I have a 2004 E320 4Matic wagon with about 150k miles.
It's been sitting in my garage for about 6 weeks since we last drove it.
Coming home from vacation in late July, I noticed a warning on dash saying "brake wear" "visit workshop" in a circle symbol. We were almost home and I didn't think much of it, because I figured it probably needed brake pads.
Yesterday, I decided to take care of it and when I got in car, the SBC kicked on as usual, but it sounds different than it used to. It now sounds more like a buzzing/humming and not it's usual pumping sound. It's also at a higher pitch than I remember. Then the big red warning lights came on and at this point, I can't shift it out of park if I wanted to (I could with bypass in console, but...).
Needless to mention, I can't get past the warning lights. They reset when you turn off car for awhile, but when you get in, the SBC pump runs way more than normal and sounds different.
I checked the brake lights (I heard brake light switch was one cause) and the brake lights come on, but only if key is turned on. Problem?
At this point, I'm not sure what to do. I looked at brake pads without taking wheels off and they don't look bad, but I'm about to investigate pads further to see if sensor has any bearing on my problem.
Ideas? Help!!

 

I put new pads and sensors on front today and after doing so, the SBC pump started sounding the way it should!!
Don't know why, but for whatever reason I guess the SBC couldn't keep up with worn down pads, even though it had plenty of fluid in reservoir and pads were down to about 25% remaining life.
Go figure.
Warning lights went away, pump sounds good and I can drive car again!!