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  1. #1


    Has anyone talked with their service center about the loud noise, if you experience it, which comes on about half way down a long hill, when using the engine breaking?

    I know the manual warns there will be a noise, but in the last week since I started using it regularly, we're near the end of our first month with the 06, the noise seems to be getting louder?

    I'm wondering if we're increasing the life of the brake pads and whatever, while shortening the engine life?


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  3. #2


    I had asked our dealer this, as we live on a nasty little mountain, and he said he had not heard of any damage caused by daily usage of the breaking gear.

    Has anyone been advised differently?

    Just remember to shift back to drive after the hill,
    and not to R !!!

  4. #3


    We started noticing what we thought was a sudden racing of engine after a minute or so in engine braking gear, near the bottom of the hill we drive often.

    So we stopped using engine braking.

    But I've spoken with a neighbor who commutes over the same hill, and she gets same result and says her dealer says it is perfectly normal, and to check the owner's manual instructions on it.

    I haven't re-read the manual on the topic, because I trust my neighbor.

  5. #4


    Do all hybrid cars have conventional braking (disc or drum) in addition to the ability to use regenerative braking/

  6. #5


    Yes, all hybrids have standard brakes in addition to the regenerative braking. The CV (Constant Velocity) transmission (planetary gear set) smoothly changes the electric motor into a generator by slowing it down and then spinning it in the opposite direction causing resistance to forward motion ... you still need the normal brakes if this is not enough.

    On the Prius, not sure about the others, there is a 'B' (braking) select on the shifter in addition to 'D' and 'R' ... 'P' for park is another button. Anyway, the B makes it so you are running purely on the gas engine and generally the manual talks about using this for engine braking. I've never used it because brake parts are relatively cheap and I had a bad experience with my first vehicle which was standard and I became very good at gearing down ... never changed brake pads in 10 years but had to do major work on the clutch that would have paid for 3 or 4 sets of pads and maybe a turn on the rotors. I figure regenerative braking will be enough of a savings on brake pads and don't use 'B' to slow down my Prius ...

    Although I may try to use 'B' to bypass the 'hybrid logic' in other situations in the future ... like a backwards donut next winter ... just kidding.

  7. #6

    The answer to your question

    The answer to your question on engine breaking is that the electric motor (MG2) is providing the resistance (I assume maximum) and generating electricity. If the battery cant absorb the energy any excess is being sent to MG1 (the smaller electric motor/generator) which then spins the gas motor above idle. That is the loader noise you are hearing at the bottom of the hill. Just like down shifting in a normal car except that its the electric motor thats spinning it faster.

  8. #7
    Junior Member
    Join Date
    Dec 2007

    The "B", engine Brake mode

    The "B", engine Brake mode for the Prius uses a change in valve timing to turn the engine into an air compressor to increase the compression braking effect.

    This is essentially the same method used in tractor-trailer "Jake Brakes" or Engine Brakes. Use of the "B" mode may cause louder than normal exhaust noise from the muffler.

    The Brake mode causes LOWER MILEAGE because the energy is NOT being returned to the battery thru the generator/motor.

    The Brake mode is normally NEVER used, except for long downhil grades where the battery becomes fully charged, and the car can no longer use the generator to slow the car down. As in normal operation.

    The "B" brake mode is used to save the brake linings from premature wear. Same as in a tractor-trailer.

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