It is definitely a tricky one because it can be anything from a hole in your catalytic converter to a bad O2 sensor. It can also be your $2000 cat that needs replacement (very unlikely imo). I'd check for leaks first and then replace the post cat O2 sensor. Only use OEM Denso....I think Toyota made the catalytic converter performance threshold way too sensitive.

You can test your O2 sensors with a multimeter and check the fuel trim using an OBD reader before doing anything.

 

I have an appt on Monday to have Toyota to scan it. I’m hoping it’s just an O2 sensor and they can narrow down which one. My dad who’s been a mechanic all his life wants me to take it in to have them narrow down the generic code it threw.

 

If they tell you that you need a $2000 catalytic converter I would still do my due diligence and check it myself...I remember when this happened to me my heart dropped when I looked at the prices for a new cat. Luckily I was able to clear it but it took me a while to isolate the problem.

 

I definitely will. My dad wants to see what their reader says since mine is just a standard one. If they say something outrageous my dad will come and check it out for me.

 

I had a 430 and 420 for long time...did O2 sensor replacement...no help... did Lacquer thinner cans and 92 octane gas...and heat, smoke and leak test...plug sealed up some exhaust flange leak....checked all vac hose and what not...ran obd2 scanner, fuel trims, O2 live data waveform which was bad....still bad showed 430/420... So I replaced the rear cat bank1 and code 420 bank 1 went away.....but I still have check light on with 430 bank 2 showing up still...reset, clear and ran several time...and code 420 bank2 still shows up every time..... so My next project will be R/R catalytic converter....

I put in a toyota part rear cat in...was around $470 for cat and gaskets and some new flange bolt/nuts.
I was pricing front cat 430 bank2 online toyota dealer parts....is around $550 or so.... I will replace it soon as next smog is up...but the numbers and wave form is still not that bad right now... my van is 2005 le fwd with around 270k miles so far.

 

Few questions:

1. What is the lacquer thinner can thingy?
2. Have you tried using Cataclean? I put it in an almost empty tank and drive it on the highway in 2nd gear for about 15 mins. I actually do these "Italian tuneups" on all of my cars a couple times a year...Even the Prius.
3. Did you try measuring the pre post cat temps with the thermometer to verify that it was working?
4. Is it mostly highway miles or city?

It does sound like your cats are dead since the code went away after you replaced it.

 

Yes sir I had the same issue on my 2011 Sienna LMT and I replaced both sensors on that bank and still would get the codes intermittently. I kept resetting codes but finally gave in and bought and replaced the catalytic converter. Reset code again and it fixed my issues. I also noticed better power and pick up when driving not to mention my gas mileage went up as well. The cheapest place I found for parts being OEM was from ordering online at Longo Toyota Service parts in El Monte, Ca Good luck to you! Kevin

 

According to Toyota today the O2 sensors are fine, but the converter needs to be replaced.

 

On my Gen-1 Sienna, the catalytic converter was perfectly fine through its lifetime of 250,000 miles, when the frame rusted out. The sensors lasted only about 100,000 miles, throwing emissions codes. Oxygen and A/F ratio sensors age and fail to function properly. Replacing all the sensors alleviated my 2002 Sienna's P0420 code.

So, what would it be about the newer generation Sienna's converter, that it fails so early, yet the sensors live? Is the converter cheaper? Does the engine run rich and clog the cat? Or is it really just the sensors? Or is there a leak in the exhaust, somewhere, confounding the ECU?

A catalytic converter should last the life of the vehicle!

 

On my Gen-1 Sienna, the catalytic converter was perfectly fine through its lifetime of 250,000 miles, when the frame rusted out. The sensors lasted only about 100,000 miles, throwing emissions codes. Oxygen and A/F ratio sensors age and fail to function properly. Replacing all the sensors alleviated my 2002 Sienna's P0420 code.

So, what would it be about the newer generation Sienna's converter, that it fails so early, yet the sensors live? Is the converter cheaper? Does the engine run rich and clog the cat? Or is it really just the sensors? Or is there a leak in the exhaust, somewhere, confounding the ECU?

A catalytic converter should last the life of the vehicle!

Not sure. Unfortunately with mine it has multiple problems and it’s time to let it go. Between the ac not blowing as well as it use to, there is an oil leak, since we have had it it eats through tires (if we are lucky we can get 30,000 miles).

 

I can recommend the You Tube channel "The Car Nut" for great inside info on Toyotas from a well experienced mechanic who works at a Toyota dealership.