Hi all, I recently changed my commute and noticed that my 2023 Prime would consistently start its gas engine for a brief period while in EV mode. This happens near the start of my commute, during a maybe half mile downhill stretch. There's a stop light about halfway down the slope - if it hits red and I stop, the car tends to stay in EV mode. However, if I hit a green and coast on through, the gas engine will almost certainly turn on by the last quarter of that stretch. During this time: I'm mostly coasting downhill between 35-40 MPH, not accelerating while lightly holding on the brakes. The energy meter is usually showing partially charging. I'm within the first 5 minutes of my commute, starting with a fully charged traction battery and having driven a few blocks on flat roads - the EV range still shows the full estimate more or less. The car has been parked covered and not in direct sunlight. When I notice the gas engine turn on, the dash indicator still shows I'm in EV mode, but the second icon showing it's using EV range disappears. After the downhill portion I merge onto a freeway, and the car turns off the gas engine and reverts back to EV mode within minutes - maybe less than a mile is driven on the gas engine. Looking at the owner's manual, section 2-1 (page 79), the only thing I'm seeing that might apply is that the gas engine might be used "When the temperature of the hybrid system is high. The vehicle has been left in the sun, driven on a hill, driven at high speeds, etc" Surely coasting downhill on regen doesn't get the hybrid system hotter than actually driving at highway speeds up and down hills - which happens in the latter part of the commute and the car stays in EV mode the whole time. The manual is frustratingly vague about how it actually decides to swap modes. Is there too much regen going on with a full battery? Does anyone have an idea if this makes sense/tracks? It's pretty annoying to have the gas engine kick in then turn itself on, inefficiently eat some gas, then turn off before it even properly warms up. Maybe someone with some technical know-how can tell me if there's a way to avoid this? Thanks for reading!
if you start with a full charge, the car has no alternative but to use engine resistance to burn off the extra regen. it spins the engine with the extra electricity, without injecting any gasoline.
I have the same issue with a long downhill run after leaving home. I believe the issue is that the battery is fully charged and can’t take any regen charge. There’s a couple of things that you can try. I have found pre-warming the car, using the phone app, helps, even when plugged in. Or you can try coasting in neutral down part of the hill. Coasting has the advantage of keeping the brakes disks free from rust.
It definitely does consume some gasoline, as the gas mileage indicator goes down by a mile or two each time this happens. I didn't pay for the remote start, and but I'll give neutral a try on a less busy day.
I have noticed this too on regular routes. I have also noticed using an OBD app that is uses a very small amount of gas like hundredths of a gallon. My best guess is that it has something to do with circulating oil, coolant or fuel.
Welp coasting downhill in neutral is apparently a traffic violation in California so I'll avoid doing that. I guess I'll just need to eat the inefficiency since there's no built in way to only charge to 90-95% of usable capacity. Thanks all for confirming this isn't abnormal behavior at least.
I generally leave at the same time M-F, but post-commute travel varies abit, so I can have anywhere between 0-20% remaining EV range when I plug in to charge at night. Gen 5 also doesn't have an option to charge to full by x time, so kinda would have to finagle the start and end times to guesstimate it.
yes, it would take some experimenting. only worth it if you really want the engine to stay off. might be a good idea just to try the route with less than a full battery first
Pay for remote start? The Toyota phone app includes remote starting in Canada. Maybe it does expire at some point.
In the US it came with 1-year remote connect, which is required for remote start. Mine expired and I am not interested in paying for it since I found it to not be all that useful - it's never cold or hot enough that I need feel I need to get climate control going before I get in.
I just checked and my subscription here in Canada is free for 3 years. After that they want $10 per month plus tax! Hopefully it comes down in price or becomes free by the time mine expires. It is useful and I think it also warms up the battery before driving. But… No way I am going to pay that much for a remote start!
It is freewheeling the electric motor since it cannot use regenerative braking with a full battery. For some reason, it also likes to turn on the engine. It could be to adjust the engine rpm with the freewheeling and engine braking going on at the same time coupled through the transmission. If you are charging the Prius PHEV overnight, you should always use the charge schedule to reduce battery degradation. Charge to a lower SOC (like 80–90%) just before you drive, which you can accomplish by charge schedule. That will solve your engine-running problem. Keeping the battery at 100% all night is not good for it anyway.
This issue keeps happening in my regular commute area as well. I’ve tested several different situations, but the result is always the same — whenever there’s a continuous downhill stretch of 1–2 km, the gas engine will kick in to burn off the energy from regeneration: Regardless of whether it’s in D or B mode Regardless of which regeneration level is selected Regardless of whether the main battery is full The only effective way I’ve found to prevent the gas engine from activating is to occasionally press the accelerator slightly during a long downhill, to interrupt continuous regeneration. But honestly, I still find this logic pretty strange. I’d like to ask the manufacturer at some point if there’s a different firmware version that could improve this behavior.
Regenerative boost and B mode do not increase the maximum regenerative power. They only modify the brake- and gas-pedal response. B mode can turn on engine braking though. Surprised it happens even when the battery is not full. There wouldn't be a firmware update.
The peak regen rate is very high, compared to the wall charge rate. I suspect the system is prepared to do that short-term, but not long-term, as part of its general battery babying strategy. Maybe also heat dissipation issues in the inverter bits. With the non-plugin, you'd run out of battery capacity quite rapidly, so you might never see that long-term limit kick-in.
Also, you can’t fast-charge the battery if the SOC is over 80% or so. Try it at 70% SOC and see what happens.
How do you know that is the purpose? It could also be that going down hill interrupts or interferes with engine oil lubrication. One route I drive pretty consistently activates the same sequence. Coasting down hill using very little energy or fuel for a mile followed by a flat section of road which then goes into a slight incline for about a half mile. Even when using predictive efficient drive I observe the engine start almost alway at the same spot. Some of things I have observed on my OBD app: 1. The amount of gas consumed can be less than a tenth of a gallon. 2. The battery charge state which reads 90% when charging is complete is not close to being 100% 3. The charge state does not significantly change when the gas engine briefly cycles on/off I looked into what PIDs I could add to my app dashboard to see if I could more precisely determine what is different before and after the gas engine runs for the short time period. The only PIDS I I see that might help are Engine Coolant Temperature and Engine Oil Temperature. If anyone has any other ideas of which SAE PIDS might be helpful to determine the purpose of this short engine run cycle please let me know.
