It lost fluid if you added. There is a lot of plastic that catches fluid.

I think I see what you are saying; pedal went down so you thought low fluid and added. Was the fluid low before you added?

If it got low air could have gotten in and cause pedal to the ground symptom else a possiblity is problem with the master cylinder.

What scanning solution do you have? You need something like foxwell or computer based to bleed abs.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)