07 Honda Pilot check engine light

P0420 codes aren't a cheap fix way more often then not. A lot of the time in inspection states it tends to be the end of the line for the car where you sell it for scrap or out of state buyers in no inspection states who do not check emissions.

However, P0420 doesn't 100% mean bad cats - sometimes it's just bad 02 sensors and a lot of cheap scanners fumble in discriminating the code. Scan the car with a all system scanner like the Innova 5610 or 5410 (or the many bidirectional all system scanners you can buy online with lifetime updates -- or an OTOFIX with 2-3 years included) and see if the code is a catalyst error or sensor error (NOTE: you can use live data as well to determine which is which if you can find someone locally you know like a friend who works on their own cars to interpret it if needed). Get a borescope camera and make sure there is no oil in the pistons first - that can (AND WILL) damage cats/sensors. If there's oil in the cylinders, you will need to replace or rebuild the engine, or rebuild the upper block with the cylinders. Something like this: https://www.amazon.com/Borescope-Endosco... -- cheap way out is to disable the cylinder deactivation if yours has it, but you will need to code it out with a tune in many cases. It shouldn't cause an issue with inspections since you're deleting it in code, but you probably should look into that.

• If your state uses CARB you need this one: https://www.vcmtuner.com/products/vcmtun...

If it's a sensor error, I would just go through and do them all in a emissions testing state to be sure. If it's the cats, see if you can find a private seller with a used complete exhaust or you will need to buy the cats new. Junkyards legally cannot sell cats without testing to make sure they still work, so they just don't - but private sellers who will take cash and silence will make it happen ;). If that doesn't work, see if you can find a OE cat that's known to be reliable as a bad 3rd party cat often creates the same issue. OEMs can be $1k+ and the dealers mark them up exploiting the feds making used ones hard to come by.

The good thing is this: If you had it done recently, you often get a 5 year warranty on new cats - try and use that first. If they will not honor it or it was a 3rd party cat, see my above comment on replacing them as a cheap way out.