GMC 2011 Sierra Owner's Manual page 371

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 8 km/h (5 mph).
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 comes on and
PARK ASSIST OFF displays on the
Driver Information Center (DIC) to
indicate that URPA is off; see
.
The following messages may be
displayed on the DIC:
message occurs, take the vehicle to
your dealer to repair the system.
This message
occurs if the driver disables the
system.
This
message can occur under the
following conditions:
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 the
Vehicle under
.
If this