Roll Switch
WARNING: This page is about a different car, the 2006 Dodge Viper. However, it is still accessible from the selected car via links, so may be relevant.
There is an integral roll switch within the Tire Pressure/Sensor Transmitter that must be closed before the transmitter is enabled. This roll switch is open when the vehicle is stopped or below 33 km/h (20 mph.) When the vehicle is moving above 33 km/h (20 mph) centrifugal force will close the roll switch.
NOTE:
The transmitter will continue to transmit for 15 minutes and once an hour after the roll switch has opened. If a transmitter is tested with Miller tool 9001, and it is determined that a RF signal is present, the vehicle must driven to verify roll switch closure.