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      03-25-2020, 02:21 PM   #1
mvolps22
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Brake Vacuum Pressure sensor or vacuum leak?

My car will periodically not start and I believe it is a brake vacuum issue. The times it won't start the brake pedal is very stiff and it's almost like the car (6MT) doesn't know I have the brake pedal depressed. Nothing happens, no check engine lights, no codes, no limp mode, nothing...car goes in to on mode but starter won't do anything. Should I replace the vacuum line and sensor (34302283605) and booster gasket (34336765316)? could it just be a bad gasket since I'm not getting any codes? It would be nice to save $200 if i only need to replace the gasket. Any thoughts are appreciated!

Parts diagram
https://www.realoem.com/bmw/enUS/sho...diagId=34_1627
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      03-25-2020, 07:15 PM   #2
Redd
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If you press the start button, does it crank and doesn't start? Or does it not crank at all?
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      03-25-2020, 08:32 PM   #3
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Quote:
Originally Posted by Redd View Post
If you press the start button, does it crank and doesn't start? Or does it not crank at all?
Doesn't crank at all, dash lights up, everything else is normal.
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      03-25-2020, 08:44 PM   #4
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Very common, if you don't drive your car for a few weeks.

Just press the stiff brake pedal a little harder (Incredible Hulk - Beast Mode) and it will start up fine.

If your brake vacuum/master cylinder leaks slowly over several weeks, the brake pedal gets really stiff. It is as if the DME computer doesn't think you have your foot on the brake before starting. Too weird.

If the car cranks slowly, your battery might be depleted from the car not being driven.
AGM Battery only lasts 6-8 years.

Same thing happened to me on a newish 2015 F30 335i, as well as, my 2009 E90 M3 with 190k miles. Don't waste money on a new brake master cylinder, or vacuum pump.


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      03-25-2020, 09:24 PM   #5
mvolps22
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Quote:
Originally Posted by nyc_dude View Post
Very common, if you don't drive your car for a few weeks.

Just press the stiff brake pedal a little harder (Incredible Hulk - Beast Mode) and it will start up fine.

If your brake vacuum/master cylinder leaks slowly over several weeks, the brake pedal gets really stiff. It is as if the DME computer doesn't think you have your foot on the brake before starting. Too weird.

If the car cranks slowly, your battery might be depleted from the car not being driven.
AGM Battery only lasts 6-8 years.

Same thing happened to me on a newish 2015 F30 335i, as well as, my 2009 E90 M3 with 190k miles. Don't waste money on a new brake master cylinder, or vacuum pump.


Cheers

It has happened at the gas station, after work, etc, doesn't seem to be correlated to how long it sits. Could be 5 minutes while getting gas, or 8 -12 hours while parked at home or the office. I usually just have to wait 15 minutes to an hour and then it will start like normal. I really don't think I can push the brake down to the point the car would start, I've tried to the point I thought the seat back was going to break.

Last edited by mvolps22; 03-25-2020 at 09:36 PM..
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      03-25-2020, 09:35 PM   #6
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Take it to a good BMW Indie Shop to see if they can check the brake vacuum and battery voltage. They can read any hidden codes. Try pumping the brakes and then start.

Also see if the fuel tank breather valve needs replacing...should see an emissions CEL.
Car will have issues after filing up the fuel tank at the gas station, if the fuel tank breather valve is bad.

Lastly, if the is no power and your courtesy lights and dash don't light up, then it could be the positive battery cable recall.

Waiting an hours until it starts is crazy.


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      03-25-2020, 11:17 PM   #7
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Yeah sounds electrical more than brake vacuum related. Check ground cable also.
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