2009 GMC Yukon Owner's Manual - Page 123

Power Assist Steps Your vehicle may have power assist steps. The power assist steps automatically extend from beneath the vehicle on the side in which the door has been opened. Once the door is closed, the assist steps automatically move back under the vehicle after a brief delay. The vehicle must not be moving for the assist steps to extend or retract. The switch used to disable the power assist steps is located on the center console below the climate control system. The assist steps cannot be disabled in the extended position. 2-17