2008 GMC Sierra 1500 Pickup Owner's Manual - Page 120

How the System Works URPA comes on automatically when the shift lever is moved into REVERSE (R). The rear display will then briefly illuminate to let you know the system is working. URPA operates only at speeds less than 5 mph (8 km/h). If you are above this speed, the red light on the rear display will flash. To be detected, objects must be at least 10 inches (25.4 cm) off the ground and below tailgate level. Objects must also be within 8 feet (2.5 m) from your rear bumper. This distance may be less during warmer or humid weather. A single beep will sound the first time an object is detected between 20 inches (0.5 m) and 8 feet (2.5 m) away. Beeping will occur for three seconds when you are closer than 1 foot (0.3 m) from the object. The following describes what will occur with the URPA display as you get closer to a detected object: Description amber light amber/amber lights amber/amber/red lights amber/amber/red lights flashing and beep for three seconds English 8 ft 40 in 23 in 1 ft Metric 2.5 m 1.0 m 0.6 m 0.3 m The system can be disabled by pressing the rear park aid disable button located next to the radio. The indicator light will come on to indicate that URPA is off. 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. 2-44