Drive modes

There is no issue with changing modes in flight.

 

The Prius is essentially computer control. You cannot harm the drive train in any way, unless you smash it yourself into a wall.

You can floor it at will (rpm is limited by the computer - and that's cool because you get access to all the power the drivetrain can deliver, immediately without need to change gears or whatever - the computer takes care of that revving up how it wants in the best way possible with no harm), you can change drive mode as often and how many times you wish when you want, and you can even push the P button while on the highway, it will simply refuse to work - the computer will complain with a beep.

Even changing "gears", that is between D/B/R/N is computer controlled and foolproof. There are some clear conditions by which you simply cannot change as you wish exactly to prevent any harm.

Essentially drive it as you like, if you do something wrong, it will beep and write something in the display. You will not destroy anything.

The user's manual is full of warnings for everything, but for the operating modes, there is nothing because there is nothing to break. The only way to break it, is to drive it in another car or a wall....

 

If there was some obscure bit of info that was not being disclosed, and it was leading to disastrous damage, Toyota would have a BIG problem.

 

One minor 'gotcha' that should never come up but I will caution you about just because. Above 40 something in Gen1 and 2 and 60 something in Gen3 and 4 the engine MUST run to prevent damage to Motor/Generator 1.
When in N, the engine never starts if it is off, and never stops if it is on.

So if you were at low speed in N with the engine off, and sped up a great deal to exceed the limits above, the car could not protect itself. I can envision no scenario where it would be a good idea to be racing down a mountain in N anyway, but don't, as it may damage ($5000) the transmission.

 

A small correction:
For the Gen 3, the engine will always be on at speeds over 46mph. Even shifting into N I was never able to get it to be off (RPM=0 on the Scangauge) at speeds >46mph. Because I don't have the car any more, I can't test whether the engine would stay off if you got the engine to shut off at <46mph at the top of a big hill, shifted into neutral, and coasted to speeds >46mph.

For the Gen 4, the engine can be off (RPM=0) at speeds of at least 68-70mph. Testing it at higher speeds is very difficult because the battery doesn't provide enough power to go any faster anyway.

 

many topics here:

The worry about over revving the M/G1, has more to do with how steep the hill is than with how long it is.

B mode (which is less efficient by design) help on a long descent, throwing away energy by using the engine as an air pump, slowing how quickly the battery fills. This keeps the battery cooler, the disc brakes cooler, and adds wear to the engine. (It also makes the engine make more noise the harder you hit the brakes, which is non-intuitive) That trade off is yours to make, but overheating the battery and especially the brakes have some negative impacts.

I recommend B mode from the top of any downhill over 1000 feet tall.

I hardly ever recommend N at all*, as it does not charge the big battery while in N, but it is only a danger to the transmission down steep hills in N. (Toyota is required by law to have a B mode and an N mode, you are never required to use them. Few Prius owners ever need either of them. They shift only out of boredom and a desire to feel they are 'helping')

*If your brake rotors seem rusty because you always use regen, you can put the car in N and stop from highway speeds once. That will remove the rust from the rotors)

 

The car will tell you when you're not supposed to do something that's bad for the car. It won't let you.

 

I use N only at the car wash.
B each time I go downhill to prevent the metal brakes to overheat. The Prius already goes BTW already into "preservation mode" if the battery is fully charged, by using the ICE as an air pump even in D if you are going down hill and not braking - essentially it doesn't know where to put the energy because the battery is full, and hence simply wastes it in heat. (which is BTW what all regular cars do when you release the accelerator pedal, don't brake, leave the gear and they don't have any recuperation, apart the small alternator...).

 

And, the drive modes (ECO, Normal, and PWR) are merely accelerator pedal sensitivity settings (although ECO also changes some heating and air conditioning settings to run in a more efficient mode, but you can do that yourself by hitting the ECO Heat/Cool button), there's no reason why you couldn't change them on the fly. ECO reduces sensitivity so you can more carefully adjust the power, Normal is linear, and PWR makes it so that less pedal input is required to get moderate power. However, this only affects approximately the first half of pedal travel, past that, it doesn't matter what drive mode you're in.

 

I used to use N all the time on downhills on the highway in my Gen 3. According to my Scangauge, the fuel flow (GPH) dropped by about half by doing this (and the MPG correspondingly doubled). I would leave the car in "D" on these downhills only if the the battery needed regeneration. The downside of leaving it in D was of course that the car lost speed more quickly if the downhill was not very steep.

In the Gen 4 I don't bother to put it in N on downhills because it will go into EV at highway speeds.

 

I had the same concern. I swear I saw it mentioned in the Owners Manual, but now I can't locate it.

I've changed my "Drive Mode" many times while underway and it works fine. Even while going 70 mph, changing from "Normal" to "Eco" with no warnings and no problems.

Here's something interesting on page 321 of the Owners Manual. Regarding the Drive Modes...

Power Mode: "Suitable for when *crisp handling* and enhanced accelerator response are desired, such as when driving on mountainous roads." (Crisp handling??? That makes me think it changes the suspension, which we all know it doesn't.)

Eco drive mode: "Suitable for driving that improves fuel economy by *generating torque* in response to accelerator pedal operations more smoothly than in normal mode." (and when the AC is being used, the AC automatically switches to Eco mode.)

(And on page 669, I found it mentions a "Low 12-Volt Battery" warning that will pop up. Your shift position lever may not operate if the 12-Volt is weak. Somebody in another thread was asking it there is a Low Battery warning.)

 

The only thing I could think of is... Does the Prius have an electronic differential lock, activated by applying the brake on the inside front wheel, to prevent wheelspin? Could that be enabled or made more aggressive/active at higher speeds in PWR?

That's the only way I could see PWR even possibly sharpening handling.