2010 GMC Sierra 1500 Crew Cab Owner's Manual - Page 203

How the System Works URPA comes on automatically when the shift lever is moved into R (Reverse). A single tone sounds to indicate the system is working. URPA operates only at speeds less than 5 mph (8 km/h). An obstacle is indicated by audible beeps. The interval between the beeps becomes shorter as the vehicle gets closer to the obstacle. When the distance is less than 30 cm (12 in) the beeps are continuous. To be detected, objects must be at least 25.4 cm (10 in) off the ground and below tailgate level. Objects must also be within 2.5 m (8 ft) from the rear bumper. This distance may be less during warmer or humid weather. The system can be disabled by pressing the rear park aid disable button located next to the radio. The indicator light will come on and PARK ASSIST OFF displays on the Driver Information Center (DIC) to indicate that URPA is off, see DIC Warnings and Messages on page 4‑66. Notice: If you use URPA while the tailgate is lowered, it may not detect an object behind your vehicle, and you might back into the object and damage your vehicle. Always verify the tailgate is closed when using URPA or turn off URPA when driving with the tailgate lowered. 3-65