Tyre pressure (TPMS) warning light on

This is the first hypothesis to check, and the most important for safety: the TPMS light is right, one or both tyres are genuinely under-inflated. The usual causes are the same as any classic pressure loss: a slow puncture (a small nail or screw lodged in the tread, a perforation leaking slowly), a valve letting air escape (aged seal, cracked valve body, missing cap letting dirt in), a tyre bead no longer perfectly sealed on the rim (buckled rim, impact), or simply the natural, slow decay of pressure over time if the check has long been neglected. The deciding clue: a reliable gauge measurement, cold, confirms a pressure below the manufacturer's value. Correction principle: identify the cause of the drop (puncture search with soapy water, visual check of valve and bead), repair or replace what's leaking, then re-inflate to the exact cold value. It's a basic job for a simple re-inflation, intermediate if a puncture repair or valve replacement is needed. After correction, the light usually goes out on its own after a few minutes of riding, once the sensor measures a normal pressure again.

Each TPMS sensor carries its own miniature battery, sealed and not separately replaceable: when it runs down (generally after 5 to 8 years depending on use and brand), the whole sensor must be changed, there's no simple battery swap. Corrosion is the other great enemy: these sensors are fitted inside the wheel or on the valve, permanently exposed to damp, road salt and spray, which attacks their electronic contacts over time. A faulty sensor gives obviously wrong information: pressure displayed as zero or dashes, a value jumping inconsistently from one moment to the next, or a signal lost while riding then found again later. The deciding clue: a pressure measured with a gauge perfectly correct on both wheels, while the dashboard display shows clearly aberrant or absent values. Replacing a TPMS sensor usually means removing the tyre (the sensor is fixed inside the rim, on the valve), so tyre-changing tools and a balancing machine: it's an intermediate-level job, usually entrusted to a tyre fitter or an equipped professional rather than bodged in a garage. A universal kit costs around €60-120, an OEM sensor rather €100-150 each.

Each TPMS sensor has a unique radio ID, registered in the bike's receiver unit to know which wheel matches which sensor. After a tyre change by a fitter who doesn't know the bike-specific procedure, a wheel replacement, or sometimes even a simple 12 V battery change (which can wipe the pairing memory on some systems), the receiver no longer recognises the sensor(s): the light stays on, or the display shows dashes continuously, even though the sensor itself works perfectly and the pressure is fine. It's a harmless and common cause right after tyre or wheel work, not to be confused with a real sensor failure. The deciding clue: the light appeared right after a tyre change, a wheel or battery job, and the pressure measured with a gauge is perfectly correct. Correction principle: follow the manufacturer's relearn (reset) procedure — often an ignition/key sequence or a dedicated button, sometimes a diagnostic tool for more complex systems — to re-register each sensor's ID in the unit. It's a basic to intermediate job depending on the model, usually described step by step in the owner's manual.