P0420 code after replacing catalytic converter, slightly overfilled oil

The distance between the two indents on dipstick is 1.5 liters, or 1.6 US quarts (rounds to roughly 1.5 as well), noted in Owners Manual. Still not a lot of overfill.

 

The "variable" for an exhaust leak is the gasket at the spring loaded manifold connection. It can seal at idle but leak when the powertrain moves under load. I have found that only a Toyota gasket will reliably seal any cat.

That said, the P0420 cat test is run at idle, and likely fails because you have a cheap AM replacement cat. Less than 1 psi back pressure is "nearly nothing". Normal for most cars is under 2 psi when snapping the throttle fully open or when driving under high load.

If A/F and O2 sensors work properly & fuel trims are 0 +/- 10%, then put another cat in.

Posted via the PriusChat mobile app.

 

And you must use the factory donut not the one that came with the new cat. Here's the part number:


As a sidenote my bought new 07 at 12 years later @150K miles started to use a very small amount of oil. 2 things I found stopped it. Move up to a 40 weight oil and overfill it about an 1/8th of an inch.
And check the dipstick minimum once a week after it has sat overnight and before starting the car and never let it get below the full line.
3 years later when I sold it it still did not any oil.