If memory serves: It is to turn on the fuel flow feature if you purchased fuel flow at a later date.
 
How to activate?

Kevin, How does one activate that feature? I just installed the transducer but do not know how to activate. Ideas?
 
Kevin, How does one activate that feature? I just installed the transducer but do not know how to activate. Ideas?

If you purchased the transducer with your EIS it should be already activated (mine was). Otherwise, you'll need to call GRT and give them your serial # and they can generate the code.