What is TPMS?

TPMS systems are now mandatory on all newly registered vehicles in the EU (since November 2014). They are fast becoming a vital part in maintaining safety on the roads. The system works by monitoring the pressure (and sometimes temperature) within each of the vehicle’s tyres. TPMS stands for Tyre Pressure Monitoring System, a new safety feature which continuously 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. Tyre bays and workshops can check tyre pressure using diagnostics tools, reading the pressure from OEM or aftermarket sensors.

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.

What is Direct TPMS?
Each wheel & tyre of the vehicle has a sensor fixed (usually within the valve) to monitor the changes in pressure from the tyre. Tyre pressure sensors often also measure temperature. Each sensor sends its signal to the receiver inside the vehicle using a wireless connection. In Europe the transmission frequency is 433Mhz. If low pressure or a leak is detected (generally 25% less than normal operating pressure), the driver is alerted by the in-car system and generally the deflated tyre is identified.
• Direct TPMS is very accurate measuring to 1 or 2 psi.
• A puncture after parking is immediately identified.
• Sensors send their signals approximately every 30 seconds, when parked they transmit every 20 to 30 minutes. At 25 kph the sensor switches back on to transmit every 30 seconds.
• Sensors have an approximate life of 5 years or 160,000 km.

What is Indirect TPMS?
• Indirect TPMS is generally fitted to a vehicle that has had fitted or can be fitted with run flat tyres. This is because it is difficult to see or feel deflation in this type of tyre.
• Indirect tyre pressure monitoring systems do not use pressure sensors to monitor tyre pressure, they work from the ABS or speed sensors on the vehicle.
• Indirect systems monitor tyre pressure by assessing the rotational speeds of each tyre, and work on the premise that an under-inflated tyre has a slightly different diameter than a fully inflated tyre. An algorithm is used to assess the differences in wheel speeds.
• The under-inflated tyre would therefore rotate at a different speed than the correctly inflated one, causing a tyre pressure warning. The deflated tyre is not identified, the driver has to check all 4 tyres

Negative Aspects of Indirect TPMS
• The system is not very accurate.
• When tyres are re-inflated, the system needs to be re-calibrated.
• When tyre positions are changed, the system needs to be re-calibrated.
• When the tyres are replaced, the system needs to be re-calibrated.
• The system can be re-calibrated by the driver without first ensuring that the pressure is correct in all tyres.
• A puncture after parking is not immediately identified.

The TPMS Legislation 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.