What is TPMS?
TPMS stands for Tyre Pressure Monitoring System, a safety feature that continually monitors a vehicles' tyres and alerts the driver to changes in tyre pressure. The changes in tyre pressure can be detected by either Direct or Indirect means but both methods will, as a minimum, illuminate a warning light on the vehicle dashboard display and sound an audible alert when 25% deflation has occurred.
Early TPMS were first introduced as an option on high-end luxury vehicles as early as the 1980s, although it wasn't until the year 2000 that it was first fitted as a standard feature.
Tyre Pressure Monitoring and the Law in Europe
- From November 2012 all new type vehicles in the M1 category (vehicles under 3.5 Tonnes with less than 8 seats) will be required by law to have Tyre Pressure Monitoring System installed. This applies to the road wheels not the spare.
- By November 2014 all new passenger vehicles will have to have TPMS installed by the manufacturer.
- The law is not currently retrospective, and does not apply to older vehicles.
- Many car manufacturers have already introduced TPMS to their vehicles ahead of the 2012 legislation change.
- Renault Peugeot and Citroen have fitted TPMS to some models since 2000.
- More and more cars now have TPMS already fitted. Showrooms are full of TPMS compliant cars.
Why do we need to Service Sensors?
When a tyre is replaced or a puncture repaired on a vehicle without TPMS, it is normal practice to replace the rubber valve. With a TPMS sensor it is also important to replace the rubber sealing grommet which deteriorates just like the rubber valve. At the same time as replacing the rubber grommet, it is good practice to replace other parts too.
The Metal Sealing Washer (if fitted) often becomes distorted, replacing this ensures a good seal when re-assembling the sensor.
The Outer Collar is replaced because it becomes metal fatigued, and sometimes badly corroded. This metal fatigue can often make the outer securing collar crack and sometimes this will fall off completely.
The Core is replaced to create a good airtight seal in the sensor internally. Only Nickel plated cores should be used in Metal Valves.
The Cap is replaced with a new pressure cap. Again the rubber washer in the old cap deteriorates, replacing the cap helps keep the sensor airtight and free from debris, or fluids that might affect the operation of the core.
Best Practice in the Tyre Bay
When a TPMS car arrives in the tyrebay we should physically check the sensor valve stem for signs of excessive corrosion or damage, then the sensor should be checked electronically using a trigger tool to capture the sensor data. This will tell the technician that the sensor is working correctly and if the battery is low. We can then discuss what is required with the customer prior to work being done.
Each time a tyre is replaced the sensor should be serviced and parts replaced, generally the outer valve stem collar, the rubber grommet, the core and the cap should be replaced. The outer valve stem collar has to be tightened to the correct torque to ensure a good airtight seal using a special low torque Torque Screwdriver. The valve cores have to be correctly torqued too and again there is a special pre-set torque core driver used for this. Some sensors use a special rubber valve stem, and the service part is a new rubber valve stem.
Once the sensors have been serviced or replaced we need again to electronically check the sensors with a diagnostic tool, many cars have to have this sensor data downloaded into the cars ECU via the OBDII socket if we replace a sensor of change the position of the wheels. The ATEQ VT55 OBDII can be used to simply and quickly download this data to the ECU. We can also then record the sensor data on a file in the POS system or print out a copy as a record for the customer.