Tyre Pressure Warning Light (TPMS) — What It Means

The TPMS (Tyre Pressure Monitoring System) warning light — shaped like a cross-section of a tyre with an exclamation mark — means one or more tyres has dropped significantly below the recommended pressure.

Check all four tyre pressures immediately. A tyre that's significantly underinflated is dangerous — it handles poorly, can overheat and blowout at speed, and wears unevenly. Tyre pressures should be checked monthly and always when cold (before driving).

Where to find your correct tyre pressures:

The recommended pressures for your specific car are shown on a sticker inside the driver's door jamb, inside the fuel filler flap, or in your car's handbook. They're different for front and rear, and often different for loaded vs unloaded conditions.

Why pressures drop:

Natural diffusion — tyres lose approximately 1 PSI per month through normal diffusion of air through the rubber. This is normal and why monthly checks are important.

Temperature changes — tyre pressure drops approximately 1 PSI for every 10°F (5.5°C) drop in ambient temperature. The TPMS light often comes on during the first cold morning of autumn — not because you have a puncture, but because the temperature dropped overnight.

Puncture — a slow puncture or nail in the tyre causes gradual pressure loss. Inspect the tyres visually and look for any obvious damage.

Faulty TPMS sensor — each wheel has a battery-powered sensor that transmits pressure data. The batteries last 5–10 years and then the sensor needs replacing (£40–80 per sensor including fitting, as the wheel must be removed and the tyre partially dismounted).

After the light comes on with correct pressures:

If you inflate to the correct pressure but the light stays on, the system needs resetting. On most cars there's a TPMS reset button (consult your handbook) or it resets automatically after driving at speed for a few minutes. If it still stays on after reset, have the sensors checked.