We use the EV mode when going home for last quarter mile because its mostly downhill so for fun have the electric motor tow us home. What is "quirky" about this mode is sometimes EV won't engage even if big battery is full, gas engine is warmed up. We know that going faster than 25mph cancels the EV and that short trips prevent EV from engaging. Other times EV just cancel citing excessive speed when we are going 10-15mph. So this is no problem but wondered if anyone knows what the parameters are for EV engaging and dis-engaging.
It can take quite a long time for the car to be in its full "warmed-up" state, especially in winter; both because it's cold outside, and because you're drawing heat from the engine to warm the cabin. There are other parameters too, like if the HV battery is too hot or too cold. I'm not sure anybody but Toyota has a full list of exactly what the parameters are. A rough approximation of the warm-up stages is in this thread. I would disagree with some of the statements there, but it's probably the most accurate compendium I've seen. (For example, "if the coolant temperature is above 60C on power up, Prius is already in [S4]" - this may be the case if you stop and quickly restart it, but I (and I'm sure others) have noticed the engine running for long periods while the car is well over even 80°C due only to a recent warm restart.) The manual gives a list of some of the reasons they have; perhaps the least obvious one is if the windshield defogger is in use.
i used to get this in my gen II's, come off a long highway trip in summer, full green battery, creeping around back roads at 10 mph and the engine running the whole way. no idea why.
