P0420 brainstorm thread

So i have a '16 trd or with 80k on the odometer and ive had an intermittent p0420 code keep popping up pretty frequently. Took it to the shop and the said the cats and o2 sensors are all fine, had to take the truck back for a trip but ill be bringing it back to them later to continue diving into but after searching around and finding kinda minimal threads on it i thought id ask you guys if youve got any leads i could suggest them to look at. Tacoma quirks or something.

 

Any evidence of rodents?

 

None that we've found, no. But thats a good suggestion

 

Do u have access to an OBD2 monitor? It'd be nice to look at fuel trims / 02 data when the code pops up.

 

Did they actually test the O2 sensors? Normally you would force the system rich by spraying brake clean into the throttle body then force it lean by creating a vacuum leak.

 

It's pretty simple. If they look at the rear oxygen sensors and they are either sweeping quickly from rich to lean or are under or above 670-690mv then the cats are bad and require replacement.

 

All I’ve got myself is the basic OBDll reader, the impression they gave me is that they tested the sensors and they tested perfectly, but whatever is making them trip is a random “flicker” moment. It’s just happening often enough(two drive cycles in a row) to throw a code.

Ive got an appointment to bring it back to them in a couple weeks, so now that I know a little more about how they should be tested or how they should be reading I’ll ask them some more specific questions about it.

The only things I’ve found from searching on here is people randomly having bad cats from
the factory or the exhaust gaskets not sealing and fresh air disorienting the sensors.

 

stock or aftermarket ypipe?

 

gas cap

 

They need to monitor while performing the driving pattern for the heated O2 sensor and then the driving pattern for catalyst efficiency.
It's probably a good hour worth of driving...

 

It’s completely stock, threw on a new gas cap for shits and giggles at the start too.

Good to know, I’ll suggest this when I drop it off

 

Well, the shop couldn’t 100% figure out what was wrong. They said they tested the cats several times and couldn’t get it to fail. It got close to reaching the low threshold for failing but never actually failed for them. So they said to bring it back when the light was more consistently on.

So I stole my brothers code reader and grabbed the freeze frame data for when the light triggered and the only abnormal reading to ME is how much lower B1S2 is. Which makes me lean towards throwing a new o2 sensor in.

 

This maybe under factory EMISSIONS warranty. Most Converters are under warranty for 100k. Call your dealer. PO 420 is usually a hard code for converter efficiency fault

 

**UPDATE**

Took the truck to the local Toyota dealership, they confirmed the cat was the fault, it is not covered under any warranty at 87k miles on the odometer. Luckily I worked there briefly so i got a friends and family employee discount for a grand total of $1,000 out the door including an alignment. On a side note they also replaced my apparently leaking steering rack and driver heated seat under warranty, so that was nice.