Tire Monitoring System: Description and Operation
TIRE PRESSURE MONITORING SYSTEM (TPMS)Wheels And Tires
Warning:
^ Do not mix different types of tires on the same vehicle such as radial, bias or bias-belted tires except in emergencies (temporary spare usage), because vehicle handling may be seriously affected and may result in loss of control. Failure to follow these instructions may result in personal injury.
Factory-installed tires and wheels are designed to operate satisfactorily with loads up to and including full-rated load capacity when inflated to recommended inflation pressures.
Correct tire pressure and driving techniques have an important influence on tire life. Heavy cornering, excessively rapid acceleration and unnecessary sharp braking increase tire wear.
To equalize tire wear, the tires should be rotated at recommended intervals.
Safety Precautions
Warning:
^ Never run the engine with one wheel off the ground, for example, when changing a tire. The wheel(s) resting on the ground could cause the vehicle to move. Failure to follow these instructions may result in personal injury.
Warning:
^ The tire and wheel must always be correctly matched. It is very important to determine the size of each component before any assembly operations commence. Failure to adhere to these instructions can result in an explosive separation and cause serious bodily injury or death.
Warning:
^ Aftermarket aerosol tire sealants are extremely flammable. Always question the customer to make sure these products have not been used. Failure to follow these instructions may result in personal injury.
Warning:
^ Aftermarket wheel assemblies may not be compatible with the vehicle. Use of incompatible wheel assemblies can result in equipment failure and possible injury. Use only approved wheel assemblies. Failure to follow these instructions may result in personal injury.
Warning:
^ Use only wheels and wheel nuts that have been designed for current model vehicles. Aftermarket wheels or wheel nuts may not fit or function correctly. Failure to follow these instructions may result in personal injury.
Warning:
^ Always wear safety goggles or a face shield when performing any work with the tire and wheel assemblies. Failure to follow these instructions may result in personal injury.
Caution:
^ Reduce the air pressure as much as possible by pushing the valve core plunger in prior to removing the valve core. Avoid working in a position in which the face or body directly over a tire in which there is pressure.
Caution:
^ Do not clean aluminum wheels with steel wool, abrasive-type cleaners or strong detergents. Use Wheel and Tire Cleaner ZC-37-A-B or equivalent.
When carrying out any inspection or repair procedures on wheels and tires, follow the preceding safety precautions.
Tire Pressure Monitoring System (TPMS)
The tire pressure monitoring system includes:
^ the smart junction box (SJB), TPMS is integrated within the SJB.
^ four tire pressure sensors.
^ four tire pressure sensor cradles.
^ four tire pressure sensor straps.
^ an instrument cluster indicator.
^ a message center (if equipped).
TPMS System Module
The SJB contains the TPMS functionality. The 2 systems have separate diagnosis and testing but they are serviced as one module.
The SJB compares the information of each tire pressure sensor transmission against a pressure limit. the SJB determines that the tire pressure has fallen below the low limit (the pressure listed on the vehicle certification label minus 25%), the SJB communicates this to the instrument duster on the vehicle communication bus.
TPMS Pressure Sensor
The TPMS monitors the air pressure in the 4 road tires with tire pressure sensors. The sensors transmit radio frequency (RF) signals to the SJB approximately every 60 seconds when the vehicle speed exceeds 32 km/h (20 mph).
The tire pressure sensors are battery operated and are mounted to metal brackets (called cradles) on the wheels inside the tires. The sensors are mounted 180 degrees from the valve stem.
The tire pressure sensor can be serviced separately from the cradle and the strap.
TPMS Pressure Sensor Cradle
The tire pressure sensor cradles are mounted to the wheels with metal straps and have an adhesive strip to aid in their retention to the wheel. To service the sensor cradle, the strap must also be removed.
TPMS Pressure Sensor Strap
The sensor strap is what keeps the sensor and the cradle retained to the wheel. A factory-installed strap is joined together with a one-time use buckle and a dealer installed strap is joined together with a worm gear (similar to a radiator hose clamp). Both straps should be discarded after removal and should not be re-used.
The strap can be serviced separately from the sensor and the cradle. The sensor is available separately from the cradle and the strap. The cradle and strap are available as a strap kit. There are several different strap kits available based on wheel diameter, all strap kits share the same base part number.
Instrument Cluster and Message Center
The instrument cluster illuminates the TPMS indicator when it receives a message from the SJB to do so and displays the appropriate message(s) in the message center (if equipped). The indicator must illuminate when the tire pressure has fallen below 25% of what is listed on the vehicle certification label, but it may illuminate sooner.
The instrument cluster and message center are diagnosed and replaced in their own respective workshop manual sections.
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 duster. 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 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.
Table 1. Use Table To Adjust Tire Pressure Inside Garage For Colder Outside Temperature:
Table 2. Use Table To Adjust Tire Pressure Inside Garage For Colder Outside Temperature (Metric):
