Prius c left with key in overnight, woke up to the car running - what next?

Yes, it's fine. Don't worry.

 

Was the car left in ready mode? If so, the engine would have cycled on and off to maintain the inside temperature
and charge the battery.

 

That's the mode it is in when you are ready to drive. if you don't press the power button when you leave the car, it stays in that ready to drive mode.

 

Its fine.

 

The tank might be a few gallons low. Just add more. Otherwise, the biggest problem from having left it on overnight is that someone could have easily stolen it.

The tire pressure light is another matter. Either at least one tire is too low and went below the detection threshold during the overnight cold (pressure drops about 1 psi per 10F of cooling), or the thresholds are set too high, or a sensor battery is close enough to end of life that it temporarily failed during the cold night.

Read all your tire pressures before adding air. If none are significantly low, then a TPMS Reset may be needed to adjust the alert thresholds. If any are significantly below the recommended numbers on the door jamb label, you might have a slow leak or seepage, or just haven't been putting enough air in them previously. If it is a sensor battery issue, you will need new sensors soon. If the sensors have never been replaced, then they are nearing end of life.

If you don't have a tire pressure gauge at home, then get one now! They are cheap, and having one on hand is far easier than going anywhere else to check, greatly increasing the likelihood that you'll check pressures sufficiently often.

Also consider getting a tire pump. Some people already have shop air compressors. Most others get small 12V tire pumps. Some of us just use ordinary bicycle floor pumps, these are cheapest and are still sufficient. Having any tire pump on hand at home greatly reduces the hassle of keeping tires properly aired up.

No real concern.

The 2 bars you saw are exactly what we'd expect from this 'accident' of forgetting to turn the car off. There is no need to make a special charge-up drive now (unless it is going to remain parked for weeks), the next time you take it for a ride, the bars will go back up to normal. 6-ish bars for typical flatland highway driving, or anything between 2 and 8 bars for various hilly city driving scenarios.

 

What you did for quotes is perfectly fine, one of several ways to do it.

For a formatted box around the quote, just put a [quotte] and [/quotte] before and after the text of interest, with brackets, but using the word 'quote' instead of 'quotte'. I had to misspell it here to disable the function so that you could see the needed form.

To make attributed quotes look like what I did here, just click on the "+Quote button at the lower right, then delete any unwanted text between the bracketed QUOTE elements. You should see something like (misspelled again to disable and make them visible):

[QUOTTE="birdcatfish, post: 3249961, member: 198989"] .... [/QUOTTE]

but with text of interest in place of the " .... ".

 

I'm now putting in fresh sensors any time the old ones are more than 7 years old when tires are being replaced. I figure that if I don't, the old sensors will probably fail before the next tire change, causing both extra hassle and the additional labor cost to dismount the tires to swap sensors.

When changing tires, there is effectively no extra labor cost to replace sensors too. It is just the cost of new sensors only.

 

Actually we have some guys who leave their cars running all night on purpose. Some camp in it and want ac all night. Others hook up a 12v to 120vac 1000w inverter to run their refrigerator and internet during a power failure.

When a Prius is in a Ready "idle" state for a period of 15-30 minutes or longer, it will run the ac and 12v loads off the high voltage (hv) battery through the vehicle's hybrid system. When the hv battery gets low, the engine starts to partially recharge it. Partially is the key word. It does not fully recharge the hv battery all night long even if its left in Ready (running) state. Only when you drive the car will it "fully" charge (fully meaning ~80%).

Is running all night in a Ready idle state recommended? Not really. If the car was inside an attached garage, you could get exhaust fumes in the house. If it was outside, someone could drive it away. If the water pump failed, it could overheat. But all's well that ends well.

 

I used to drive to Dallas and sleep in a grocery store parking lot in my Prius. Ran all night, air conditioning was just right. Woke back up and off I went.