We took Diane’s Prius to the mechanic today so they could work on it tomorrow; the “Check Engine” light and the red triangle of death stayed off on the drive.
The mechanic scanned the car and got a U0111 code, which means that the computer lost contact with the energy management system (or something like that).
His best guess is that the 12-volt battery is weak and having the car idling for a while during the smog test triggered the error, but they’ll do more research tomorrow to make sure it’s worth changing the oil. It better be – we have nearly a full tank of gas in the car!