Principles Of Operation
Tire Pressure Monitoring System
Principles of Operation
NOTE: The Tire Pressure Monitoring System (TPMS) module is also identified as the Vehicle Security Module (VSM). This module contains only TPMS functionality.
NOTE: This vehicle requires 2 different air pressures - 1 for the front wheels and 1 for the rear wheels. The tire pressure sensors must be trained following every tire rotation. Failure to train the sensors will result in a false low tire event.
The TPMS monitors the air pressure of all 4 road tires via 4 pressure sensors located in the road wheels. Each sensor has a unique identifier number that is sent to the TPMS receiver during system training. The module retains these identifier numbers in memory and associates them with a vehicle position based on the training order. The sensors transmit pressure information to the module via radio frequency signals once every minute when vehicle speed exceeds 32 km/h (20 mph), or once every 6 hours when stationary. The TPMS/VSM is a standalone receiver located behind the glove compartment. The TPMS function compares tire pressure information against a low-pressure limit. If it determines the tire pressure has fallen below this limit, the TPMS/VSM sends a message to the Instrument Cluster (IC) over the Medium Speed Controller Area Network (MS-CAN) bus. Once the IC receives this message, it will illuminate the TPMS indicator.
The tire pressures must be adjusted and the tire pressure sensors must be trained following a tire rotation. Failure to train the sensors will cause the TPMS indicator to illuminate.
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.
NOTICE: Do not inflate tire higher than maximum pressure stamped on the 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 TPMS system 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 (VC) label pressure. Refer to the following tables to adjust the tire pressure indoors for colder outside temperatures.
TPMS/VSM Status PID
The TPMS/VSM monitors the TPMS status. The current status can be viewed by reading the TPMS status PID: TP_STAT using the scan tool. This will help to identify the current system status and may aid in diagnosing the system. The PID has 4 valid states:
1. TP_STAT = SENSOR FAULT.
- If the module has not heard from 1 to 3 TPMS sensors for 20 minutes when the vehicle speed is above 32 km/h (20 mph), the PID will display SENSOR FAULT.
2. TP_STAT = SYSTEM FAULT.
- If the module has not heard from all 4 sensors for 20 minutes and the vehicle speed is above 32 km/h (20 mph), the PID will display SYSTEM FAULT.
3. TP_STAT = LOW.
- If the module has detected that at least 1 sensor is reporting low air pressure, the PID will display LOW.
4. TP_STAT = ACTIVE.
- If the TPMS is functioning normally, the PID will display ACTIVE.
Tire Pressure Monitoring System (TPMS) Indicator
The TPMS indicator may display faults that cannot be resolved by the customer. Treat these messages as TPMS DTCs or symptoms that must be serviced.
Tire Pressure Monitoring System (TPMS) Indicator Remains on Solid from Key ON.
The TPMS indicator will be illuminated solid when the ignition switch is turned to the ON position and any of the tire pressures are low. A DTC will not be present for this condition and the TPMS status PID: STAT will equal LOW. When this condition exists, the tire pressure must be adjusted in all tires to the recommended cold pressure as noted on the Vehicle Certification (VC) label. GO to Symptom Chart. Symptom Related Diagnostic Procedures
TPMS Indicator Flashes
In addition to the TP_STAT PID, the TPMS has an indicator to alert the driver of any potential concerns. The TPMS indicator will flash for 70 seconds and then remain ON solid when the ignition key is turned to the ON position for the following conditions:
Tire Pressure Sensor Fault
One or more (up to 3) tire pressure sensors are malfunctioning or cannot communicate with the TPMS/VSM for more than 20 minutes when the vehicle speed is above 32 km/h (20 mph). The TP_STAT PID will display SENSOR FAULT and DTC B2872 will be present for this condition. GO to Symptom Chart. Symptom Related Diagnostic Procedures
No Communication with the TPMS/VSM
The TPMS/VSM has not received any messages on the Medium Speed Controller Area Network (MS-CAN) bus for more than 5 seconds. The TP_STAT PID will display ACTIVE as the TPMS functionality does not monitor the communication bus. There will be no DTC logged in the TPMS/VSM for this condition, GO to Symptom Chart. Symptom Related Diagnostic Procedures
Communication Issue Between the Instrument Cluster (IC) and the TPMS/VSM
The IC can light the TPMS indicator and set a DTC to signal a communications failure. There will be no TPMS related DTC set under these conditions. If a communications failure is detected by the TPMS/VSM, the DTC U0155 will be present in the module. GO to Symptom Chart. Symptom Related Diagnostic Procedures
Tire Pressure Monitor Fault
The TPMS/VSM has not heard from any of the 4 TPMS sensors for more than 20 minutes and the vehicle speed is above 32 km/h (20 mph). The TP_STAT PID will display SYSTEM FAULT, DTCs B2872 and B287A will be present for this condition. GO to Symptom Chart. Symptom Related Diagnostic Procedures