What you are describing is a normal function of that system. Below is an excerpt from the tire pressure monitoring system description in our manual with the answer to your question in bold print.
The tire pressure monitor (TPM) system warns the driver when a significant loss of tire pressure occurs in any of the 4 tires, and allows the driver to display the individual tire pressures, and their locations on the driver information center (DIC).
The system uses the powertrain control module (PCM), instrument panel cluster (IPC), DIC, remote control door lock receiver (RCDLR) a radio frequency (RF) transmitting pressure sensor in each wheel/tire assembly, and the serial data circuit to preform the system functions.
When the vehicle is stationary the sensor's internal accelerometer is inactive, which puts the sensors into a stationary state. In this state the sensors sample tire pressure once every 30 seconds and do not transmit at all if the tire pressures do not change. As vehicle speed increases, centrifugal force activates the sensor's internal accelerometer causing the sensors to go into rolling mode. In this mode the sensors sample pressure once every 30 second and transmit in rolling mode once every 60 seconds. The RCDLR receives and translates the data contained in each sensor's RF transmission into sensor presence, sensor mode, and tire pressure. The RCDLR sends the tire pressure and tire location data to the DIC via the serial data circuit where they are displayed as follows:
• LF TIRE XX PSI
• RF TIRE XX PSI
• RR TIRE XX PSI
• LR TIRE XX PSI
The sensors continuously compare their last transmitted pressure to their current pressure sample and will transmit in re-measure mode if a 8 kPa (1.2 psi) change in tire pressure has been detected in either a stationary, or rolling state. When the TPM system detects a significant loss of tire pressure, the CHECK TIRE PRESSURE message is displayed on the DIC and the low tire pressure indicator is displayed on the IPC. [size=7]Both the message and indicator can be cleared by adjusting the tire pressures to the recommended kPa/psi. The sensor's pressure range is 0-102 psi. The sensors pressure accuracy from--10 to +70 degrees C is +/- 13.7 kPa (2 psi). Refer to Vehicle Certification, Tire Placard, Anti-Theft, and Service Parts ID Label .
The RCDLR has the ability to detect malfunctions within the TPM system. Any malfunction detected will cause the DIC to display the SERVICE TIRE MONITOR message. For more information on other functions of the RCDLR, refer to Keyless Entry System description and Operation.
By federal law the system must make you aware of a 20% lower than required pressure or a specific pressure determined by tire rating. This is a problem when the temperature drops because ten degrees of temperature drop results in one pound lower tire pressure. In the winter months be sure to set your tire pressures to the specification listed on your tire label on the driver door jam when the tires are cold. If you set them after it was in the garage or after a long drive they will be hot and the pressure will be higher causing the light to be on when the temperature drops.
Please ask if you have any further questions.