1999 Saturn Sedan P1620 trouble code

The light being on with the bottle full first check ur back up fuse in ur underhood junction block aka fuse box that fuse runs that circuit. Next un plug coolant bottle check terminials to bottle then jump the connector across the terminals and start car if the light goes off after a coulpe of mins its a bad coolant level sensor if the light doesnt go out then u have a problem with the circuit. Good luck let me know how it goes.
Louie