Actually the module is for mapping a planet otherwise Tyres is correct.
The one that scans systems is built in, it does have to be assigned to a fire group.
You need to be in Analysis mode to use either of them.
After honking the system slow down to minimum Supercruise speed to use the Frequency Scan System or FSS to discover the details of the bodies in the system. Many bindings to be checked to see what you had doing which.