What is a Tyre Pressure Sensor?

Direct tyre sensors transmit real time tyre pressure information to the driver of the vehicle either via either a dashboard display or a warning light.

Tyre pressure sensors are physical pressure and temperature transducers which are attached to the back of the valve stem or are in a form which is banded to the wheel.

What is a Tyre Pressure Sensor?What is a Tyre Pressure Sensor?What is a Tyre Pressure Sensor?

Tyre Pressure Sensor Manufacturers

Tyre pressure sensors are manufactured by international companies such as Schrader, Alligator, Continental, TRW, Pacific, Lear, Beru/HUF and others. There is no common technical standard for the sensors and the OEs and suppliers have generated a multitude of sensor designs. Under normal driving conditions the sensors transmit UHF data such as their unique sensor ID, pressure, temperature and battery status (where applicable) and other diagnostic information. This data is sent to the Engine Control Unit (ECU) or specific receiver on the vehicle. Those vehicles which have graphical displays of the sensor positions can then identify which wheel position has a problem. There can be a significant variation in the data content transmitted by the sensors from different manufacturers and for different make/model/year of vehicles.

Tyre Pressure Sensors & TPMS Tools

Bartec TPMS diagnostic and repair tools have the capabilities to work with all known OE approved sensors. Our work in implementing and testing TPMS in wheel and tyre plants and car plants worldwide supports our market leadership for the long term and ensures that the software is reliable and proven.

A tyre pressure sensor can be of the direct or indirect type according to NHTSA legislation. In practice, nearly all OEs have opted to install direct TPMS in their new builds.

A direct TPMS is a physical pressure and temperature transducer which is usually either valve stem mounted or banded to the wheel and transmits real time tyre pressure information to the driver of the vehicle either via a dashboard display or a tyre pressure warning light on the instrument cluster. The sensors are manufactured by international companies such as Schrader, Alligator, Continental, TRW, Pacific, Lear, Beru/HUF and others. There is no common technical standard (physical, electrical or software protocol) for the sensors and the OEs and suppliers have generated a multitude of sensor designs.

OEs have made great efforts to fit the sensors in the plants to ensure they are at the correct angle when fastening, are correctly torqued using a dynamic torque wrench to ensure that they seal and retain their seal, however, these practices have not yet been adopted in the aftermarket servicing of the TPMS. The OEs also have many electrical tests of the TPMS which have not yet been put into practice in the aftermarket to ensure that systems are properly set up before the vehicle leaves the dealer or tyre shop.

Tyre Pressure Sensor Technology

Sensors transmit data at ultra-high frequency (UHF) such as their unique sensor ID, pressure, temperature and battery status (where applicable) and other diagnostic information. This data is sent to the Engine Control Unit (ECU) or specific receiver on the vehicle. Those vehicles which have graphical displays of the sensor positions can then identify which wheel position has a problem.

This UHF transmission can occur at periodic intervals whilst the vehicle is in motion, immediately and continuously if an under pressure condition occurs or can be forced by a TPMS tool. The TPMS tool is required to force the sensor to transmit if it is being serviced and hence stationary.

A Tyre Pressure Sensor may be replaced for a number of reasons: faulty or damaged sensor, replacement wheels or tyres (winter tyres, and custom wheels) and so on.

The first step should be to use a TPMS tool to audit the vehicle and diagnose any problems such as faulty sensor battery, blocked pressure port, or simply faulty sensor. When removing the tyre from the wheel the technician should be careful where the tyre removal blade is positioned so as not to damage the sensor. The correct replacement part should also be ensured as the sensors from different manufacturers look alike and are easily confused.

In every sensor there is a lithium battery with an expected life of up to 10 years. In order to preserve the battery life some sensors on a stationary vehicle revert to a reduced activity mode. To further preserve the battery life when stored as a replacement part, the TPMS is put into a storage mode (in hibernation). Each manufacturer has a different way to bring the TPMS out of hibernation.

In some cases the sensor has further different modes of operation that also have to be configured:

  • TPMS sensors from Schrader Electronics are supplied as replacement parts in the off mode and are simply commissioned for vehicle use. An activation tool providing a 125 KHz transmission will initialize the TPM for vehicle use
  • TPMS sensors from Beru/Huf are supplied as replacement parts hibernated - Once pressurized over 25 PSI for a period of time they become operational
  • TPMS sensors from Continental are supplied in a number of modes depending on the source of supplier - They can be supplied in TEST MODE and once installed on a vehicle will drive into the correct mode - Alternatively they can be supplied in SHIP MODE in which case they require activation by a 125KHz modulated signal to put them into the correct mode
  • TPMS sensors from TRW are supplied as replacement parts in storage mode - To bring the sensor out of storage mode and to configure it for vehicle use requires a complex modulated 125KHz signal

Sensors can also be activated at low frequency by the TPMS tools which need to take into account the following variations in TPMS technology:

  • Low Frequency (LF) activation using continuous wave
  • Modulated Wave (MW) 125kHz
  • Modulated Wave (MW) 309MHz transmissions

Also some sensors require a forced change in pressure to activate. Most sensors have different modes for test, plant use, transport/storage, drive etc. These are activated using different datagram patterns. The activation of the sensor prompts a UHF response which may have the following variations:

  • Frequency: 315MHz, 433MHz and 434MHz
  • Modulations: ASK and FSK
  • Communications protocols: Manchester, PWM and Bi-phase

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