P0420

I don’t think anybody will be able to tell from that freeze frame information if it’s catalytic converter or oxygen sensor B1S2.

You really need to watch live data from the sensors to be sure. And it might not be easy even then. But since you get the code pretty consistently it shouldn’t be impossible to tell. How much oil does your Prius consume?

 

You most likely need a catalytic converter, p0420 is almost always the catalytic.

Pay your registration fees early so you don't get a penalty.

You can try cleaning the catalytic or replace with an after market one

 

What city are you in? You would need to know people to get this done

 

Your two O2 sensor readings tell OPPOSITE tales....

The Front (Wide Band) sensor indicates a LEAN condition, while the Rear (Narrow Band) sensor indicates a RICH condition.

I'm not super familiar with the specific output voltages of the Toyota WB sensors, but all are more volts = more air (lean).

Since we know no fuel was "added" to the exhaust, it is apparent that the two sensors are not in agreement on what the actual air-fuel ratio is. This is further evidenced by the equivalence ratio and fuel trims which are not the same for the two sensors (if I am reading the scanner's data in chronological order).

The wide voltage variations of the rear O2 sensor suggest a bad cat, but the higher than normal voltage of the Front O2 sensor and fuel trim, suggests at a minimum, more than one potential issue. With the readings of the Front O2 sensor suspect, it would be unwise to jump to the conclusion of "bad cat".

 

I'd take a closer look at the O2 sensors. The front in particular seems to be alternating between a normal'ish range with ~.6V swings, and much smaller ~.2V-.4V swings. The graph of narrow band O2 sensor voltage on this page shows swings that are far more consistent than what your graph shows. The graphs of downstream O2 sensors also look more consistent than what you're seeing, which could be from the upstream sensor going sideways.

https://www.discountconverter.com/tech-tips/news_page.cfm?Key=catalytic_converter-&News=218

Also, a new narrow band O2 sensor is a lot less expensive than a new cat. You can get temporary operating permits from the DMV is need be. I think the max is 2 months or so. You can PNO it and get a 1-day moving permit for smog after you fix it. For what it's worth, I have 3 Toyota's with ~700k miles combined and I've never had to replace a cat converter.

 

Was specifically referring to WB voltages in my earlier post.

For reference, typical BOSCH NB O2 sensors respond as ALX suggests.

 

ALX,

How did you end up resolving this issue? I have a similar problem...

 

P0420.PRIUS 2007 TSPIRIT
Can anyone tell here which sensor is not good and have to be replaced?

 

View attachment 177675 P0420.PRIUS 2007 TSPIRIT
Can anyone tell here which sensor is not good and have to be replaced?

 

No. Get techstream and tell us the codes