2009 GMC Envoy Owner's Manual - Page 250

Using ABS Do not pump the brakes. Just hold the brake pedal down firmly and let antilock work. The brakes might vibrate or some noise might be heard, but this is normal. StabiliTrak® System The vehicle has the StabiliTrak system which combines antilock brake, traction and stability control systems and helps the driver maintain directional control of the vehicle in most driving conditions. Traction control activates when the controller senses wheel spin. StabiliTrak will selectively apply the brakes and reduce engine torque to help regain traction. Stability control activates when the controller senses a discrepancy between the intended path and the direction the vehicle is travelling. StabiliTrak selectively applies braking pressure at any one of the vehicle's brakes to help guide the vehicle in the intended direction. When you first start the vehicle and begin to drive away, the system performs several diagnostic checks to insure there are no problems. The system may be heard or felt while it is working. This is normal and does not mean there is a problem with the vehicle. If driving conditions delay system initialization, the STABILITRAK NOT READY message may be displayed on the Driver Information Center (DIC). If this is the case, the vehicle does not need servicing. For more information on the stability messages, see DIC Warnings and Messages on page 3-51. Braking in Emergencies ABS allows the driver to steer and brake at the same time. In many emergencies, steering can help more than even the very best braking. Brake Assist This vehicle has a Brake Assist feature designed to assist the driver in stopping or decreasing vehicle speed in emergency driving conditions. This feature uses the stability system hydraulic brake control module to supplement the power brake system under conditions where the driver has quickly and forcefully applied the brake pedal in an attempt to quickly stop or slow down the vehicle. The stability system hydraulic brake control module increases brake pressure at each corner of the vehicle until the ABS activates. Minor brake pedal pulsations or pedal movement during this time is normal and the driver should continue to apply the brake pedal as the driving situation dictates The Brake Assist feature will automatically disengage when the brake pedal is released or brake pedal pressure is quickly decreased. 4-6