If you have air conditioning fitted to your 451 Fortwo, it is a good idea to check the drain pipe yearly.
The drain pipe is hidden under the carpet to the side of the centre console. It runs towards
the back of the car for 8" and then into the battery tray (LHD cars may be different).
The best course of action is to check under your carpets regularly for any moisture.
Feel under the footwell carpets on both sides for a wet carpet backing. There is no point feeling
the visible side for wetness as the carpet is plastic backed so water won't seep through.
This was obviously designed so that water from wet shoes wouldn't soak through to the foam.