fuel is alot for an EFI engine.

Not sure where you are at. But if you have the means, you might drop the Y pipe and dump the cats out or at least do a visual inspection. Eliminating them and relocating the downstreams is much more involved, even if it's "the right" thing to do. Unless you actually live in Cali and they know that there should be 3 instead of one.