Tire Monitoring System: Description and Operation

TIRE PRESSURE MONITORING (TPM) DESCRIPTION
This vehicle has a Tire Pressure Monitoring (TPM) system as standard equipment. It is there to alert the driver when air pressure in any of the vehicle's four tires falls below a predetermined threshold. It alerts the driver with a flashing lamp in the instrument cluster above the fuel gauge (displays "Low Tire") and an audible chime tone.
The low tire pressure warning system utilizes these main components
- Tire Pressure Monitoring Module
- Tire Pressure Sensor/Transmitters (4)
- "Low Tire" Pressure Indicator Lamp
- Body Control Module (indirectly)





The general location of the system components can be seen in the figure. For information on specific components, refer to that individual component.

OPERATION
The Tire Pressure Monitoring (TPM) system operates by monitoring a radio frequency from the tire pressure sensor/transmitters located in each wheel. When the vehicle reaches a speed of approximately 32 km/h (20 mph), centrifugal force created by the wheels rotating closes a roll switch inside each sensor/transmitter, powering up the sensor/transmitter circuitry. The TPM module monitors for transmissions from the sensor/transmitters anytime the ignition is on. The sensor/transmitters will only send out information when vehicle speed is above 32 km/h (20 mph). To facilitate transmitting the radio signal to the module, the valve stem acts as the antenna for the tire pressure sensor/transmitter. When a sensor/transmitter senses that pressure is below one of two calibrated thresholds (low pressure or critical pressure), the TPM system will indirectly operate the "Low Tire" Pressure Indicator Lamp and the chime tone through the Body Control Module (BCM). When tire pressure is low, the "Low Tire" Pressure Indicator Lamp signal circuit will be pulsed to ground by the TPM module for two seconds on and then two seconds off, over and over. The BCM will then illuminate the "Low Tire" Pressure Indicator Lamp at the same rate and sound the audible chime as one single long tone.
When tire pressure is critical, the low tire pressure warning lamp signal circuit will be pulsed to ground by the low tire pressure warning module for one second on and then one second off, over and over. The BCM will then illuminate the "Low Tire" Pressure Indicator Lamp and sound the audible chime at the rate of one second on and one second off. In either case, the TPM module will continue to pulse to ground the "Low Tire" Pressure Indicator Lamp signal circuit until the sensor/transmitter(s) transmits a pressure above the calibrated thresholds (and car is then driven above 32 km/h (20 mph)) or the ignition is turned off. If the conditions has not been corrected when the ignition is turned off, the indicator lamp will remain off when the ignition is turned on again until the vehicle reaches a speed of approximately 32 km/h (20 mph). In the event a Diagnostic Trouble Code (DTC) is set, the "Low Tire" Pressure Indicator Lamp will illuminate continuously until the ignition is turned off.

NOTE: A low tire pressure condition cannot set a Diagnostic Trouble Code (DTC).