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      09-12-2019, 09:02 PM   #1
alleyooptroop
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40e subtle buzzing sound every time I brake

I recently purchased a CPO ‘16 40e. Really love it so far! I’m just noticing a faint buzzing sound when in all electric mode when I come to a complete stop. It sounds like a cell phone in silent mode. It’s consistent happening every time. Is this just a quirk of the hybrid system? Only thing I found online was from a 530e owner who reported the same thing. Someone in that thread replied saying it was a product of the regenerative braking. Thanks in advance for any replies.
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      09-13-2019, 09:12 AM   #2
pennsiveguy
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Quote:
Originally Posted by alleyooptroop View Post
I recently purchased a CPO ‘16 40e. Really love it so far! I’m just noticing a faint buzzing sound when in all electric mode when I come to a complete stop. It sounds like a cell phone in silent mode. It’s consistent happening every time. Is this just a quirk of the hybrid system? Only thing I found online was from a 530e owner who reported the same thing. Someone in that thread replied saying it was a product of the regenerative braking. Thanks in advance for any replies.
My guess is that you're hearing the electric brake assist motor. Without engine vacuum, something has to replace the "power" in your power brakes, so that they have the same "feel" and pedal effort as when you're operating under engine power. Most of these systems use an electric motor for that. When you're stopped without the engine running is when you're most likely to notice the noise. Many diesel trucks with hydraulic brakes use electric power for 100% of their power brake boost, since a diesel never produces vacuum.

Just my hunch. Somebody on here knows and can give you the real answer if I'm wrong.
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      09-13-2019, 02:53 PM   #3
alleyooptroop
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Originally Posted by pennsiveguy View Post
My guess is that you're hearing the electric brake assist motor. Without engine vacuum, something has to replace the "power" in your power brakes, so that they have the same "feel" and pedal effort as when you're operating under engine power. Most of these systems use an electric motor for that. When you're stopped without the engine running is when you're most likely to notice the noise. Many diesel trucks with hydraulic brakes use electric power for 100% of their power brake boost, since a diesel never produces vacuum.

Just my hunch. Somebody on here knows and can give you the real answer if I'm wrong.
appreciate you chiming in! would love to hear other opinions.
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