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Tire Pressure Monitor Description and Operation

Tire Pressure Monitor Description and Operation

The tire pressure monitor (TPM) system warns the driver when a significant loss, or gain of tire pressure occurs in any of the 4 tires. It allows the driver to display the individual tire pressures and their locations on the driver information center.

The system uses the body control module (BCM), driver information center (DIC), instrument cluster, a radio frequency (RF) transmitting pressure sensor in each wheel/tire assembly, and the serial data circuit to perform the system functions. Each sensor has an internal power supply with an approx. 10 year service life.

When the car is stationary, every sensor's internal accelerometer is inactive, which sets the sensors to sleep mode. In this mode, the sensors read the pressure every 30 seconds and do not transmit signals unless the pressure changes. When the car then starts, the internal accelerometers are activated by centrifugal force and the sensors switch to Drive mode. In this mode, the sensors sample tire pressure once every 30 seconds and transmit in Drive mode once every 60 seconds. The BCM receives and translates the data contained in each sensors RF transmission into sensor presence, sensor mode, and tire pressure. The BCM sends the tire pressure and tire location data to the driver information center via the serial data circuit where they are displayed.

The sensors continuously compare their last pressure sample to their current pressure sample and will transmit in re-measure mode if a 8.3 kPa (1.2 psi) change in tire pressure has been detected in either a stationary state or Drive mode. When the tire pressure monitoring system detects a significant loss, or gain of tire pressure, the tire pressure monitor indicator icon is illuminated on the instrument cluster and if equipped, a check tire pressure type message is displayed on the driver information center. Both the indicator icon and the message can be cleared by adjusting the tire pressures to the recommended kPa/psi and driving the vehicle above 40 km/h (25 mph) for at least 2 minutes.

If power is disconnected from the BCM or if the vehicle battery is disconnected each TPM sensor ID is retained but all of the tire pressure information is lost. Under these circumstances the BCM cannot assume that the tire pressures were maintained over an unknown period of time. If equipped, the driver information center will display all dashes and the scan tool will indicate a default tire pressure value of 1020 kPa (148 psi) for each tire. Driving the vehicle above 40 km/h (25 mph) for at least 2 minutes will activate the sensors causing the driver information center to display the current tire pressures. The special tool EL-46079/J-46079 or EL-50448 activation tool for tire pressure sensors may also be used to activate the sensors.

The BCM can record faults in the tire pressure monitoring system. If a DTC is recorded, the control lamp symbol for tire pressure monitoring in the instrument cluster flashes for 1 minute and then stays on once the ignition has been switched ON and the instrument cluster's bulb check has been completed. Any malfunction detected will cause the driver information center to display a service tire monitor system type message. For more information on other functions of the BCM, refer to Keyless Entry System Description and Operation (without ATH) and Keyless Entry System Description and Operation (with ATH) .