CEL comes on after gas fill?

You will need to get someone to read the code. Before anyone can answer your question.

 

How many times in its life have you "topped off" the gas tank resulting in gas coming back up out of the fill hole?
Gasoline belching back out?

 

Ema does this as well sometimes and it is especially prevelant when I put premium in her or run a bottle of STP cleaner through her with a new tank. If the code you are getting is the P0420 it is the catalytic converter that is most likely the issue. It could be the O2 sensor but most likely you are looking at a bad Cat.

If you can post the code you are getting with the CEL I am sure you will get a lot of feedback on her with good thoughts and ideas.

Happy driving,
Chris

 

Why are you running premium?

 

Most premiums generally have more cleaning additives in them and will burn hotter. I generally try and do it every 5-10 tanks. Its especially effective filling before a long trip where I know I am going to be driving for 500+ miles. Acts as cleaner. The few tanks after a premium run are always higher MPG's for Ema.

Chris

 

Actually higher octane fuel has a slightly lower combustible property than does lower octane fuel. High octane fuel is for high compression engines, like a sports car or a motorcycle or turbos. High octane lowers the point of combustion. It won't do you any good in the Prius, and isn't cleaner or better at all, and doesn't burn hotter.

 

Exactly Schmop.