Have you go some after-market electronics in the car? Electric motors, electrical accessories, cellular telephones, remote transmitters, power inverters, and portable entertainment equipment can generate RFI affecting the TPM system. Nissan tells you that no metal film or any metal parts should be placed on the windows (affects reception). Mazda has a whole list of no-no's:
1)If an electrical device or equipment near the vehicle shares the same frequency as the tire pressure sensors.
2) If a metal object is placed near the center of the dash, or a large metal object is placed in the right rear seat, it may block RF signals from the tire pressure sensors to the receiver unit.
3) The use of a digital device such as a personal computer or a current converter device that can cause an RFI condition with the receiver unit.
4) If excess snow or ice accumulates, especially around the wheels.
5) When tires with steel reinforcement in the sidewalls are installed.
6) When tire chains are installed.
Ford says the biggest offenders are: Cell Phones, garage door openers, remote starters, and radar detectors - that broadcast on the same frequency as the sensors.
