GMC 2008 Yukon Denali Owner's Manual page 144

To be detected, objects must be at least 10 inches
(25.4 cm) off the ground and below liftgate 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
2-46
English Metric
8 ft 2.5 m
40 in 1.0 m
23 in 0.6 m
1 ft 0.3 m
When the System Does Not Seem to
Work Properly
•
The driver disables the system.
•
The parking brake pedal is depressed.
•
The ultrasonic sensors are not clean. Keep your
vehicle's rear bumper free of mud, dirt, snow,
ice and slush. For cleaning instructions, see
Washing Your Vehicle on page 5-102.
•
A trailer was attached to your vehicle, or a bicycle
or an object was hanging out of your liftgate/liftglass
during your last drive cycle, the red light may
illuminate in the rear display. Once the attached
object is removed, URPA will return to normal
operation.
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.