Ford Mondeo Owner's Manual page 79

If the system senses a fault on either
sensor, the system warning symbol will
illuminate and remain on. The information
display will confirm the fault and indicate
whether the left or right side is affected.
Blocked sensor
WARNING
Prior to the system recognizing a
blocked condition and issuing a
warning, the number of missed
objects will increase.
CAUTION
The sensors may not detect vehicles
in heavy rain or other conditions that
cause disruptive reflections.
Note: Keep the rear bumper area
surrounding the sensors free from dirt, ice
and snow.
If a sensor becomes blocked the system
performance may degrade. A blocked
sensor message may be displayed.
The system will automatically return to
normal operation once two other vehicles
have been detected on both sides.
Trailer towing false alerts
CAUTION
Vehicles fitted with a trailer tow
module not approved by us may not
correctly be detected. Switch the
system off to avoid false alerts. See
Information Displays (page 84).
Windows and Mirrors
77
If the vehicle is fitted with a trailer tow
module approved by us, the system will
detect a connected trailer and deactivate.
A confirmation message will be shown in
the information display. See Information
Messages (page 97). The BLIS warning
indicator will illuminate. See Warning
Lamps and Indicators (page 80).