My daughters car is an 06 Mercury Mariner v6 all wheel drive. The O/D off light has started coming on while it is driven at extended freeway speeds. If the car is shut off for a time the light will not come on until it has been at freeway speed for a time. She has been driving it around town and to work and the light has not come on. The fluid seem to be filled correctly. Can anyone tell me what the situation making the light come on would be? Might this be a common Mariner problem? Thanks Dan