Tire Pressure Monitoring System Description
Tire Pressure Monitoring System Description
The Tire Pressure Monitoring System (TPMS) is controlled by BCM and works as follows.
TPMS monitors the air pressure in each tire except the spare tire (5). It consists of a low tire pressure warning light (10), tire pressure sensors (1)(2)(3)(4), TPMS receiver (6) and BCM (7).
As the tire revolves (at a vehicle speed of approximately 30 km/h (19 mph) or more), the tire pressure sensor installed to each wheel transmits the tire pressure data through the TPMS receiver to BCM. When the tire pressure is lower than the standard value in the module, BCM makes the low tire pressure warning light in the combination meter light up to warn the driver that the tire pressure has decreased. Also, when anything faulty is detected in TPMS, it makes the low tire pressure warning light lights up after blinks for 75 seconds to warn the driver that there is something faulty in the system.
Operations of the tire pressure sensor, TPMS receiver, BCM and low tire pressure warning light are described below.
Tire pressure sensor
The tire pressure sensor consists of a pressure sensor, rotary sensor, control section, transmitter/receiver, battery and air valve.
Each tire pressure sensor is assigned with an individual ID code. It identifies the sensor condition and outputs it as the function code which is used for BCM to judge whether the tire pressure sensor is operating properly or not. The tire pressure detected by the tire pressure sensor, along with the ID code and function code, is transmitted to the TPMS receiver on the radio wave. As the tire revolves (at a vehicle speed of approximately 30 km/h (19 mph) or more), the pressure sensor transmits the data at 1 minute intervals to TPMS receiver (active mode). However, when 15 minutes have elapsed after the vehicle is stopped (the tire is not revolving (the vehicle speed is less than approximately 10 km/h (6 mph)), the data is sent to the TPMS receiver once an hour so as to prevent consumption of the battery (pause mode). Whether the tire is revolving or not is detected by the rotary sensor.
There are 6 function codes that represent tire pressure sensor state as follows.
- Normal:
The vehicle is at a stop other than Learn, OFF, Re-measure, Low battery and Wake or is running.
- Learn:
The tire pressure sensor is in the mode to register the ID code to BCM.
- Re-measure:
The tire pressure has changed beyond the range of ±8.4 kPa after a specified time, or the air in the tire is overcharged (351 kPa or more).
- Wake:
The tire pressure sensor has changed from the pause mode to the active mode.
- OFF:
The tire pressure sensor is in the data transmission stop mode (new one).
- Low battery:
The battery voltage has reduced.
TPMS receiver
The function of keyless entry receiver is included in TPMS receiver.
The TPMS receiver receives the data from the tire pressure sensor, converts it from the analog signal to the digital signal and transmits it to BCM.
BCM and low tire pressure warning light
BCM receives signals from 4 tire pressure sensors, identifies each data by the ID code of each tire pressure sensor and uses the identified data to compare the air pressure in each tire with the specified value. When the tire pressure is judged as lower than the specified value (190 kPa), BCM makes the low tire pressure warning light in the combination meter lights up and stores the DTC in its memory. Also, when a faulty condition of the system is detected, BCM makes the low tire pressure warning light in the combination meter light up after blinks for 75 seconds and stores the DTC in its memory.
NOTE:
Only up to 4 ID codes of the tire pressure sensor can be registered in BCM. Therefore, when a spare tire or any other sensor equipped wheel with tire is used as a running wheel, ID codes of all tire pressure sensors installed to 4 tires must be re-registered. When the vehicle is driven without re-registration of the ID codes, BCM detects a faulty condition of the system and makes the low tire pressure warning light up after blinks for 75 seconds. For the procedure to register the ID codes of tire pressure sensors in BCM, refer to Registration Procedure for Tire Pressure Sensor ID Code Registration Procedure for Tire Pressure Sensor ID Code.
Vehicle sped signal
BCM uses the vehicle speed signal from ECM to judge if the tire pressure sensor operates properly.