2005 Ford Expedition Owner's Manual - Page 239

Tires, Wheels and Loading parked. The Low Tire Warning Lamp will turn ON if the tire pressure is 25% below the pressure listed on the Safety Compliance Certification Label (approximately 6 to 9 psi below the manufacturer's recommend tire pressure). If the tire pressure increases 2 psi above the "Light ON" threshold, then the TPMS light will turn OFF. Once the light is illuminated, your tires are under inflated and need to be inflated to the manufacturer's recommended tire pressure. Even if the light turns ON and a short time later turns OFF, your tire pressure still needs to be checked. In short, once the light has turned ON, at least one tire may be under inflated. When your temporary spare tire is installed When one of your road tires needs to be replaced with the temporary spare, the TPMS system will continue to identify an issue to remind you that the damaged road 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 the message center messages (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: 239 2005 Expedition (exd) Owners Guide (post-2002-fmt) USA (fus)