Tyre Pressure Monitoring System (TPMS) Explained

Tyre Pressure Monitoring Systems are electronic systems built into vehicles to primarily alert the driver to a low tyre pressure situation. Many vehicles now very sophisticated and have individual sensors mounted within the wheels that transmit the exact pressure in the tyre to the vehicle ECU. TPMS report real-time tyre-pressure information to the driver of the vehicle, via either a gauge, a pictogram display, or a low-pressure warning light. Should this pressure fall below a pre-determined threshold, the vehicle will display a warning on the dashboard.

TPMS has now been around on regular cars for well over 15 years, but relatively recent changes to legislation meant that from November 2012 all new car models had to be equipped with TPMS and from November 2014, every single newly registered car had to be fitted with a tyre pressure warning system as standard. Importantly, the TPMS system for cars registered from 1st January 2012 is tested as part of the MOT. If the system is not working as designed, there will be a flashing TPMS warning light on the dashboard when the electrics are initially switched on. This light will eventually go solid, usually after a minute or so, but in this situation the system would fail the MOT. Therefore it is important that the pressure warning system is regularly checked for faults.

With systems that have individual pressure sensors in the wheels, referred to as DIRECT TPMS, the sensors themselves have a limited life, depending on how they are maintained:

• Sensor Batteries: The sensors are battery powered and ultimately once the battery is completely depleted the sensor will stop working. Unfortunately, due to the conditions in which these sensors exist, the sensor units have to be completely sealed so once the battery does fail the sensor will need to be replaced. Battery life can vary, as more miles driven equates to the sensors being active for longer, thus using up more battery. On average we would expect a TPMS sensor battery to last anything between 4 & 8 years, though due to the large number of different sensors using different components, these figures can vary. Our staff have state of the art electronic equipment to test your sensors at the wheel side, determining the status of the sensors, including the tyre pressure as well as having an indication of the state of the internal battery.

• Valve Stems: In the UK, all common DIRECT TPMS sensors are mounted at the base of the valve stem which is there to allow you to inflate your tyres. Although many of these valve stems are now made from rubber, especially those found on the new Ford models, there are also a wide range of sensors that utilise an aluminium valve stem. TPMS rubber valves are slightly different to standard rubber valves as they are attached to their respective sensors but they should ideally be handled in the same way as any standard rubber valve would be. Rubber is a perishable material and valve stems are exposed to the elements 24/7, also the valve is key to sealing the air in the tyres as well as allowing you to put air into the tyres, so it is recommended that the valves should be replaced whenever a tyre is replaced or repaired. With the aluminium style of valve, these come equipped with a rubber seal that should also be regularly replaced. However, due to additional corrosion issues that can affect metal valves it is recommended to replace all of the removable components of the valve stem as a minimum with each tyre replacement / repair. In some cases a full valve stem assembly may be required to maintain the correct function of the sensor. Our on site experts can inspect and advise on the best course of action on a case by case basis.

• Metal Valve Caps: Unfortunately many of the metal valve caps that are available to buy are not compatible with the TPMS valve stems. Fitting metal valve caps can more often than not result in the cap becoming seized to the valve making it impossible to remove without damaging the valve stem. In some cases, the valve stems can not be replaced separately to the sensor unit and a complete sensor replacement may be required. Our staff will discuss the various options available to you if they find metal valve caps fixed to your valve stems.