Tire Pressure Monitoring System (TPMS)-Diagnosis - Principles Of Operation

TIRE PRESSURE MONITORING SYSTEM (TPMS) - DIAGNOSIS

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.

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.

CAUTION:Do not inflate tire higher than maximum pressure stamped on tire sidewall. Premature tire wear or damage to the tire may result.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 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 following tables to adjust the tire pressure indoors for colder outside temperatures.






TPMS Indicator and Message Center Messages

The TPMS indicator sometimes displays faults that cannot be resolved by the customer. Treat these messages as TPMS faults that must be repaired.

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 conditions:

- 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 label and the table above. Adjust the air pressure in the tires.

2.
NOTE:The TPMS sensors do not transmit when the vehicle is stationary. If the vehicle has been stationary for more then 30 minutes, it will be necessary to wake up the sensors so they will transmit the latest tire pressure information to the SJB.If the vehicle has been stationary for more then 30 minutes, perform the following procedure to wake up the TPMS sensors.

- Turn the ignition switch to the ON position.
- Adjust the air pressure in the LF tire.
- Activate the LF TPMS sensor, at least 2 times, using the tire pressure monitor activation tool.
- Repeat Steps 2 and 3 for the remaining tires.
- If the TPMS indicator remains illuminated after adjusting and activating each sensor, GO to Symptom Related Diagnostic Procedures.

TPMS Indicator Flashes

The TPMS indicator flashes 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. 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 received no signals from the SJB for more than 5 seconds. If equipped, the message center displays "TIRE MONITOR FAULT". See 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 or communication with the instrument cluster has been lost. See Symptom Related Diagnostic Procedures.