How do you check leveling sensor? The rear of the car rides low on 1997 Cadillac Seville SLS

The car rides low but when i had the car in for oil change it leveled after coming down from the lift. After driving about 9 miles it rides low again.

Asked by for the 1997 Cadillac Seville SLS
it is called a height position sensor. have it checked by someone who is familiar with the system.