Had my TPMS warning light come on yesterday near the end of a 120 mile journey. On checking at a garage air pump all the tyre pressures were the same, though slightly under recommended pressure. At the correct pressure the warning light stayed on so looked through the manual for ages until I found where the TPMS reset button was located.
If the Tyre Pressure Monitor light comes on, and once you've properly adjusted the air in your tyres (obviously checking for punctures or damage), you must reset the warning light by pressing and briefly holding the TPMS button which is located to the right of the steering wheel and is clearly marked (next to the istop button).
Most of you may already know this, but it had me foxed for a while.