P0431 Question
 

P0431 - post cat O2 sensor, passenger side

My questions are:
Would there be any signs it was going bad or are they binary - they work or they don't?

Any issue if I have to drive it a bit with it bad until the parts arrive from our site sponsor?

This is on my CSS.

The other possibility is that your primary catalytic converter has gone bad. I have seen that code a couple of times when I have driven long trips at a leisurely pace. First time I replaced the O2 sensors on that side. The next time I knew it wasn't the sensors, so I did two things. I stopped driving long stretches at a leisurely pace and the code reset, and I bought a manifold with a catalytic converter to replace the bad one. The code hasn't come up again this year, so the replacement manifold is still sitting on the shelf. I'll do the replacement at an appropriate time or when the code reappears and doesn't clear when I up the pace.

No issue at all. But the car won't pass inspection in states that check codes, like CA and MA!

I was coming back from a 3-day DE at Indy, so hadn't been driving at a leisurely pace. :)

Here in fly-over country, we don't do state inspections.

It won't hurt it at all. Drive on!

FWIW, I have a 2002 4Runner with 274K miles. every few months, I get a code for post cat O2 Sensor. I replaced the sensor a few years ago with OEM part but issue still happens. My guess is the CAT is weak, given its age and mileage. Thing is, I can reset code (I keep an OBD reader in the glove box!) and it may or may not come back for months at a time.

The heck with it!