Ford 2016 EXPLORER Owner's Manual page 210

Parking Aids
The system does not offer a particular space
The sensors may be covered (for example, snow, ice or dirt buildup). Covered senors
can affect the system's functionality.
There is not enough room in the parking space for your vehicle to safely park.
There is not enough space for the parking maneuver on the opposite side of the parking
space.
The parking space is farther than 5 ft (1.5 m) or closer than 16 in (0.4 m) away.
The transmission is in reverse ( R). Your vehicle must be moving forward to be able to
detect a parking space.
Your vehicle is going faster than 22 mph (35 km/h) for parallel and 19 mph (30 km/h)
for perpendicular parking.
The system does not position the vehicle where I want in the space
Your vehicle is rolling in the opposite direction of the transmission (rolling forward with
reverse [R] selected).
An irregular curb along the parking space prevents the system from aligning your vehicle
properly.
Vehicles or objects bordering the space may not be positioned correctly.
You pulled your vehicle too far past the parking space. The system performs best when
you drive the same distance past the parking space.
The tires may not be installed or maintained correctly (not inflated correctly, improper
size, or of different sizes).
A repair or alteration has changed detection capabilities.
A parked vehicle has a high attachment (salt sprayer, snowplow or moving truck bed).
The parking space length or position of parked objects changed after your vehicle passed.
The temperature around your vehicle changes quickly (driving from a heated garage
into the cold, or after leaving a car wash).
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Explorer (TUB), enUSA, First Printing