Check Engine Light

So my 2009 Prius' HID headlamps were acting up so I brought my car into the dealer today and they replaced the one that wasn't on per the Toyota settlement.

But when I got a call to pick up the car the service adviser said: "Did you know your Check Engine light was on?"

I explained that it most certainly was not when I dropped the car off 90 minutes earlier.

The tech checked the computers and got 3 codes: one for "Engine Failed to Start," one that was like "Low Battery Power" or something like that and another that was similar.

I asked if the computer time-stamped those codes because they most certainly didn't happen while I was driving. The light never came on.

I have had no performance issues with the car and it's only 600 miles out of warranty (36,600 miles!). They think it might be an issue with the high-voltage battery (which would still be under warranty) but now I need to wait 2-3 hours while they "look into it."

Has anyone ever heard of this? I feel like I'm being scammed. Does the computer time-stamp when error codes happen?

 

So they said it was the "mass airflow sensor" had to be replaced. Would that give the error messages "Engine failed to start" and "Low Battery Power"? Anyway, they replaced it saying it was under warranty so I was happy for that, but this all seemed a little bizarre to me.