Triangle of Death....but car drives fine

Yesterday I was about to turn left at an intersection a mile after leaving home, and the "Triangle of Death" appeared, along with check engine lights on the dashboard and display. I thought it was the software problem that has been mentioned in the news (and here) recently, where the engine won't kick in anymore...but everyting worked like normal.
I pulled over, restarted - same lights but still everything worked.
Drove home, and restarted - same.
Did the procedure to turn of the "Maint. Required" light which the Toyota dealer had left on a few weeks ago. Restarted - Triangle gone, Check engine still there.
Restarted a couple more times, and made sure the gas cap was closed - no more lights.
Everything still works fine. Any clues? Should I take it to the dealer?


2004 AM package, 25000+ miles, 48 MPG avg, no previous problems, tank half full, warm temp

 

The engine definitely still ran as usual. That's the first thing I tested as soon as the warning lights came on. I saw the engine run on the display, heard it, and even felt the vibrations (by touching the dashboard).
The car still runs fine, by the way. We may get the codes checked later (but not until after our European vacation)