Cold weather - Check hybrid system?

I started a new thread because my issue doesn’t seem related to well-rested’s 12v battery thread (well-rested, I wish you good luck!). The reason I don’t much suspect my 12v is that it is only one year old, replaced at the end of 2017.

Yesterday was very cold by local standards: minus 28 F. It was errand day, so off I went: the C started fine. Being so cold, I warmed it up for about a minute before putting it in gear, then drove to Errand #1 – the recycling transfer point, a short trip of about two and a half miles, running the front defroster most of the way. Turned off the car, unloaded my recycling, turned it back on – it started and gave me the “Ready” light, and the ICE started normally, and then it went to the “Check hybrid system” message. Well… the place where I was stopped was safe enough from being a traffic hazard, but I had visions of sitting in a dead car for hours waiting for a tow truck, in twenty-something-below weather.

So I drove cautiously to Errand #2, the bank. Another short trip, about a mile and a half around 25 mph. Car ran normally. I went in the bank, sat by their nice gas fireplace, and called the Toyota dealer. He said I should have it towed to the dealership, but if it was running all right, I might see if I could drive it cautiously to get there. So that is what I did; this time about six miles, still being gentle with the vehicle. No problems.

At the dealership, they were singing a different tune; no, they couldn’t look at it that day. Or the next. All booked up. The first appointment available was a week from then, Feb. 7. But the service advisor suggested that I could probably drive it carefully and see how it does when the temperatures warmed.

By this time, my C had sat indoors in the service reception area for maybe ten minutes. I started it up to leave – no warning message. Thus encouraged, I ran the rest of my errands, four more of them, all short trips. And I drove my normal commute today in much nicer weather – it is up to around zero F. No problems, no error message, everything is running normally, including ICE shutdown and restart at some of the stoplights.

Anyway… have others of you who live in colder climates run into such a thing? I am guessing that it was related to the cold temperature yesterday, and with some driving and a brief respite indoors it warmed up sufficiently to be all right. Strange that it didn't go to the error message until its second start rather than immediately upon its first cold start.

I still have my service appointment for next Thursday, but am inclined to cancel it if the car runs normally for a few more days.