According to edmunds, for 2004, the Sentra receives some exterior changes that include new front and rear fascias and a revised hood. Inside, the Sentra gets a new trip computer, which is standard on the SE-R, Spec V and 2.5 S.
There is also an upgraded Rockford Fosgate stereo. The Sentra SE-R Spec V gets a new Brembo brake package, seats from the Skyline, new interior fabric and two new exterior colors -- Volcanic Orange and Sapphire Blue.
Download here 2004 Nissan Sentra Owners Manual