Most sounder problems reside in your transducer, not the sounder. Since transducers can't easily be pulled, normally you can borrow a transducer from a dealer or marina and connect it to your sounder and hang it over the edge of the boat for testing. You could check your temp sensor of the transducer with a multi-meter (instructions on this forum in another thread). Before sending in the sounder for testing, you could ensure that user settings haven’t gotten out of whack. You can reset the sounder settings and the sounder itself.
1. (MENU - FISHFINDER icon - DFF tab - RESET DEFAULT SETTINGS at bottom of page)
2. (MENU - SYSTEM icon - DFF tab- RESET DEFAULT SETTINGS at bottom of page)
3. (MENU - SYSTEM icon - MEMORY tab - Select sounder and pick reset to FACTORY DEFAULT in the sounder area)
After clearing everything put the sounder in duel range, auto cruising, and auto range.
Allow the sounder to get an established bottom and if not showing depth, try adjusting the BL lower unit depth shows up.
If the issue still is present, send the sounder box into the service center for evaluation. If it tests good at the service center; then your transducer might need to be tested or replaced by your dealer.