Your brake sensors are telling you that it's about time to change your pads...not sure if the 400E has rear sensors too, but you have front sensors at the very least.

From experience, you can probably get another 1500-2000 miles out of the current pads unless you are racing. I waited two months at one point before I swapped pads and I saw plenty of meat on the old ones when I did.

I had a pump go out on a 95 SL once...similar issue, no fluid despite full reservoir. Pump was $30, 15 minute job at home to replace. Worked after that.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car