Whenever I leave my house and head up a hill 1/2 mile from my house, the brake light warning light goes on. This problem started right after I had my first large tune-up at about 28K miles. I talked to the dealer about it a month later, I had gone on vacation 1 day after the tune up, and he said the brake fluid level might be too high. I looked at that but I doubt it. It looks fine. Any ideas what's going on? The light will go off, but it will come back at odd times.