Last Tuesday the brake failure light came on in my 1990 Volvo 240 sedan. The brakes felt fine, the brake fluid was full. Took it to my mechanic on Thursday who could find no leaks. He flushed the brake system and the light went out. Four hours later the brake failure light came back on. The brakes still feel fine, fluid is full, normal pedal travel, etc.
The master cylinder was replaced last June or July because I was noticing some brake fade. Brake pads (and I think the front rotors too) were replaced two or three years ago.
My mechanic opined that either the problem is with the master cylinder or possibly the brake balance sensor (my paraphrase, I can't remember exactly what he called it) is bad and there's nothing actually wrong with the brakes.
Any opinions would be welcome. Thanks!