According to edmunds, fresh front-end styling, a Limited Edition Option Package for GXE models and some new paint colors constitute the changes for 1999.
Though it is refined, roomy and reliable, Nissan's smallest sedan has not been the success Nissan hoped for during the past three years. Offered in three trim levels (XE, GXE and SE-L), the current generation Sentra debuted in 1995 and has failed to become a hot seller because of the car's frumpy looks. In defense of its styling elements, Nissan attributes its low 0.33 coefficient of drag to the car's high rear decklid, steeply raked windshield and low hood line. The design also provides enhanced visibility and a spacious trunk. This year, at least Nissan gave the car's front-end a once-over, adding a new headlight treatment, grille and front fascia.
Download here 1999 Nissan Sentra Owners Manual