If it's a Lowrance, and it says "GPS Module not responding" it is a power issue, "both" the GPS and Sonar have to be connected to power, it should say that in the manual.
If it's a new HD unit I don't know if GPS needs seperate power lead and don't know much at all about them..
I have a spare (of course) Lowrance GPS module if yours is an external unit that you can plug in and see if it is the module itself before buying another module..
I HAVE HAD PROBLEM WITH MINE. GO TO LOWRANCE WEB SITE AND GET TROUBLE SHOOT DIAGRAM. I DID MINE, GOT MODUL CHECKED, GOT NEW CABLE, THINK UNIT NEEDS TO BE SENT BACK. IF YOU HAVE A QUESTION FEEL FREE TO CALL ME. 435 668 6696