Volkswagen - Golf :: Brake Indicator Light Lit Up And Beeping Intermittently

I drive a 2000 VW Golf with 148K miles on it. One Saturday this summer my brake indicator light started lighting and beeping intermittently as I was driving. My brakes were operating fine so I did not read my owners manual until I reached my home. It indicated that I needed to have a qualified mechanic check it immediately but as it was almost 4 o'clock in the afternoon I couldn't find a mechanic in any gas station or garage. As I had a 200 mile drive to do the next day, I purchased brake fluid and carefully followed all of the directions for checking and filling my brake fluid.

However, when I took the cap off of the reservoir, the reservoir really looked fine and I was only able to add about a teaspoon max of brake fluid. However, when I tried driving the car, it seemed that the problem was solved as the brake indicator light did not come on again. Approximately 3 months later now the brake indicator light is intermittently going on again: about every other day. It goes on and then shortly after it goes off and then it doesn't come on again for a day or two.

Inasmuch as I added such a small amount of brake fluid last time I'm really not sure that the problem is actually with the fluid. I wondered if perhaps it was more of a vacuum problem or that by opening the reservoir some air escaped or something of that nature. I also wonder if possibly there's a component that's giving a false reading. At any rate, I'm a little white-haired old lady and there's a limit to what I can do on my car myself and I'm also a target whenever I go into a shop to get the most expensive diagnosis and fix. I'd like to go in to a shop with good information so that it doesn't become an expensive fishing expedition. What could be causing this?