Been searching every forum for answers, no one has had issue like this, or the couple I did find did not post the solution, so with only the brake booster left to change, will get around to it and let everyone know in case you experience this crazy issue. The only code I ever got was front right wheel sensor, replaced, no difference, then had pressure sensor code, replaced, no change, but no more codes. Was going to buy latest BMW diagnostics to see if any hidden codes show up that my scanner does not show. Anyone know if all BMW interface cables are the same, or any suggestions, had only downloaded software to date. Parked car for now.


Funny thing, brake pedal is harder now, squeaks and airy hisses now when I press pedal hard to stop, so this leads me to believe brake booster was going bad little by little, pinched of vacuum hose which should have isolated problem, as in, the pedal was hard to push, but still locked up the same, so I did not think it could be brake booster initially, but that was before squeak in brake pedal and hissing sound, so hope that is it.

See this video:

https://youtu.be/G95-S9i40R8

Car with two bad check valves in the master cylinder caused all four brakes to lock up.


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Did you remove the bleeder screws and inspect them for corrosion? Put teflon tape on the threads?

https://www.youtube.com/watch?v=_LLJXUbQkdA