Tire Pressure Sensor: Description and Operation

Pressure sensor, tire pressure (754)

Location
The pressure sensor is located in the tire valve.





Main function
The sensor sends information on tire pressure, temperature and rotation direction to the control module, which in turn informs the driver if a tire has air pressure that is too low.

Type
The tire pressure sensor is an integrated sensor with transmitter, battery and valve. It consists of a plastic housing, with an electronic unit, which is cast into an aluminum housing with a valve. Fitted on the valve are a conical seal and a crown nut, used to fit the valve in the edge of the rim. The sensor weighs approximately 38 g.

Connection
Fitted in the sensor is a 3V (500 mAh) lithium battery, which is activated when speed exceeds 20 km/h. The battery is not replaceable.

Function
The pressure sensor measures pressure and temperature in the tire and also its rotation direction. The temperature value is only used in certain markets. Each sensor has a unique code, which is sent with each block of information. The sensors are fitted in special Saab wheel rims. Normally the sensor measures every 10 seconds and transmits once per minute. If the pressure decreases by more than 0.08 bar from the latest measurement then a new transmission takes place after 10 seconds.

When the battery voltage is too low the control module sends a system fault message on the I-bus.