Do you have traction control or does this only occur when you press the brake pedal? False activation when you press the brake pedal is often due to a loss of the signal from one of the wheel speed sensors. GM has a lot of trouble with wheel bearings causing that on front-wheel-drive vehicles in as little as 15,000 miles. Rust buildup between the sensors and where they bolt onto the bearing assembly is another common problem. Also look for rust and metal particles on the ends of the sensors. The best way to determine which sensor is causing the problem is to watch the speed readings on a scanner during a test drive.