Ford Freestar 2006 Owner's Manual page 196

Tires, Wheels and Loading
wheel/tire needs to be repaired and put back on your vehicle. During this
time, the low tire warning light can periodically return or stay on,
depending on the state of the damaged road wheel/tire. This will include
messages from the message center (if equipped).
To restore the full functionality of the Tire Pressure Monitoring System,
have the damaged road wheel/tire repaired and remounted on your
vehicle. For additional information, refer to Changing tires with TPMS
in this section.
When you believe your system is not operating properly
The main function of the Tire Pressure Monitoring System is to warn you
when your tires need air. It can also warn you in the event the system is
no longer capable of functioning as intended. Please refer to the
following chart for information concerning your Tire Pressure Monitoring
System:
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