Oldsmobile 2001 Silhouette Owner's Manual page 203

It may also flash red if the ultrasonic sensors are not
kept clean. So be sure to keep your rear bumper free of
mud, dirt, snow, ice and slush or the system may not
work properly. If after cleaning the rear bumper and
driving forward at least 15 mph (25 km/h), the display
continues to flash red, see your dealer.
It will also flash red if your vehicle is moving in
REVERSE (R) at a speed greater than 3 mph (5 km/h).
Other conditions that may affect system performance
include things like the vibrations from a jackhammer or
the compression of air brakes on a very large truck.
As always, drivers should use care when backing up a
vehicle. Always look behind you, being sure to check
for other vehicles, obstructions and blind spots. For
cleaning instructions, see "Cleaning Your Vehicle"
in the Index.
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