One or more of your tyre pressures could be close to the low-pressure threshold. Overnight when your tyres are cold, the pressure will be at its lowest, bringing the pressure close to or below the 20% minimum pressure allowance – switching the TPMS warning light on. Once you start driving, however, your tyres will warm up, and the pressure will subsequently increase, turning the warning light off. Check your tyre pressures before driving to ensure they are at the correct pressure.