Welcome to those with similar problem.
Don,t know why GM has not issue a recall for this situation that has seen there are many and is a Safety Problem; if you have a real brake problem you will not notice any warning because you warning light is already "on"
I tried some recomendations like new alternator, air bleed lines and clean electrical grounds. Still problem persits.
Read a mail that one user went the expensive way and replaced the EHCU and warning lights came on again.
Hope some body have the answer and writes.