Has anyone ever had a problem while using the hill break? My 06 prius recenlty started reving up really fast for no apparent reason? I switch back into Drive, fearing a mechanical problem.

Any advise would be welcomed

If you put it to "B", it's equivalent to putting a conventional transmission into a Lower gear (1st or 2nd gear depending on speed) to create engine resistance or "engine braking"; by keeping the engine's revs up, it uses the engine's compression to create resistence to help slow the car down without using the brakes (all this is done with your foot off the gas pedal BTW).
the downside is? engines are not normally used to slow the car down, that's the brake's job or in the prius' case, the generator/electric braking and the brake pads themselves, therefore, in the long run this can lower your compression ratio thus reducing your engine efficiency and power output.

In other words, brakes are for stopping/slowing, engine is for moving

Just keep it in "D".

hope this makes sense,
if not , please dont hesitate to ask

gj

How does it lower the compression ratio?

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

over time, wear and tear gradually comes in, and for a person who consistently uses engine braking, this can speed that up.
Now, this may not apply to those who change their oil very regularly or religiously. But IMO it can happen. I know if you ask out there, you'll get a mixed crowd of people saying "it wont" and "it will". I was always taught that "it will". therefore, i like to keep it simple and use brakes for stopping and engine for moving. It's cheaper to replace brake pads than to overhaul an engine.

With the old carborated engines, the problem was gas could wash or dilute the oil leading to excessive wear on the rings. I suspect the Prius ICE has solved that problem by turning off the injectors and better igniters BUT if the air is unburned, it could lower the catalytic converter temperature. . . . Certainly something to look at.

Bob Wilson

Operation Iraqi Oil Freedom:

Automatic, stock, project car.

My other 1500 cc car:

Automatic, stock, backup car.
Free speech, dialog and knowledge thrives without the poison of SPAM.

Prius B mode is a substitute for a traditional transmission lower gear, which would use regular engine compression to slow the vehicle.

B mode is not unsafe for the vehicle and is nothing like using engine compression for braking, as in a conventional vehicle, because the engine becomes nothing more than an air compressor.

In large road going semis, a Jacob's brake is an engine compression brake which suspends fuel to banks of cylinders, usually in pairs of 2, and uses the natural compression of the engine to help control speed and ease braking. It is very effective and it not damaging at all to the engine. Drivers of these vehicles uses these brakes on some very long downhill stretches for miles and miles.

In much the same way, the Prius suspends spark and fuel when in B mode and the ICE becomes nothing more than a sophisticated air compressor.

Please use B mode as you see fit with no concern over ICE longevity or wear and tear. B mode is there for you to use at your discretion.

It has been said:
Hybrid drivers come in 3 flavors, greenie, techie and cheapie. Pick any 2.
2005 Prius, Melinium Silver over gray, package 5 (AI)

I suspect that you experienced the following: You used the "B" setting to coast down a fairly long hill, long enough to charge your hybrid battery fully (all green bars). At that point, the hybrid system needs a way to shed the extra and unneeded charge, so it spools up the internal combustion engine to do that. No harm is done; the hybrid system is designed to handle it. That, at least, is what I have read elsewhere. I have experienced this revving myself under similar circumstances.

highroute -
2006 Barcelona Red Metallic

I have had the same condition in my FEH. I salivate, because that means the next time I want EV mode, I'll have a full battery.

-Charlie...