B gear?

READ YOUR MANUAL....
There is NO one pedal operation in a Prius. It's the same as the 2018 Prime that you had. It's used to slow the car on long downhill decent, just like any other car. Guessing on how a car operates, places yourself and everyone around you in danger.

Sorry for the rant....

 

Of course there is some controversy about this, but the B gear is meant as an engine brake. This was deemed necessary, because the Prius engine does not create engine drag when it's not engaged. On newer models the engine does engage, but the B function is still available.

Although rare, there could be a situation where regenerative braking is not available because the hybrid battery is at full charge. This results in the car picking up more and more speed on a long descent, to the point of danger, not unlike an 18 wheeler with brakes burned out, unable to slow down. It happens. I assume that Toyota didn't want to be responsible for such an incident with a Prius, so the B engine brake was provided.

I have tested this myself, and when the hybrid battery is fully charged, there is no regenerative braking. The result is that the car picks up excessive speed on the downslope. Friction brakes are sometimes not enough, and using them can result in excessive wear, and even brake loss.

The energy of the moving car must be dissipated somehow, and since regeneration and friction may not be available, the B position, engine braking is there to dissipate energy as heat by manipulating valve timing to achieve some amount of engine braking.

Of course some will disagree, but that's what my research and experience tells me.

 

even the bz4x doesn't have opd, unless they've added it since i looked.
ignore b gear, it'll go away eventually

 

try it when descending the grapevine...

 

In the MID there is a setting where you can change the level of regen between 1-3. I think level 3 is more than enough to achieve a one pedal type mode. If you need more than what the regen can provide you just add it in with the brake pedal. It'll slow you down to around 5 or 6 mph then you need to use the brake pedal to bring you to a stop. And like Paul G said a full battery won't provide much regen so plan accordingly.

 

And that's how it is 99% of the time, but you know how companies are about potential liability.

 

BAD ADVICE; If you want to drive a Tesla, drive a Tesla - because I don't want you to rear-end me!!

 

You can still use the brakes while in B mode. You're just engaging a more aggressive regen when you lift off the accelerator when you use B mode. So in B mode, if you don't need heavy braking, you can slow down just by lifting off the gas pedal. And if you need more than what regen is providing add in some brake pedal to achieve the amount of braking you need.

 

Even braking in D the car is using regen to do slow the car. You can see that on the power meter in the MID.

 

The OP used to drive a Tesla and apparently in one pedal mode.
Different cars, different operating principals - NO one-pedal operations in a Prius!!!!!
They're going to let go of the pedal and expect the car to STOP; We both KNOW the Prius WON'T STOP without applying the BRAKES!

That's the entire point of this thread; since the OP doesn't know how the car is suppose to operate, making them think it will operate like their old Tesla is dangerous at best.......

 

Perhaps calling it lift off regen above 6 mph mode is more appropriate then to avoid confusion.

 

Toyota programmed early and non-plugin Prius models so the deceleration behavior you feel in B is like a conventional car downshifted to a lower gear. You should notice that the car slows a bit more when you lift off the go pedal than it does in D. (Unlike a downshifted conventional car, B makes no difference when you're accelerating.)

Note that, just like a conventional car downshifted, this is not a "one-pedal drive" mode. While the car at cruising speed will slow more markedly in B when you lift your foot off, it will not come to a full stop, but end up moving forward at a creep speed like any other conventional car.

To make a full stop, you sooner or later have to use the brake.

Given that you have a 2025 Prius Plug-In, you are not limited to just one preprogrammed slowing effect in B mode: you can select Low (the default), Medium, or High, as described in your owners' manual under "Regeneration Boost". Here is that excerpt, uploaded to PriusChat a while back by someone else.

Even when you set it to Medium or High, it still won't be one-pedal drive. It will slow more markedly from speed when you lift off the pedal, but it won't come to a full stop unless you brake.

It successfully does what it's built to do, but one-pedal driving isn't what it's built to do.

In non-plugin Prius models (which have small battery capacity), it is built to let you take long steep downhills in a way that puts less stress on the battery. There's no other compelling reason to use it, in a non-plugin.

In plug-in/Prime models, which have a large battery capacity, you might use it in a wider range of circumstances, and try different settings of the regen level. But it won't give you one-pedal driving, and isn't likely to improve your MPG.


Technical details

The letter B should remind you of an engine-braking effect such as you'd feel by downshifting in a conventional car to slow down without use of the brakes. A Prius, though, has two ways of slowing down without use of the brakes: engine braking and regen into the battery. The car picks the combination it'll use to slow you down: driving in B doesn't mean it must use engine braking, and driving in D doesn't mean it can't use engine braking. Whether you're in D or B, the car has the same capabilities and will use them as appropriate.

The "Regeneration Boost" feature appearing in the gen 5 Primes/plug-ins can be seen as a sort of punning use of the same letter B.

Technical misconceptions

If you have been on PriusChat for a while, you may recognize the above from the many times Paul has posted it elsewhere. The bit about the engine not creating drag when it's not 'engaged' is a bit beside the point, because nothing in the Prius transmission ever disengages. The engine can be at 0 RPM whenever the car wants it to be, and of course it produces no drag then, but the car will also twirl it at up to 5,000 RPM, enough to dissipate around 11 kilowatts of power, and that also happens whenever the car wants it to. There's no extra step where anything has to 'engage' first. The car slows the counterrotation of MG1 and the engine RPM perfectly follows. This isn't something unique to newer models.

Frequent readers will also recognize this from Paul's previous posts. Paul seems to doubt that the car ever chooses engine braking on its own except when the driver has selected B. Some of the reason could be that Paul drives a Prime, whose much larger battery will rarely ever be charged enough on deceleration to trigger the car's use of engine braking in D. Two different times last summer, Paul set out to test the question, but neither time produced a result either way, simply because his battery didn't reach full-enough charge on either descent.

At some time later than those two attempts, Paul began writing that he has indeed run tests that confirmed his belief. (More at the link above.) But, if he is referring to any tests he conducted later after the two inconclusive ones, he's never offered any details of such later tests.

None of which is to say he wouldn't be welcome to post such results. We might learn something from finding explanations of him getting results that differ from what others get.

Paul has also repeatedly made this claim that the Prius gasoline engine uses valve timing manipulations to achieve engine braking—a confusion with the way Jacobs braking works on diesel-engine rigs.

On one occasion earlier this year, when advised of that confusion, Paul responded in an interesting way: by posting text from a Cummins Diesel page about Jacobs braking as if it had come from a Wikibooks page about the Prius instead.

Readers less familiar with Paul's posting history on this topic deserve to know at least that much about it (and can follow the links to see more if desired).

He tends to describe his position as simply questioning a 'consensus' among other PriusChat members about how B mode works. Which, ok, as long as one sees that what he calls the 'consensus' involves many other Prius owners who have tested the behavior themselves and often documented it, including with instruments and whose experience doesn't match what he claims.

 

Of course none of that is supported by evidence.

 

Jeepers Paul...do you always disagree with everything? Sure seems that way sometimes!

On ALL Prius vehicles I have driven ( Gen3 liftback, Gen3 Prius V wagon, first gen Prius plugin, Prius C ), when the car deems the battery "full", it automatically engages "engine braking mode". It doesn't matter if the shifter is in "D" mode or "B" mode. It obviously takes longer to achieve this with the first gen Prius Plugin because the battery is larger, but it is MUCH smaller than the batteries in the "prime" models. "Engine braking mode" exists to protect the battery from "overcharging", and the car will take action by itself to achieve that.

I can't speak to the Gen4/Gen5 models, but from reading around over the years, they seem to operate exactly the same way.

 

They totally do. Any time you lift off the go pedal and you feel the car slow down without the engine revs going up, regen braking is what's happening. Same when you use the brake pedal lightly and you feel the car slow down without the engine revs going up. (If the engine revs do go up, the car has chosen to do some engine braking as well, which it will do when the battery is so charged there's little capacity left for regen charging. When there's no capacity left for battery charging, then only engine braking is used and the engine revs go up. If you're on the brake pedal, of course actual friction brakes come into play too.)

So the difference you're noticing between the Prius and the Tesla comes down to a designer's choice for how the car should feel to drive. Toyota chose to make the Prius drive like other cars, where it goes when you press the go pedal, slows down when you lift off, but doesn't completely stop unless you brake.

Tesla decided to offer a mode that isn't like what other cars do, so it takes getting used to as you said, but maybe you like it when you get used to it.

The difference isn't whether the cars can or can't do regen, it's about what user interface they were programmed to offer.

 

The battery is the limiting factor when it comes to regen braking and one pedal driving. Individual cells can only take in so high a charge rate before potential harm to the battery. Hybrid batteries are simply too small to do more than moderate braking, and can't pull off one pedal driving with it.

The battery in a long range plug in, and resistor bank in a locomotive, is large enough to provide moderate braking and one pedal(handle) driving. For a shorter range BEV and most PHEVs, that may or may not be the case. Comes down to the battery size and what braking force the vehicle needs.

Note, Teslas use blended braking with one pedal driving to maintain a consistent leveling of braking even when the battery is near full.

 

Even the hybrid battery can give you quite strong regen deceleration (when it has capacity); you feel this when you press the brake pedal.

Using the brake pedal will give you much stronger deceleration than you feel just from lifting your foot off the go pedal, and the car still can be using regen to do that (down to the single-digit speeds where the friction brakes have to take over).

The fact that you don't feel that level of regen just by lifting your foot from the go pedal doesn't reflect a limit in the car's capability. It reflects a choice by the designers to have the feeling of lifting your foot from the go pedal be like the same feeling in a conventional car. So it is programmed to give the amount of slowing you normally get from a normal car's drivetrain with no gas, and in B it's programmed for the amount of slowing you get in a normal car's drivetrain in a lower gear with no gas.

To have it act like one-pedal driving would just require different programming. It would have to blend regen, engine braking, and friction braking in order to be one-pedal all the way down to a stop. The car can already do all of those things; it just isn't programmed to do them under control of one pedal.

 

You could have one pedal operation in an ICE car. It just isn't practical for the same reason Toyota warns against using B too much, it would be inefficient for most people. A hybrid's battery is small enough that the heavy braking of one pedal driving will keep it charged up, leading to a one pedal ICE car much of the time.

The charging C rate is likely of more concern. A Prius hybrid and PHV need roughly the same amount of braking force at a given speed, generating about the same amount of regen energy. The PHV cells will see a lower C rate, since there is more of them to divide that energy to, leading to less 'wear and tear' on the battery.

Tesla only blends the brakes so the driver has the same braking feel regardless of the charge level. That can be turned off if the driver likes dealing with less braking with one pedal while the battery is near full. Their cars, and other EVs with one pedal, can bring the car to a complete stop with regen alone, only engaging the friction brakes to prevent rolling once stopped. The generally more powerful motors play a part, but they need bigger batteries to support those motors.

Yes, the Prius designers chose to have the car operate in the manner of a traditional car, but there are limitations in a noplug hybrid that keep it from operating completely like a BEV.