Ford Transit Owner's Handbook Manual page 104

Parking aid
You will hear an intermittent tone at
a distance of up to 180 centimetres
between the obstacle and rear
bumper. Decreasing the distance
accelerates the intermittent tone. A
continuous tone will start at a
distance of less than 40 centimetres.
Note: If a high pitch tone is heard for
three seconds, this indicates a
malfunction. The system will switch
off automatically if it malfunctions.
Have this checked as soon as
possible.
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