Prius doesn't seem to fully turn off

I'm really confused by your post. So when you press the on/off switch, the car doesn't turn off? The dash lights would be a good indicator if it's off? Everything would turn off......

If it doesn't turn off, all your dash lights would remain on...along with your radio, AC, etc.

If you don't want the engine to turn on, you would have approximately 15 seconds to operate under electric mode. So I'm not understanding how it doesn't turn off.

 

Bizarre. Make absolutely certain your 12V is good. The only way to say for certain is to take it to a parts store and have it load tested.

If you need to replace it, get a price on a genuine Toyota/Yuasa battery vs. a yellow top Optima. The Yuasa are only a little bit more at around $200.

 

So do you your dash lights remain on? If Yes, then could just be a faulty switch. If No, then it is beyond me!

 

It could be the combination meter acting up. Usually when it goes out it doesn't light, but yours could be hanging up. If the combination meter can't report speed to the engine control it won't turn off the car as you might be moving. There's an issue with reset timing and a capacitor on the combination meter. I think holding the power button for 30 seconds forces an off state.

Does this happen frequently?

 

I had a similar problem. It turned out that the 12 Volt battery positive cable connector was a little loose. I was getting intermittent resets, (momentary loss of 12V) and weird shutdowns that didn't shut down. I attributed that to a low 12 V battery, since it wasn't charging through the loose cable connector. I found the problem when I had zero 12 volts, (no dome light) and immediately went to the 12 V battery and discovered the loose cable connector.