I recently purchased a 2006 E55 about 3 weeks ago and it has had a Brake warning light come on since I purchased it. The selling dealership said that they had taken the car to the MB dealership and they said the brakes were fine. They said the reason the brake warning was coming on was because the previous owner had replaced the headlights and fog lights with non-OEM lights. They said it would go away if everything was put back to stock. It hadn't been an issue to me until two days ago when I pulled into the driveway the Reduced Braking Power came on and again 3 times yesterday. I was looking for any ideas? Thanks

 

Sounds like a battery issue, to me.

 

Battery for sure.. After weeks of sitting, my car gives me this warning too.. About to pick up a new battery, as I think mine is the original battery