Tire Pressure Monitoring System Operation
The tyre pressure monitor system warns the driver when a significant loss or gain of tyre pressure occurs in any of the 4 tyres. It allows the driver to display the individual tyre pressures and their locations on the driver information centre.
The system uses the body control module (BCM), driver information centre, instrument cluster, remote control door lock receiver, tyre pressure indicator module and a radio frequency transmitting pressure sensor in each tyre assembly. Each sensor has an internal power supply.
When the vehicle is stationary, the sensors 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 pressure does not change. As vehicle speed increases, centrifugal force closes the sensors internal roll switch, which puts the sensor into Wake and then Drive mode. The remote control door lock receiver receives and then sends the tyre pressure and temperature data to the body control module (BCM). The tyre pressure indicator module sends sensor ID and location data to the BCM. The BCM translates the data contained in the tire pressure sensor radio frequency transmissions into sensor presence, sensor mode, and tire pressure. Once vehicle speed is greater than 40 km/h (25 MPH), the remote control door lock receiver waits for the sensors to go into Drive mode.
Each sensor has its own unique identification (ID) code which it transmits as part of each RF message and must be learned into the BCM memory. Once all 4 ID's have been learned and vehicle speed is greater than 40 km/h (25 mph), the BCM continuously compares ID's and pressure data in the received transmissions to the learned ID's and pressures to determine if all 4 sensors are present and if one or more tyres are low. If the BCM detects a low tyre pressure condition, a variation in pressure between 2 tyres on the same axle, or a malfunction in the system, it will send a serial data message to the instrument cluster requesting the appropriate tyre pressure monitor indicator illumination and also to display the appropriate data message on the driver information centre, if equipped.
The sensors continuously compare their last pressure sample to their current pressure sample and will transmit in Learn Mode-Pressure Triggered if a 8.3 kPa (1.2 PSI) change in tyre pressure has been detected in either a Stationary or Drive state. When the tyre pressure system detects a significant loss, or gain of tyre pressure, the tyre pressure monitor indicator icon is continuously illuminated on the instrument cluster and if equipped, a check tyre pressure type message is displayed on the driver information centre.
Both the indicator icon and driver information centre message can be cleared by adjusting the tyre pressures to the recommended kPa/PSI and driving the vehicle above 40 km/h (25 MPH) for at least 9 minutes.
If power is disconnected from the BCM or if the vehicle battery is disconnected each tire pressure 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. Cars equipped with the driver information centre will display dashes and the scan tool will indicate a default tyre pressure value of 1020 kPa (148 PSI) for each tyre. To reactivate the sensors, the vehicle must be driven above 40 km/h (25 MPH) for at least 9 minutes. When the sensors are activated, the driver information centre displays the current tyre pressures.
The BCM has the ability to detect malfunctions within the tire pressure monitor system. In the event a DTC is set, the tyre pressure monitor indicator icon on the instrument cluster will flash for 1 min. and then remain illuminated after the power switch is turned ON and the instrument cluster bulb check has been completed. Any malfunction detected will cause the driver information center to display a service tire monitor system type message.
