Previously I have noted that sometimes the MFD will show the motor as not being on when I can hear it starting and running: Motor runs but does not show up on MFD? | PriusChat I have also previously noted that sometimes when the car stops the wheels on the display are shown turning for quite a while while the real ones are not - as the car is not moving. Today we went to a toxic waste drop off. This involved crawling around a parking lot, moving one car length at a time, for 40 minutes or so, following a previous 40 minutes doing the same thing on a city street just to get into the event. Naturally this drained the HV pack down to two pink bars. (Annoyingly the car isn't bright enough to realize what is going on and let the ICE run long enough to charge up the pack. Instead at that charge point it starts the ICE for every move, then shuts it right down again.) Anyway, while it was in this state, I noticed that at most stops the display was showing power going from the pack to the electric motor. Put it into park and all the arrows instantly went away. Put it back into drive and they returned. Press harder on the brake, much harder than I normally would to remain still on flat ground, and once again the arrows disappear. My hypothesis is that with brake pressure that is light the car tries to get the car to crawl by sending power from the pack to the electric motors, but the physical brakes hold. Press harder on the brakes and then it decides that the driver doesn't want to move and doesn't send power. If this is correct then the current should show up in Techstream. I felt that the amount of brake pressure needed to cancel the power transfer shown in the display was excessive, corresponding more to what I might use while holding the car on a significant grade, and overkill for keeping it still on the flat. (Not just this car, any car.) It crosses my mind that this might be something which needs to be calibrated, and it is out of calibration. Either because the car needs to go through a relearning procedure of some kind, or because the brake position sensor isn't sending the right information. Note, even though it was a fairly hot day (around 85F outside at the time) neither the AC nor the fan were on, we had all the windows down instead.
That is what it does. Whether the pedal pressure threshold is too high in yours is a question I can't answer, and seems maybe like a matter of personal taste. I like making very gentle stops, so usually my brake pedal pressure is quite light at the moment the car comes to a stop. Then, once it's no longer moving, I press harder and hold, so the drive torque cuts off. It's long-ingrained habit by now.
Seems counter intuitive to me. The car came to a stop with 3 psi on the brake pedal but once stopped (so no more KE to burn off) it now needs 6 psi. Sort of the backwards Bizarro world version of "an object in motion tends to stay in motion". A traditional automatic transmission ICE vehicle will crawl at a couple of miles per hour whenever the motor is on if the brake is not applied (or the car not aimed up a steep hill) because when in gear even idle transmits a little power through the torque converter. On an EV, or a hybrid in EV mode like the Prius under these conditions, why would the car try to turn the wheels at all when there is pressure on the brakes and none on the accelerator? It could be set to crawl at 0.5 mph (or similar) with no pressure on either pedal if in drive, and work up from there with accelerator pressure. That's 1/6th normal walking speed which is very slow - I don't think I can regulate velocity on this or any other car well at speeds less than that. Looks like Mazda's i-Stop works a lot like the Prius though - it won't turn off the motor when there is light pressure on the brake even if the car is fully stopped.
Because the design decision Toyota made early on was for it to feel a lot like that "traditional automatic transmission ICE vehicle" so it wouldn't be unfamiliar to people. That traditional vehicle won't just crawl "whenever the motor is on if the brake is not applied"—it starts crawling as soon as your brake pedal pressure is light enough for that engine-idle torque to overcome it. If the Prius waited for you to be fully off the brake before applying any torque, that would feel different and weird. The main difference is, the engine idle torque in the traditional vehicle never cuts off: even while you're sitting there with the brake pressed hard enough to remain stationary, the transmission is still applying torque, meaning engine power being burned off as heated transmission fluid in the torque converter the whole time. At least in the Prius that waste of energy ceases as soon as the car decides you're holding the brake hard enough that no "crawl" simulation is needed.
