Cadillac STS 2011 Owner's Manual page 150

When the System Does Not Seem to
Work Properly
If the URPA system will not activate due to a temporary
condition a red light will be shown on the rear URPA
display when the shift lever is moved into R (Reverse).
This occurs 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
Your Vehicle on page 6 109.
A trailer was attached to the vehicle, or a bicycle or
an object was hanging out of the trunk during the
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 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.
If the system is still disabled, after driving forward at
least 15 mph (25 km/h), take the vehicle to your dealer.
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