I just looked up my problem online and got several different possibilities:
- brake fluid level low
- brake pads worn
- ice buildup preventing the brake cable from releasing all the way and tripping the switch
- some fault at the sensor
- some fault at the gauge
I'm inclined to dismiss items 1, 2, and 5 as being too coincidental. (Why should they happen now, during the coldest weather we've had in, I think, a few years?) Item 3 sounds like it could be fixed by parking for a few hours in a warm environment. Item 4 sounds like the sort of thing that can happen when half a dozen different ice melt formulations are being splashed onto the underside of your car each day.
I'd like to meet some friends for dinner tomorrow but that may not be possible, given my current car situation.
Tuesday it's back to work.
UPDATE, 1/19/09: They can't see me until Thursday. So I'll drive my car across town like that anyway, to shovel my sidewalks. I wish I lived closer to the Steamtown Mall - they have a heated parkade.
UPDATE, 1/21/09: Well, I fixed it, but I'm not sure how. With access to my car in the daylight for the first time since this problem arose, I dug out the owner's manual and found that it actually covers this sort of problem. The "first aid" advice is to check and top off the brake fluid. I tried to check the level, scraping off as much grime as I could from the outside, and it looked low.
This afternoon I drove the nine miles to the nearest auto parts store to pick up some brake fluid, the brake light on the whole way. When I began to add it, still parked in front of the store, it suddenly seemed like the level was high - so high that it seemed to be right up to the filter screen where you add it, well above the "MAX" mark. (Which would explain why I didn't see a fluid level line.) I added only a few drops before I stopped - both the manual and the bottle give dire warnings about spilling the brake fluid on anything. I decided to drive home and try to figure out next steps. I went into the car, turned on the ignition, and all the usual lights lit up on the dashboard, including the BRAKE light. I then reached for the gear shift, and discovered that I had instinctively set the parking brake when I got to the store, even though I am trying to make a point not to. I released the brake - and the light went out. Problem solved.
But what did it? The past few days have seen moments where the car has warmed up enough to melt ice. Was the trip to the auto parts store enough to dislodge the last few crystals of ice that were blocking the sensor? Or did the thimbleful of brake fluid that I added do the trick? I don't know. If I hadn't set the parking brake, if I had started up the car momentarily before I added the brake fluid, I might have found out. But for now I have no idea.
I'll check my car tomorrow morning before I cancel that appointment at the garage.