Tire Monitoring System: Description and Operation

Tire Pressure Monitor Description and Operation (Domestic and Europe Export)
The tire pressure monitor (TPM) system allows the driver to display all 4 tire pressures and their location on the driver information center (DIC) while the vehicle is being driven. The system also alerts the driver when a significant loss or gain of pressure has occurred in any of the 4 tires. The system uses the remote control door lock receiver (RCDLR), instrument panel cluster (IPC), DIC, body control module (BCM), powertrain control module (PCM), a radio frequency (RF) transmitting pressure sensor inside each wheel/tire assembly, and the serial data circuit to perform the system functions. When the vehicle is stationary for more then 15 minutes the sensors go into stationary mode. In this mode the sensors transmit once every 60 minutes, to minimize sensor battery consumption. As vehicle speed increases to 32 km/h (20 mph) centrifugal force closes the sensors internal roll switch causing the sensor to go into drive mode. In this mode the sensors transmit once every 60 seconds to the RCDLR. The RCDLR translates the data within the sensors RF transmission into sensor presents, sensor mode and tire pressure. The RCDLR sends this data to the DIC via the serial data circuit where the tire pressures and their location are displayed as follows:
^ FRONT L XX R XX kPa/psi
^ REAR L XX R XX kPa/psi

When the TPM system detects a low tire pressure condition, approximately 96 - 165 kPa (10 - 24 psi), or a flat tire pressure condition, approximately 0 - 68 kPa (0 - 9 psi), the IPC displays the low tire pressure indicator, which appears as a cross section of a tire with an exclamation mark inside, and the DIC displays the following warning messages:
^ LOW TIRE PRESS XX
^ XX TIRE FLAT/MAXIMUM SPEED 55 MPH REDUCED HANDLING

When the TPM system detects a high tire pressure condition, approximately 248 kPa (39 psi), or greater, the DIC displays the HIGH TIRE PRESS XX warning message.

These messages can be cleared by adjusting the tire pressures to the recommended kPa/psi. Refer to Tire Inflation Pressure Specifications in Maintenance and Lubrication or to Tire Placard in General Information. The sensors pressure accuracy from -10 to 70°C (14 to 158°F) is plus or minus 14 kPa (2 psi). The TPM system can also compensate for high and low altitudes using the PCMs barometric pressure sensor via the serial data circuit. The RCDLR has the ability to detect malfunctions with in the TPM system. Any malfunctions detected will cause the DIC to display the SERVICE TIRE MONITOR warning message on the DIC. For further information on other functions of the RCDLR, refer to Keyless Entry System Description and Operation in Keyless Entry. For further information on which serial data circuits are used by the TPM system, refer to Data Link References in Computer/Integrating Systems.

Tire Pressure Monitor Description and Operation (Japan Export Only)
The tire pressure monitor (TPM) system alerts the driver when a large change in the pressure of one tire exists, while the vehicle is being driven. The TPM system uses the electronic brake control module (EBCM), ABS wheel speed sensor inputs, the GMLAN serial data circuit, and the driver information center (DIC) to perform the system functions. The EBCM contains software to calculate relative tire pressure differences. The software requires approximately 30 minutes of straight line driving in each of the three different speed ranges to complete the calibration process to have full capability for detecting a tire pressure condition. The speed ranges are as follows:
^ 24 - 64 km/h (15 - 40 mph)
^ 64 - 113 km/h (40 - 70 mph)
^ 113 - 145 km/h (70 - 90 mph)

Each speed range has 2 modes of tire pressure detection:
^ Monitor Mode 1
^ Monitor Mode 2

The EBCM learns the tire pressure calibration for each speed range independently. In Monitor Mode 1, the EBCM has only partially learned the tire pressure calibration for the speed range and has limited detection capability for a tire pressure condition. In Monitor Mode 2, the EBCM has fully learned the tire pressure calibration for the speed range and has full detection capability for a tire pressure condition. Once the TPM system has fully learned the tire pressure calibration the EBCM monitors the ABS wheel speed sensor inputs, which will all be the same as the learned calibration if the tire pressures stay the same, If the tire pressure increases or decreases in one tire so to will that tires circumference and radius, which causes that wheel speed sensor input to change. The EBCM recognizes this change in wheel speed as a tire pressure condition. If the pressure in one tire becomes at least 69 kPa (10 psi) higher or lower than the other three the DIC will display the CHECK TIRE PRESSURE warning message via the GMLAN serial data circuit. This message does not appear if more than one tire is high or low, or if the system is not at least partially calibrated. The system does not alert the driver to which tire is high or low. If the tire pressures are at the specified kPa/psi the TIRE PRESSURE NORMAL message is displayed when selected on the DIC. To clear the CHECK TIRE PRESSURE warning message refer to Tire Pressure Monitor Reset Procedure.