Ford 2011 Explorer Owner's Manual page 316

WARNING: Just prior to the system recognizing a blocked
condition and alerting the driver, the number of missed objects
will increase. To help avoid injuries, NEVER use the BLIS as a
replacement for using the side and rear view mirrors and looking over
your shoulder before changing lanes. BLIS is not a replacement for
careful driving and only an assist.
Once the blockage is removed, the system will require some driving time
and detection of at least two vehicle objects prior to resetting or the
driver can cycle the ignition key. If, however, blockage is still present
after the key cycle, the system will sense again that it is blocked after
driving in traffic.
The following table lists possible causes and actions for this message
being displayed:
The surface of the radar is dirty
or obstructed in some way
The surface of the radar is not
dirty or obstructed
Heavy rainfall or heavy snowfall
is interfering with the radar
signals
Due to the nature of radar technology, it is possible to get a blockage warning
and not be blocked. This is rare and known as a false blockage warning. A
false blocked condition will either self clear or clear after a key cycle.
Trailer tow false alerts
When towing a trailer, the sensors may detect the trailer thus causing a
false alert. It may be desirable to turn the BLIS off if the false alerts
become annoying.
Day and night brightness
The BLIS and/or CTA alert will automatically dim when the headlamp
switch is in PARK, ON, or AUTO ON and night time darkness has been
detected by the sun sensor.
2011 Explorer (exp)
Owners Guide, 1st Printing
USA (fus)
Clean the fascia area in front of the
radar, either side, or remove obstruction.
Drive normally in traffic for a few
minutes to allow the radar to detect that
it is no longer blocked. Note: The
vehicle must be in D (Drive) and a few
vehicles must pass so that the BLIS can
clear a blocked state.
No action required by the driver. The
system will automatically reset to an
unblocked state once the
rainfall/snowfall rate decreases or stops.
Do not use BLIS and/or CTA in heavy
rainfall or heavy snowfall.
Driving
315