Prius (2010-12) :: Car Beeped And Suddenly Hit With Multiple Warning Lights

I drive my 2005 Prius 40+ miles each way for my commute. I bought it in the fall of 2007 with 56k miles already on it, and with my commute I'm up to 140,000 miles already.

This morning I was about 5 minutes from work, cruise control on, and deeply absorbed in listening to a podcast. I was startled out of my reverie by several things happening simultaneously. The car beeped, the cruise control kicked off, and multiple warning lights lit up on the dash, with a warning icon of some kind also on my MFD.

(Once stopped, I looked up the warning lights. They were: Master warning light; Check engine light, or "malfunction indicator lamp", according to the manual; YELLOW Brake system warning; VSC warning light. On the MFD, the Hybrid System Warning Light was on.)

I was on the highway doing about 70 and I had just crested a hill, so I allowed the car to coast on the downside while trying to access the situation. I cautiously pressed the accelerator, and though the road noise made it impossible to hear the engine, the car seemed to still be driving normally. The Energy Monitor still showed normal flows between battery, engine, and wheels. I had one final, short uphill climb before my freeway exit, so I chanced it. I took it easy and allowed my speed to decrease on the uphill so as not to push too hard, just in case. Once off the freeway, most of the remaining mile is downhill or flat - I can often make it to the office without the engine, and in fact I did so this morning.

Once at the office, I put the car into Park and grabbed the manual so I could identify all the warning lights before powering off the car. I turned off the Prius, let it sit for 5-10 seconds, and powered it back on. The brake system warning and VSC lights did not come back on - only the master warning light, and "check engine" lights reappeared, and "Problem" on the MFD was again replaced by the Hybrid System Warning icon. After the usual 10 seconds, the engine started normally and responded to the accelerator.

One additional note: After the freeway exit, my car is usually at 1 green bar or just below on the hybrid battery. Immediately following the freeway exit is a steep downhill that usually puts the SOC to completely full. That was the case again today, and as often happens, that full charge was able to take me the rest of the relatively flat, distance to the office at my usual 25-35 mph. I mention this because whatever might be setting off the warnings, the Prius still seems to be managing the charge level normally; at least in the admittedly short period I was able to observe it after this occurred.