2005 Prius. Manufacture date Dec 2004. 40200 miles. Has had 50P ECM Reprogram and 60C steering shaft. 5k service was done just Friday, 2/1. Drove normally over the weekend. Filled up on Sunday & drove to and from super bowl party after that. Unusually cold for here this a.m. (40-45F). Started normally. Proceeded about 1 mi downhill to red light; noticed battery full at bottom of hill. Got a BEEP, red exclamation point, check engine, + "PROBLEM" on MFD. Restarted car; same lights. Was able to turn right and go into gas station; seemed to run normally. Turned off and reseated gas cap (did not seem obviously loose). Turned on: exclamation point, check engine, + red exclamation car (hybrid malfunction) on MFD. Consulted manual ("Take to dealer immediately") and called home about a ride from the dealer; got a suggestion to make sure it didn't blow all its oil out of a mis-seated filter (happened to us on another vehicle!). Turned off, checked oil (slightly overfull), turned on: no abnormal lights. Called dealer. They suggested since the lights went off, I could drive it there, but it should be checked. Drove there uneventfully. They hooked up the computer, saying "probably the gas cap," then "Huh, I've never seen that before: DC/DC converter malfunction." I left it with them for a thorough checkout. They called a few hours later and said apparently I'm not the first; the Toyota database said to replace a computer with an updated version. They said it'd be under the hybrid warranty and ready tomorrow. I asked for the code: P0A78. From a little light googling, this seems to be related to TSB 02505, which seems to suggest an inverter replacement rather than ECU. Any thoughts? I suppose it's possible there are other codes they didn't read to me.