Tire Pressure Sensor: Description and Operation
SENSOR-TPMDESCRIPTION
Fig. 17 Sensor Mounting - Exploded View:
On vehicles equipped with Tire Pressure Monitoring (TPM), one tire pressure sensor (6) is mounted to each wheel (5) in place of the traditional tire valve stem (Fig. 17). Each sensor has an internal battery that lasts up to 10 years. The battery is not serviceable. At the time of battery failure, the sensor must be replaced.
Fig. 18 Tire Pressure Sensor:
The TPM system operates on a 315 MHz radio frequency. Corporate 315 MHz sensors can be easily identified by a white outline oval (black center) insignia (3) on the sensor body (Fig. 18).
The TPM sensors are designed for original style factory wheels. Do not attempt to install a tire pressure sensor in an aftermarket wheel. If aftermarket wheels are installed and do not contain tire pressure sensors, the system will not function properly and the driver will be continuously notified of a system malfunction.
The serviceable components of the tire pressure sensor are (Fig. 17):
^ Sensor-To-Wheel Seal and Metal Washer
^ Valve Stem Cap
^ Valve Stem Core
^ Valve Stem Nut (with pressed-in washer)
The valve stem caps and cores used are specifically designed for the tire pressure monitoring sensors. Although similar to standard valve stem caps and cores, they are different. The valve stem cap has a special seal inside to keep moisture and corrosion out. The valve stem core has a special nickel coating to protect from corrosion.
OPERATION
The battery operated tire pressure sensors lay dormant (Park Mode), then wake and start transmitting (Drive Mode) when the vehicle first reaches speeds over 15 mph (24 km/h). Once the wheels stop rotating for a period of approximately 20 minutes, the sensors shut down until again awaken. Although not transmitting as when in Drive Mode, while in Park Mode, the sensors still transmit approximately once every 13 hours to let the receiver know air pressure status at that time. Sensors will also transmit when a pressure change of one psi (seven kPa) or more is detected during that period.
Using an RF signal, each sensor transmits tire pressure data approximately once every minute. Each sensor's (transmitter) broadcast is uniquely coded so that the Wireless Control Module (WCM), commonly referred to as the Sentry Key Remote Entry Module (SKREEM), can monitor the state of each of the sensors in the four rotating road wheels. The WCM automatically learns and stores the sensor's ID while driving after a sensor has been replaced. This can take up to 10 minutes while driving at speeds above 15 mph (24 km/h). There is no formal retraining procedure necessary