Principles of Operation

Principles of Operation
The tire pressure monitoring system (TPMS) monitors the air pressure of all 4 road tires. The wheel-mounted tire pressure sensors transmit via radio frequency (RF) signals, to the smart junction box (SJB). TPMS functionality is integral to the SJB. These transmissions are sent approximately every 60 seconds when the vehicle speed exceeds 32 km/h (20 mph). The TPMS function compares each tire pressure sensor transmission against a low-pressure limit. If it has been determined that the tire pressure has fallen below this limit, the SJB communicates this on the vehicle communication bus to the instrument cluster. The instrument cluster then illuminates the TPMS indicator and displays the appropriate messages) in the message center (if equipped).

The system is not affected by wheel and tire rotation.

Ambient Temperature Change and Tire Pressure

CAUTION: Do not inflate tire higher than maximum pressure stamped on tire sidewall.

Tire pressures fluctuate with temperature changes. For this reason, tire pressure must be set to specification when tires are at outdoor ambient temperatures. If the vehicle is allowed to warm up to shop temperatures, and the outside temperature is less than shop temperature, the tire inflation pressure must be adjusted accordingly.

If the tires are inflated to specification at shop temperatures and the vehicle is moved outdoors when the outdoor ambient temperature is tire pressure may drop significantly lower, the tire enough to be detected by the tire pressure monitoring system (TPMS) and activate the TPMS warning lamp.





As the ambient temperature decreases by 6°C (10°F), tire pressure decreases 7 kPa (1 psi). Adjust the tire pressure by 7 kPa (1 psi) for each 6°C (10°F) ambient temperature drop as necessary to keep the tire at the specified vehicle certification label pressure. Refer to the tables to adjust the tire pressure indoors for colder outside temperatures.

TPMS Indicator and Message Center Messages
The TPMS indicator and vehicle message center (if equipped) sometimes displays faults that cannot be resolved by the customer. Treat these messages as TPMS faults that must be serviced.

TPMS Indicator Illuminates Continuously
The TPMS indicator remains on continuously for the following condition:

1. NOTE: If the spare tire is in use, the damaged road tire must be repaired and installed on the vehicle to restore complete TPMS functionality before carrying out any diagnosis.

Low Tire Pressure - The TPMS indicator is illuminated solid and the message center displays "LOW TIRE PRESSURE" (if equipped). This is displayed when any of the tire pressures are low. When this condition exists, the tire pressure must be adjusted to the recommended cold pressure as indicated on the vehicle certification label and the table above. Adjust the air pressure in the tires.

TPMS Indicator Flashes
The TPMS indicator flashes (flashes 20 to 30 seconds) after bulb-check for the following conditions:
1. Tire Pressure Sensor Fault - If equipped, the message center will display "TIRE SENSOR FAULT" when a tire pressure sensor is malfunctioning. GO to Symptom Chart. Symptom Related Diagnostic Procedures
2. No communication with the SJB (TPMS is integral to the SJB) - The TPMS indicator is illuminated when the instrument cluster has received no signals from the SJB for more than 5 seconds. If equipped, the message center displays "TIRE MONITOR FAULT". GO to Symptom Chart. Symptom Related Diagnostic Procedures
3. Tire Pressure Monitor Fault - If equipped, the message center will display "TIRE MONITOR FAULT" when the tire pressure monitoring system is malfunctioning. GO to Symptom Chart. Symptom Related Diagnostic Procedures