brake fluid

A few weeks back, I was letting my 97 540i warm up in drive way (sharp grade) and the brake fluid warning came on. Yesterday, while driving up a steep grade, the light came on again. Where the heck did they hide the master cylinder and where do I add fluid??

Newbie in a Crisis

Beirut Vet

I don't really know where your brake fluid reservoir is, but I'll tell you where it is on my car, and maybe that'll help.
The secret is, on my 1985 535i, anyway, is the power steering and the brakes USE THE SAME FLUID!
I've got a little round canister on the driver's side of the motor, with a hose going to the power steering pump. It's got a 10mm nut on the top of it, holding the lid on tight. I take that off, remove the lid, and inside is a screen. The fluid should be up to the top of the screen, about a 1/2 inch beneath the top of the canister. I fill it up, put the top back on, and that's it.
Flunky
PS-My car has ABS, so I have to use DOT-4 brake fluid.

I also do not know where your reservoir is located, but my 97 528i is located on the driver side under the carbon inlet air filter for the a/c - heater system. This is a large black plastic box located against the fire wall, driver side. This is a total pain in the *** when I have to add fluid. Hope this helps. Doug