Stall due to dirty MAF sensor

Preach!

People are so often getting worked up when the triangle lights up, because they jump right to thinking they know what it means, and don't realize it comes on for any of a couple hundred different trouble codes from the HV control ECU and some of them aren't even big deals.

Even calling it "red triangle of deeeeaaaaaattthhhh" plays too much into that. What Toyota calls it—the master warning light—gives much more the right level of non-panic.

In your case, it was on because of the P0A0F, and P0A0F is just the HV control ECU saying "weird—for some reason the engine's not running".

 

Have you got a damaged air filter or air box, or leaky joint in there, so little bits of gradoo can get sucked in and land in the MAF sensor?

Maybe just take the air filter and air box out and dump / vacuum / scrub them up nice and clean and reassemble.

This really shouldn't keep happening, with only clean filtered air going by.

 

I second this.

Although I have never done that on a Prius I have done it on other cars. All the plastic before the throttle body comes off and gets a thorough cleaning and inspection. Sometimes one finds broken bits between the air filter and the MAF (or some other sensor) letting unfiltered air in which isn't immediately obvious when the intake is assembled on the car. Especially when it looks something like this:



Breaks at the bellows (roughly in the middle of this part) often open downward and cannot be seen without a flashlight and a mirror when the part is on the car. Other times the junction between two pieces has popped open a little, especially if the "metal rubber band" sort of pipe clamp (I think there is one all the way on the left of the image) is used, because those can break and fall off.

Also check any vacuum hoses along the path. A small crack in one of those upstream from a MAF can foul it.

 

Clean the snorkel. Easy for stuff to get jammed in the "U"
Kris