ICE turns on inexplicably

You don't have the real-time indicator on the display by the speedometer? That thing is really helpful if you're hyper-miling. If you turn on split screen mode for the main display, you can select the current consumption which will show mpg in HV and m/kWh in EV (the middle two illustrations below).

 

I do, but that thing is all over the place every instant. When pulling away from a stoplight or pulsing it's like 2 mi/kWh, and when cruising it's pegged at 10+. I have no way of knowing the average. I use the HSI 99% for hypermiling.

 

[CITATION="Vitrail, poste: 3144256, membre: 192240"] Avez-vous une idée de la raison pour laquelle il fait cela? [/CITATION]
J’ai constaté exactement la même chose : Si on démarre en altitude avec la batterie pleine charge le thermique démarre dans la descente qui suit.
C’est impossible à éviter.
Grace à l’application Hybride Assistant j’ai eu l’explication dans le rapport HR généré.
C’est une sécurité contre la surcharge de la batterie propre à Totota je suppose...?
Voici ce qui se passe sur le plan électrique :
Quand la batterie est à pleine charge le SOC est à son maximum et le CCL ( Charge Control Limit ) est au minimum environ 10Kwh.
Dès que l’intensité du courant de charge ( visible avec la courbe de charge ) vient toucher la courbe du CCL le thermique démarre pour servir de frein moteur dans la descente car le freinage électrique n’est plus possible. Au plus fort de la descente le moteur monte à plus de 2000 RPM
Le seul inconvénient que je vois à ce système est que le débit d essence n’est pas coupé et que l’on consomme inutilement du carburant.
J’ai souvent constaté que sur une descente de 10 km avant d’arriver sur le plat l’ODB m’indique une consommation de 0,3 l./100 km.
J’avais exactement la même chose avec ma précédente P3 PI mais la consommation d'essence était plus élevée.

 

Actually, just today my Prime has decided to turn on the ICE while going downhill with 70% battery… (I have made another thread about it, before finding this one)
Thus, there was still plenty of battery to fill with regen energy before the ICE needed to kick in to work as a air compressor to dissipate the energy.
Otherwise said, the ICE in my case turned on for no apparent reason at all. It wasn’t cold, there was plenty of charge left and plenty empty to fill it with regen, it wasn’t particularly cold (50F) and the car was in not super cold garage. I have done the same roads in the same way with the same AC settings, purely on EV mode. But today and a couple of days ago, she decides for no reason to turn on the ICE…

 

It is probably because the SOC rises to well over 100%, possibly around 110%, and the hybrid system is entirely isolating the traction battery to prevent damage.

What is the elevation change? The SOC rise in percentage equals to the altitude drop in feet divided by 50. So, if you are descending 500 ft, the SOC rises by 10%. You are probably around 97% SOC when you come to the top of the hill, and it could be that you reach about 105% SOC at the bottom of the hill, which results in an EV-mode shutdown.

 

How long and how strong were you regenerating? The only time something like that happened to me (Living in FL, I don't get to go down many long, steep grades.) was coming down from Grand Mesa on our last trip to Colorado. The ICE came on at 98% after starting the descent at about 10%. My guess is that it hit a temperature limit.

But as the manual mentions, the ICE can come on for other reasons that it doesn't list. There's a certain amount of mystery to the whole thing.

 

Maybe 10 secs and very mild braking. Nothing major. And nothing to have the battery jump from 70% to 100% in less than 1 min...and requiring "cooling off the battery (by turning the ICE on, with a battery not yet full?)" or using the ICE as a compressor to dissipate the braking energy.

I am used to the Prius Prime or Gen4/Gen3 (I have owned/own all 3 of them now) running the ICE because the battery is full while needing to continue to brake (i.e., when going down a very long downhill slope). This is nothing like it. It really seems to have turned on for just *no reason*. Bringing me to wonder if there is something wrong/broken.

It is my 3rd Prius in a total of 13 years of Prius ownership, so I have some experience of how "the Prius behaves." I don't say lightly "turned the ICE for no reason".
I have driven all 3 of them down really steep long hills, and yes, that's when I expect the ICE to turn on "for good reason." This was a "no good reason" situation, in which it turned the ICE on. So much so, that I ended up here in Priuschat asking "what is going on, and why?"
(the question, I have to say, remains unanswered)

 

I agree. I don't see a reason either and we both have considerable time with various Prius generations. And you have more experience than I do in the mountains with a Prime.

I guess you could take it to the dealer, but without any trouble codes, I think they'll probably tell you not to worry about it.