Hello all. Hoping someone can shed some light on my 01 SR5 issue. I have a persistent PO420 code. I can't afford new cats right now, but just curious why the code only comes up when 4 wheel drive is used. I changed the donstream O2 sensor with denso, cleaned the MAF, new air filter, PCV valve and seafoamed. The code was off for 3k miles. Used the 4wd yesterday and boom. Comes back on. This has happened twice now in the last few months. Last time it had 2500 miles, used the 4wd and came on within 50 miles. Maybe because the engine is working harder in 4wd? It runs good, no rotten egg smell and get about 18.5 mpg on the highway. There is an exhaust leak after the muffler too. Not sure if that would affect anything

Thanks in advance for any responses and advice

Tell us, about how Fast are you traveling while in 4WD?

I'll bet it's about 5-15mph, yes?

If so, that is a Feature of our beloved Runners!

Guess who else's does it too?

Enjoy it otherwise -

The most common cause of catalyst efficiency codes is an exhaust leak near the cats or O2 sensors. Check the flanges and gaskets of the converter. Check if there are any small holes on the converters where the heat shields or hangers are welded on. A small leak that you barely notice can set this code if it is near the downstream sensor especially.

Try running a can of Seafoam through it. I'd pick up two bottles, one for the gas tank on next fill-up, and another to throw a splash in the oil.

Cheers

Thanks for the reply. Driving in 4H around 40-45 mph. I didn't realize this was an hidden feature lol. Maybe I'll just wait till spring when I know I wont use 4wd anymore. That or try the spark-plug anti-fouler method for the O2 sensor

Yeah, I will definitely do that. I can hear a leak. There is one after the muffler, but maybe there are more. Thanks!!!

Or just reset it like I do via torque while driving, takes all of 30 seconds and 3 buttons....then worry about something really tangible like lunch....

explain please i don't mean lunch, I mean 30 seconds and 3 buttons