Tire Monitoring System: Description and Operation

Tire Pressure Monitor Description and Operation
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), Antilock Brake System (ABS) wheel speed sensor inputs, class 2 serial data circuit, and the Instrument Panel Cluster (IPC) 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 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 EBCM commands the IPC to turn on the LOW TIRE PRESSURE indicator via a class 2 serial data circuit. This indicator does not appear if more than one tire is high or low, or if the system is not properly calibrated. The system does not alert the driver to which tire is high or low. To turn off the LOW TIRE PRESSURE indicator, refer to Tire Pressure Monitor Reset Procedure.