Catalytic Converter, P2195 Conundrum...

Hello - This is my first Prius and my first post. Unfortunately, it's about a problem.

I 'inherited' a 2011 Prius, 219K miles, from my girlfriend after the head gasket blew. Water ingress into the combustion chambers. I ended up replacing the engine with a 50K mile JDM unit and the thing ran fine, until... the dreaded P2195 DTC. So, here I am, hat in hand asking for y'all's sage advice. The facts of the case are this:

Pulled the upstream wide band AF sensor (B1S1)
- It's a Denso part
- Heater element shows 3ohms cold, 6+ ohms when hit with a blow torch
- The voltage swings from 0v cold to 3-4+ volts when torched
- Reaction times seem pretty quick when I put the heat to it then take it off.

Reinstalled that sensor - still popped a P2195

So I whipped out the ODBII computer and tracked a few numbers. The ones that caught my attention were the catalytic temperature readings.

- Cat Temp B1S1 is always 100' higher than B1S2. To me this is backwards.
- B1S1 output voltage is always above 3V

Finally, the exhaust smells like rubbing alcohol. Pew!


So what do y'all think? Bad cat? Bad AF Sensor? Bad Both?

Any advise would be appreciated. These parts are a bit on the pricey side and I don't want to shotgun parts trying to fix the problem.

I'll tell y;all the whole story of how she did it, what I had to do to 'rescue' her and what the fix ends up being when this is all over - hopefully soon!

Thanks!

 

Not very long. About 50 miles or so before the check engine light came on.

Peter, we're showing our age. I haven't heard of anybody washing a catalytic converter in over a decade! If you think the cat is the main issue, I'm inclined to invest in a new one. ** This car has turned into the pet project, money pit from hell but to me, it's like adopting a rescue stray you've been fostering for a while. It just grew on me after a few weeks.

** Ok had to edit this post. Just watched a video from Scotty Kilmer where he suggests doing that exact thing. Given that the car was driven quite a few miles with radiator coolant infused steam coming out of the exhaust, it may very well be clogged. Hmmm... I got the time. I might try it.

 

So all's well that ends well ...

Becoming frustrated with the scan tool's contradictory readings, I decided to take matters into my own hands and go straight to the 'horses rear' and read the cat temperatures directly with an infrared thermometer. My and the mechanic's thermometers agreed, the front of the cats were cooler than the rears by around 100'F, in both cases.

This new information, while not quite a smoking gun, certainly put the spot light on the front AF O2 sensor (B1S1) as the source of the P2195 problem. So I replaced it. The logic being that if the cats do turn out to be bad, I would go ahead and replace them and the sensors as well. So why not start with the most likely sensor causing the problem.

And it worked!

The pending codes were cleared by the scan tool and permanent P2195 error went away after 3 drive cycles and 75 miles of driving around. Plus the rubbing alcohol smell is no longer coming out of the exhaust. Yippee!!

The engine is fine. In fact, it runs GREAT! Smooth as silk, powerful (for a Prius) and very quiet.

But the scan tool still reads the cat temps backwards even though the actual temps (under the car) are correct. Go figure.