Tyre Pressure Monitoring System

Although it has been available on some vehicle marques since the mid-1990’s, from 1st November 2014, it will be a legal requirement for all vehicles coming into, or being produced in Europe to be fitted with a TPMS (Tyre Pressure Monitoring System).

What are the benefits of TPMS?

TPMS sensors constantly keep track of tyre pressures, reducing the risk of blow outs as a warning lamp indicates when there may be a problem about to arise; this provides the driver of the vehicle an ample amount of time to stop and assess the situation before anything severe could occur.

Benefits of TPMS

Other than the risk of blow-outs, further advantages of having the correct tyre pressures are:
  • Increases the tyre’s life span
  • Significantly decreases fuel consumption
  • Shorter stopping distances when braking
  • Lower risk of aquaplaning
Incorrect Tyre Pressures

Types of TPMS

There are two main types of TPMS system currently active in today’s market, Direct and Indirect, with each utilising different operational functions


Indirect

Indirect TPMS systems combine the Anti-lock Brake System (ABS) and the Electronic Stability Control (ESC) of the vehicle to estimate the relative tyre pressures. If a tyre’s pressure becomes low it will roll at a different wheel speed than the other tyres. This information is detected by the car’s computer system, which triggers the dashboard indicator light. Although commonly found on BMWs and Minis, Indirect TPMS has a tendency to be inaccurate as a warning signal may not be given if the system is calibrated incorrectly, or if all four tyres are leaking air at the same rate. Environmental factors such as road and weather conditions may also result in a false reading. As Indirect TPMS functionality is based upon an estimation of ABS and ESC systems, no further work is required to service this system. Once a tyre is changed the system can be reset as per the manufacturer’s guidelines.

Direct

Direct TPMS uses wheel mounted sensors which transmit data directly to the driver via the dashboard. The warning light / indicator is designed to activate when there is a minimum 20% drop in pressure (6-7 psi). The sensors all have unique codes to prevent picking up signals from other vehicles and in addition to allow each sensor’s wheel position to be recognised by the vehicle’s computer system.

MOT legislation

TPMS is now part of the annual MOT test, and applies to all newly registered cars from January 1st 2012. This means that a car with a faulty TPMS will fail the vehicle test from January 2015.
Please remember this regulation only applies to new vehicle models manufactured after January 2012 and all vehicles produced after 1st November 2014.

TPMS Warning Light
Tyre Pressure Monitoring System

How the sensor operates

Each sensor relays tyre related data via radio transmission at a frequency of 433MHz to the vehicle’s engine control unit (ECU). This data can include tyre pressure, tyre temperature, battery status (dependant on sensor model) and the unique sensor identification number.
Here is an example of a typical Direct TPMS sensor:

TPMS Valve