No symptoms felt at brake pedal - still high pedal with very good resistance. No pedal softening at traffic lights.

Started car this morning and noticed the Brake Failure stayed illuminated for 5-10 seconds. It's never done that before. Then went off and didn't come on for the 18 mile drive to work. Went out at lunch and drove about 8 miles, everything normal. About 4 miles back toward work I'm driving at a steady speed and the light comes on - I didn't push the pedal and the light came on. Staying on permanently now, at least for the drive home.

Here is what I can say about the car and condition:
* I've owned it since new.
* Has good pads all the way around - I put them about 10k miles ago
* Rear pads recently developed a squeal
* Car still stops on a dime
* New master cylinder 2 years ago because the original was allowing pedal sink
* Original rotors with 200K - the fronts are straight but have significant wear, i.e. probably too thin but no evident problems
* Pedal is solid and everything feels good during depression
* The instrument panel has not been removed in the last 6 months.

So, usual suspect would be the master cylinder with an imbalanced equalizer valve, but I don't feel a problem with the pedal. Could extended piston protrusion in the wheel cylinder, due to thin front rotors, cause a fault light? What do you all think? R2