Tire Monitoring System: Description and Operation
TIRE PRESSURE MONITORING SYSTEM (TPMS)
Principles of Operation
NOTE:The smart junction box (SJB) is also known as the generic electronic module (GEM).
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 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.Tire rotation will not affect the TPMS.
Ambient Temperature Change and Tire Pressure
WARNING:The tire pressure monitoring system (TPMS) sensor battery may release hazardous chemicals if exposed to extreme mechanical damage. If these chemicals contact the skin or eyes, flush immediately with water for a minimum of 15 minutes and get prompt medical attention. If any part of the battery is swallowed, contact a physician immediately. When disposing of TPMS sensors, follow the correct procedures for hazardous material disposal. Failure to follow these instructions may result in serious personal injury.
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.
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 (VC) label pressure. Refer to the following tables to adjust the tire pressure indoors for colder outside temperatures.
TPMS Indicator
The TPMS indicator sometimes displays faults that cannot be resolved by the customer. Treat these messages as TPMS faults that must be serviced.
TPMS Indicator Illuminates Continuously
1. The TPMS indicator remains on continuously for the following condition:
- Low Tire Pressure - The TPMS indicator is illuminated solid. 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 (VC) label.
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.
2. If the vehicle has been stationary for more than 30 minutes, carry out the following procedure to wake up the TPMS sensors.
- Turn the ignition switch to the ON position.
- Position the Tire Pressure Monitor Activation Tool against the LF tire sidewall at the tire valve stem.
- Press the test button on the Tire Pressure Monitor Activation Tool to activate the sensor, activate the sensor at least 2 times.
- Repeat Steps 2 and 3 for the remaining tires.
- If the TPMS indicator remains illuminated after adjusting and activating each sensor, see - Symptom Related Diagnostic Procedures.
NOTE:The Tire Pressure Monitor Activation Tool will provide feedback in the form of a flashing green light and a beep sound for each successful response from a tire pressure sensor.
NOTE:The tire pressure sensors will go into a "sleep mode" after 30 minutes of inactivity to conserve battery power. The sensors do not transmit information while in sleep mode. It will be necessary to wake them up so they will transmit the latest tire pressure information.
TPMS Indicator Flashes
The TPMS indicator flashes for 70 seconds, then remains ON solid when the ignition switch is turned to the ON position, for the following conditions:
1. Tire Pressure Sensor Fault - See - 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 not received any signals from the SJB for more than 5 seconds. See - Symptom Related Diagnostic Procedures.
3. Tire Pressure Monitor Fault - See - Symptom Related Diagnostic Procedures.