Principles of Operation
Principles of OperationNOTE: For 2007 model year, the tire pressure monitoring system (TPMS) is not available on vehicles having recommended tire pressures that are different for the front and rear tires (for example, front tires: 345 kPa [50 psi] and rear tires: 414 kPa [60 psi]).
The TPMS monitors the air pressure of all 4 road tires. The wheel-mounted tire pressure sensors transmit via radio frequency (RF) signals, to the vehicle security module (VSM). 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 VSM communicates this on the vehicle communication bus to the instrument cluster. The instrument cluster then illuminates the TPMS indicator and displays the appropriate message(s) 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 significantly lower, the tire pressure may drop enough to be detected by the TPMS and activate the TPMS warning lamp indicating a low tire condition.
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 following 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
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.
1. The TPMS indicator remains on continuously for the following condition:
^ 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.
2. NOTE: The TPMS sensors do not transmit when the vehicle is stationary. If the vehicle has been stationary for more than 30 minutes, it will be necessary to wake up the sensors so they will transmit the latest tire pressure information to the VSM.
If the vehicle has been stationary for more than 30 minutes, carry out the following procedure to wake up the TPMS sensors.
1 Turn the ignition switch to the ON position.
2 Adjust the air pressure in the LF tire (as necessary).
3 Activate the LF TPMS sensor, at least 2 times, using the tire pressure monitor activation tool.
4 Repeat Steps 2 and 3 for the remaining tires.
5 If the TPMS indicator remains illuminated after adjusting and activating each sensor, GO to Symptom Chart.
TPMS Indicator Flashes
The TPMS indicator flashes for 70 seconds and then remains ON solid when the ignition key is turned to the ON position 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.
2. No communication with the VSM (TPMS is integral to the VSM) - The TPMS indicator is illuminated when the instrument cluster has received no signals from the VSM for more than 5 seconds. If equipped, the message center displays TIRE MONITOR FAULT. GO to Symptom Chart.
3. Tire Pressure Monitor Fault - If equipped, the message center will display TIRE MONITOR FAULT when the tire pressure monitoring system is malfunctioning or communication with the instrument cluster has been lost. GO to Symptom Chart.