Hello I just bought my mother a 2000 4Runner sr5 and everything was good until about a week ago when the check engine light came on. I ran the code and got the dreaded P0420. Now, there is a slight rattle when really accelerating so it leads me to believe it is the catalytic converter like the code says rather than a bad o2 sensor. Maybe I am wrong? Ok so I know there are two catalytic converters but I am not sure if I should replace both of them or just one? If I go the aftermarket route, is there a certain cat that is preferred by people?

Also, I am able to get my hands on a used 2001 Catalytic Converter set up with both cats. Will this be a direct bolt on?

Thanks for any help you can give me.

I have the same code and a little bit of acceleration hesitation. I just keep clearing it because it's pricey to fix. I have 1 year old sensors and if it really is the cats it would be troublesome to do myself and pricey to get it done. Problems with aftermarket ones I've heard is that they might not be up to the specs of toyota so the code still might pop. I've read people change theirs out with cheap cats and the code still pops. You could look into just buying the simulators. I recently asked this too you also might be ok if you're in a state that doesn't care about emissions. Personally I'm just gonna flush it with some techron or seafoam or something. I've heard some rumors of the lacquer remover I believe. Worked for some but caused problems for others.

If your able to get your hands on used 2001 setup, that's both a good and bad thing. Good in that you have the parts, bad in that unbolting what's currently on your truck can be difficult. I wound up taking a Dremel to cut off the nuts, then drilling out all of the studs with some really long drill bits from Home Depot (couldn't get the drill close enough for regular length bits to work). What a pain that was.

If you don't want to use a simulator, I'd recommend just buying a $50 universal converter and having an exhaust shop weld it in.