Tyre pressure warning light on (TPMS): causes and what to do

The most common cause of a TPMS warning is one or more tyres that have dropped below the vehicle manufacturer's recommended pressure threshold, which is typically triggered when pressure falls 25 per cent or more below the specified figure. Tyres naturally lose a small amount of pressure over time, approximately 1 to 2 PSI per month, so a tyre that was correctly inflated three or four months ago may now be low enough to trigger the sensor. A slow puncture, where a small object such as a nail or screw has penetrated the tyre but the air loss is gradual over days rather than immediate, is another frequent cause. The TPMS light may come on in the morning after a cold night (when tyre pressures are lower) and go off once the tyres warm up, which is a reliable indicator of a tyre that is borderline low rather than flat.

Typical repair cost: Tyre inflation at a garage or petrol station: free to £5. Slow puncture repair (plug or patch): £15 to £30. Tyre replacement if the tyre is too damaged to repair: £60 to £200 depending on the tyre size and specification.

Each wheel on a TPMS-equipped vehicle contains a small electronic sensor screwed into the valve stem or banded to the wheel that measures tyre pressure and transmits the reading wirelessly to the vehicle's TPMS control module. These sensors can fail for several reasons: corrosion at the valve stem (particularly on alloy wheels in winter road salt conditions), physical damage during a tyre change if the sensor was struck or dropped, or an internal electronic fault. On indirect TPMS systems, which use the ABS wheel speed sensors to infer pressure from wheel rotation speed rather than dedicated pressure sensors, a fault code can also be triggered by an ABS sensor failure. A faulty sensor will often cause the TPMS light to illuminate even when all tyres are correctly inflated.

Typical repair cost: TPMS sensor replacement (direct system): £50 to £120 per sensor including fitting and programming. TPMS sensor valve stem replacement (if just the stem is corroded): £20 to £50. TPMS system recalibration (indirect system): £30 to £60.

A sudden puncture or tyre blowout will cause a rapid and significant pressure drop that the TPMS sensors detect immediately. A blowout, where the tyre fails suddenly and loses pressure in seconds, is the most dangerous scenario, as it can cause a sudden pull to one side and loss of vehicle control. Modern run-flat tyres are designed to remain functional at zero pressure for up to 80 kilometres at speeds not exceeding 80 km/h, but conventional tyres driven on when flat rapidly destroy the tyre sidewall and can damage the wheel rim. On vehicles without run-flat tyres, the TPMS light combined with a sudden change in handling, a loud bang, or a strong pull to one side indicates an immediate puncture requiring the vehicle to stop.

Typical repair cost: Puncture repair (if caught early and the tyre structure is undamaged): £15 to £30. Tyre replacement (if the tyre has been driven on flat or is blowing out): £60 to £200 for the tyre itself. Wheel repair if the rim has been damaged: £60 to £200.

Tyre pressure varies with temperature: for every 10 degree Celsius change in air temperature, tyre pressure changes by approximately 1 PSI (0.07 bar). This means a tyre inflated to exactly the correct pressure on a warm summer afternoon may drop enough during a cold winter morning to trigger the TPMS warning. This is particularly common at the start of winter when temperatures drop suddenly, and many drivers find the TPMS light appears on the first cold morning of the year even though tyre pressures were correct a few weeks earlier. The light will often go out on its own once the tyres warm up after a few minutes of driving, but this does not mean the tyres do not need inflating; it means they are borderline low.

Typical repair cost: No repair needed. Tyre inflation at a petrol station: free to £5. Checking and adjusting all four tyres seasonally costs nothing if you have your own gauge.

The sensors in a direct TPMS system contain small non-replaceable batteries with a typical lifespan of 5 to 10 years, depending on how frequently the sensor transmits data. As the battery approaches the end of its life, the sensor begins to transmit intermittently or stops transmitting altogether, causing the TPMS warning light to illuminate. Battery failure is particularly common on vehicles aged 7 years or more and is often flagged by a garage when tyres are being changed, because the sensor must be removed from the wheel to replace it. On vehicles where tyres are replaced frequently (high-mileage or enthusiast vehicles), sensors may need to be replaced before their batteries fail from the repeated removal and reinstallation process damaging the sensor body.

Typical repair cost: TPMS sensor replacement (including programming to the vehicle): £50 to £120 per corner. Many garages recommend replacing all four sensors at once if one has failed due to age, as the others will follow shortly. Full set of four sensors: £150 to £400.