2006 Mercury Sable check engine light

The check engine light in my girlfriend's car turns on from time to time and then shuts off after a few days. She is convinced that it has something to do with the way I drive, since it doesn't (as far as I know) turn on when she drives. Can driving habits cause this? We are both careful drivers, and this happens only once every couple of months - much less often than I drive the car.

Thanks,
John