Tire Monitoring System: Description and Operation

TPMS System Description

TPMS Control Unit Inputs and Outputs for Connector A (14P)

TPMS Control Unit Inputs and Outputs for Connector B (20P)

System Structure

Whenever the engine is running, the TPMS control unit continuously monitors all four tire pressure sensors and the system function. If it detects low pressure in a tire, it alerts the driver by turning on the low tire pressure indicator and the appropriate tire indicator. If it detects a problem in the system, it turns on the TPMS indicator and the low tire pressure indicator (starts blinking).

Initiators

Mounted on the top of each wheel well, each initiator sends a start/stop signal to the tire pressure sensor in the tire below it.

TPMS control unit

Mounted over the accelerator pedal module, the control unit sends signals to the initiators and receives signals from the tire pressure sensor to verify pressure sensor IDs every time the engine starts. It also receives signals from the transmitters inside the tire pressure sensors, and it continuously monitors and controls the system.

Indicators

All indicators are in the gauge control module: The low tire pressure indicator (LED indicator), the four tire indicators (on the multi-information display) to show which tire is affected, and the TPMS indicator (on the multi-information display) that comes on only if there's a problem with the system. When two or more tire pressures are low, the low tire pressure indicator comes on about 5 seconds before the appropriate tire indicator. Once low pressure is detected, the system scans all four pressure sensors to ensure that it turns on the correct tire indicator.

Tire pressure sensor

Each sensor is an integrated unit made up of the tire valve stem, a pressure sensor, and a transmitter. The unit is attached to the inside of the wheel, around the valve stem. The sensor transmits internal tire pressure to the TPMS control unit when tire pressure is less than 168 kPa (1.7 kgf/cm2, 24 psi). The TPMS control unit then turns on the low tire pressure indicator and the appropriate tire indicator(s). When that tire's pressure is increased to more than 198 kPa (2.0 kgf/cm2, 29 psi), the transmitter sends tire pressure to the TPMS control unit, and then the TPMS control unit turns the indicators off.

Wheels

The TPMS will not work unless TPMS type wheels are installed on the vehicle. The original equipment wheels have a "SJC" mark (A) and a "TPMS" mark (B) on the back of the wheels, and are counterweighted (C) by adding material on the opposite side of the tire pressure sensor (D), to counterbalance the weight of the sensor.

System Communication

- When the vehicle is running, an RF (radio frequency) band wave signal is continuously transmitted from each tire pressure sensor to the TPMS control unit.
- When the ignition switch is turned to ON (II), the initiators send an LF (low frequency) band wave signal to the tire pressure sensors, switching them from sleep mode to normal function mode. When the ignition switch is turned to LOCK (0), the sensors switch from normal function mode back to sleep mode to extend their battery life.
- Each tire pressure sensor has its own tire pressure sensor ID to prevent jamming by similar systems on other vehicles. After memorizing all the sensor IDs, the TPMS control unit receives only those specific signals.
- An tire pressure sensor ID can be memorized manually or automatically. Each initiator is hardwired to the TPMS control unit. Every time the ignition is turned to ON (II), the TPMS control unit asks each initiator for a sensor ID. The initiators then transmit the sensor IDs, and the TPMS control unit receives and memorizes them. The TPMS control unit then knows which sensor ID belongs to each tire location. This recurring sensor ID confirmation prevents any confusion in the system as a result of normal tire rotation.

NOTE: Be careful not to bend the brackets on the TPMS control unit and front/rear initiators: Misalignment of the TPMS control unit and initiators could interfere with sending and receiving signals.