Tire Monitoring System: Description and Operation

Tire Pressure Monitoring System (TPMS)

The tire pressure monitoring system (TPMS) includes:
^ the smart junction box (SJB), TPMS functionality 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 SJB compares the information of each tire pressure sensor transmission against a pressure limit. If the SJB determines that the tire pressure has fallen below the low limit, the SJB communicates this to the instrument cluster on the vehicle communication bus.

TPMS Pressure Sensor
The SJB 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 instrument cluster and message center are diagnosed and serviced in their own.

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 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 and displays the appropriate message(s) in the message center (if equipped).

For vehicles with different front and rear tire pressures (such as the F-Super Duty or the E-Series), the tire pressure sensors must be trained following a tire rotation. Failure to train the sensors will result in a false low tire pressure DTC to be set and the TPMS indicator to illuminate.

For vehicles with the same tire pressures for front and rear tires, tire rotation will not affect the system.