Coasting down a hill, lightly braking, then...

An update on my obsession...

I spoke to a Toyota shop foreman and stumped him when I gave him a detailed account of what happens. The best thing he could come up with was that the system is sensing I could overcharge the batteries and they are firing up the ICE to burn off charge? I'm dubious.

And now it seems to be happening a little more often. It seems totally unnecessary still.

More data:

Okay, so when I'm slowing down and it happens, the braking pressure changes quite a bit. It almost feels slightly unsafe. So here I am slowing down with the recharge bar right above the white dotted line. I have 4 bars of charge with no accessories on and the weather is 50ish. The ICE fires up and the brakes get much more loose or soft. I cannot confirm if the brakes tighten up after the ICE shuts back off. Now during this I don't lose braking ability per se, I just have to press my foot down harder when the ICE fires up to maintain the same deceleration point. It's similar to what it feels like when you're coasting to a stop at a light and you're under 5 mph or so and the regen brakes disengage (the brake pedal gets lighter and you have to push harder).

Has anybody experienced this exact same scenario? If not I'm wondering if I am experiencing some kind of brake hydraulic issue and the ICE is firing up to build pressure?

In the future, if someone could pay attention when they get off the highway on a decent-length off ramp while doing some aggressive (bar held right above the white dotted line) regen braking and see if their ICE fires up and then shuts right back off, I would appreciate it. I'd like to put this baby to bed for good.

Otherwise, I gotta go in the shop and have them check her out. She only has 6k miles since purchased last January. Oh Covid! lol

 

It's always happened with 4-6 bars. I've never maxed the charge since I've owned it. It's happened on hot days, cool days, cold days, with AC/Heat on/off, day/night, soon after first start of the day, and after having been driven for quite a while.

I think it's time I get it checked out. Hopefully they take me seriously. There are no engine warning lights so...

 

It happened shortly after the ICE did its warmup today. I was driving on ICE from a light, then I released the gas to reenter electric. Then as I approached another light and was regen/braking the motor flashed on and off.

It always happens when I'm regen/braking (usually maxing out regen at white-dotted line) and it doesn't matter if the motor was running very recently or not.

When I notice this on the highway heading down off-ramps, I'm usually previously cycling back and forth - several miles on battery, then I engage the ICE over hills to maintain speed.

Does the battery heat up while I'm regen-braking? Even if I'm only doing it for like 10-15 seconds? With only 4 or 5 bars?

Never am I in a situation where I have a long hill and am regenerating for miles and miles. This is Kansas remember? And I don't think I have ever had the motor flash on when I'm just letting the car decelerate without added brake-regen. In fact, I can safely say THE ONLY time this has happened is during depression of the brake with the ICE off for an indeterminant amount of time (anywhere from 15 seconds to a couple minutes prior to braking).

And this happens in all weather conditions.

Again, when this happens my brake sensitivity and effectiveness changes noticeably. I'm assuming THIS is normal? It's really weird and feels mechanically counterintuitive.

 

It does it regardless if the heater or AC is on - or nothing at all. And when it does come on it just "flashes" on and off. I can't imagine that would have much of an effect on anything. I literally feel the little jolt, watch my split gauge MPG drop, and then the motor turns right back off and the MPG goes back to 100. All under a second.

 

Here's an update on my issue:

I went to the dealership and had them look the car over. They found nothing of course (no warning lights no problemo). So I asked to see the shop foreman and took him for a drive (masks on and windows down). He had me switch the car through the various power modes and I was able to demonstrate the oddity on multiple occasions. He said he would call the tech helpdesk. After a week or so I called back and was told the behavior is normal. I wasn't convinced.

I also test drove a 2021 Prius but wasn't able to get the split screen up so I couldn't ascertain when the ICE was turning on. Nice car though. I need to test drive a used 2019 next, if I can't get one of you guys to crack my case.

Here are some videos of the behavior happening. In all situations I can hear the motor running when the split-screen MPG meter drops down from 100 (so I know it's not just a graphical glitch). Occasionally the motor will continue to run for a bit, but most of the time it turns on and then turns right back off about the same time I come to a stop or shortly thereafter.

(this one has music accompaniment)

See if any of ya'll can mimic my issue. Car is warm, the rest of the info is in the videos.

Thanks in advance!