Hey all. I went to autozone to have this code checked out. I have a 1999 es300 and it stated it was code p0420 catalyst efficiency below threshold (Bank 1). Does anyone know exactly what the problem could be. What is bank 1? I know it's either an o2 sensor or the cat is bad. Maybe someone can give me a definitive answer. And don't worry, if it doesn't fix it I will not track you down. Thanks everyone!

 

I think I need to replace the front o2 sensor. Thanks again.

 

Well, Bank 1 P0420 is referring to Bank 1, Sensor 2 which is the O2 sensor (not to be confused with the two A/F sensors coming off of each bank). P1133 is definitely and A/F sensor code, and usually when you get one of those, reset the CEL, and it still comes on, that narrows it down to the A/F sensor (and not the ECM or a strange sensor reading). With the P0420, this is something common vehicles where I live experience at some point, given the gas and high altitude. However, to narrow it down to either an O2 sensor or the cat, requires examining either the resistance of the O2 sensor AND/OR doing an gas analysis (like an emissions test) to see what is coming out of the cat.

 

I had the same code (P0420) after I replaced the Exhaust pipe that included the Cat with an aftermarket one. Car drove fine for a couple of weeks and then WHAMO!!!..............code P0420......I checked everything, A/F sensors, O2 sensor - all was within Toyota specs.

To fix the problem so I could pass Ma. smog inspection rules, had to install an O2 simulator.

Here's a link to my thread about this problem...
https://www.clublexus.com/forums/sho...ighlight=p0420

HTH you
Good luck!

 

Thanks everyone. I'm taking it to toyota on thursday for a diagnostic check. I think the cat is bad. it rattles when I turn the car off which means something can be loose in there. Sensors and codes are such a pain.

 

be prepared for a HUGE repair bill if it is the cat.......that pipe goes for almost $1200 plus installation......