LOw Oil Pressure warning.on all cold starts on 2005 Mercury Montego

I'm getting Low Oil pressue warning on all cold starts.....I just had car serviced for oil change, replaced air and gas filter.

Asked by for the 2005 Mercury Montego
Very important to check your oil at least - make sure it is full. Other than that - the switch that tells the car you have low oil pressure could be faulty, or the vehicle truly has low oil pressure and requires a diagnosis. The only real way to know is to have a manual oil pressure gauge installed to check the actual pressure.