Check the NHTSA Website. There is currently NO FIX for this issue it plagues all of the similar GM cars with adequate on road time. (Malibu's and G6's primarily. Aura's don't seem to have as much road time or as many on the road).
At least one complaint on the site shows the dealership has been trying, replaced BPP Sensor (Note: this is not a switch anymore!), replaced EBCM, recalibrated BPP(Brake Pedal Position) Sensor, looked at several other options as well. Nothing has worked.
I am currently in the process of working with GM on this issue to get mine fixed under warranty. I am also going to start trying to push for a recall.
I ask that all owners check on their brake lights semi-regularly to see if they are on at times when the brake is not applied. This can be completed in a garage, on the street, in a parking lot, driving at night (note difference in light intensity with brakes applied), or wherever. If you see this fault report it to GM, and the NHTSA! As mentioned this is a serious problem that seems to be plaguing enough people to be seen as a design problem. Reported years 2005 to 2007.