2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 204

When the System Does Not Seem to Work Properly If the URPA system will not activate due to a temporary condition, the messages PARK ASSIST OFF or PARK ASST BLOCKED SEE OWNERS MANUAL will be displayed on the DIC. SERVICE PARK ASSIST: If this message occurs, take the vehicle to your dealer to repair the system. PARK ASSIST OFF: This message occurs if the driver disables the system. PARK ASST BLOCKED SEE OWNERS MANUAL: This message can occur under the following conditions: . . The park assist sensors are covered by frost or ice. Frost or ice can form around and behind the sensors and may not always be seen; this can occur after washing the vehicle in cold weather. The message may not clear until the frost or ice has melted. A trailer was attached to the vehicle, or a bicycle or an object was hanging out of the tailgate during the last drive cycle. Once the attached object is removed and the tailgate is raised, URPA will return to normal operation. A tow bar is attached to the vehicle. The vehicle's bumper is damaged. Take the vehicle to your dealer to repair the system. Other conditions may affect system performance, such as vibrations from a jackhammer or the compression of air brakes on a very large truck. . . . The ultrasonic sensors are not clean. Keep the vehicle's rear bumper free of mud, dirt, snow, ice and slush. For cleaning instructions, see Washing Your Vehicle on page 6‑124. . If the system is still disabled, after driving forward at least 40 km/h (25 mph), take the vehicle to your dealer. 3-66