2008 Pontiac Grand Prix NO Brake lights

Brakes problem
2008 Pontiac Grand Prix V8 Front Wheel Drive Automatic 15k miles

Hello everyone, I am purchasing a 2008 GXP it only has 15000 miles on it.
I am trading the wifes 06 fusion in on it. I have had two other grand prixs and loved them one was a 02GTP and the last was a 2004GTP.
I have not picked up the car yet cause the dealership that is getting my car ready found that it was flashing a sign in the Driver Information Center that say traction control and abs are not working they say that they needed to replace the BCM and that did not fix it now they say that it needed a PCBM they replaced it and still no brake lights. The flashers work and they can make the Brake lights come on with the scan machine. It has been in the shop for 2wks now they think maybe they will try another BCM witch will be in Monday. I am getting a little flustered I have made a deal to trade and I know it is still under warranty but I want to drive my car and can not. Has anyone ever herd or experienced a problaem like this. They say that the reason the the lights are flashing on the DIC is because the car know that the brake lights are inop and this is way they are flashing