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Troubleshooting Garmin Sonar Black Boxes

Garmin sonar black boxes (such as the GCV™ sonar modules, GSD™ sonar modules, and the GLS™ 10 sonar module), have an LED status light that indicate if an error has taken place and what has caused it.

NOTE: If the error light or chartplotter indicates that a transducer is not detected, see Garmin Marine Device Shows No Sonar Option or Depth Reading for troubleshooting instructions. 


Power issues

For instructions to troubleshoot power issues, click the steps below:

Check the fuse

Check for a blown inline fuse on the red wire of the power cable. If it is difficult to see whether the wiring is intact, connect a multimeter to both ends of the fuse, and measure for resistance. A good fuse would show close to 0 ohms on the multimeter.

Some multimeters have a continuity setting to check for blown fuses. These multimeters will emit an audible tone if the fuse is working.


Check the power supply

  • Charge the battery fully, then remove the battery from the charger and wait 12 hours before testing the battery with a voltmeter. The engine must not be running while testing the battery

    • The ideal voltage is over 12 V. If the voltage is lower, the battery does not have enough power to run the sonar module. Replace the battery

    • If the sonar module connects to a switch, fuse panel, or wire block, temporarily connect the power cable directly to a fully charged 12-volt battery. Check original wiring of the panel, circuit breaker or switch. Replace the switch, board, or circuit breaker if visible damage is present

    • Due to the power requirements of the LiveScope system, if there are multiple devices connected to the power source remove all other devices except for the Chartplotter and LiveScope system and test if the black box will power on


Check power cable and wiring

  • If extension wires are being used between the module and power source, ensure that the correct gauge is used for each wire. Lower gauge numbers allow for a greater amount of power to be transferred. See Wire Extension Table for Garmin Marine Chartplotters and Fishfinders

  • Inspect the power cable's wiring system for any loose or damaged wires, faulty termination points, incorrect terminals

    • If the wire is corroded at the termination points, cut the ends of the wire at both power and ground, strip back the sheathing, and rewire the new ends. If this is not possible, replace the power cable

  • Check the brass contacts on the power cable connector head and the module's power port for tightness and corrosion

    • If there is light corrosion on the brass contacts, this can be cleaned with a brush and dielectric grease

    • If there is extensive corrosion on the power cable connector head, the corrosion may have extended into the cable itself. The power cable will need to be replaced

    • Extensive corrosion on the module's power port indicates possible damage to the sonar module. The module will need to be replaced

  • Check the voltage on the power cable connector head using a voltmeter or multimeter. The preferred voltage is over 12 V; a lower voltage may not be sufficient to power the module. If no voltage is detected, or if the voltage is significantly lower than that of the battery, replace the module's power cable

    • If using a multimeter, set it to DC. Consult the multimeter's owner's manual if unsure of where this setting is on the multimeter


Check for voltage drop

The module draws more power (known as amperage) when starting up, then needs less power to run after starting. There may also be insufficient amperage if the module is connected to a cranking battery and loses power when the engine starts or speed increases.

Checking for voltage drop will show whether the module is receiving insufficient power to startup:

    1. Turn off the power source and disconnect the power cable connector head from the sonar module

    2. Connect the voltmeter or multimeter to the wire ends of the power cable, where wires connect to the power source

    3. Turn on the power source

    4. Watch the voltage and reconnect the power cable to the module

      • If the voltage drops, there is insufficient power going to the module. Connect the module to a different power source

      • If the voltage remains steady, contact Product Support for further assistance


Marine Network issues

NOTE: ALL devices connected to the Garmin Marine Network must be connected to the same ground. If multiple power sources are used for Garmin Marine Network devices, all ground connections from all power supplies must tie together using a low resistance connection or tied to a common ground bus bar, if available; see, Garmin Marine Network Considerations

If the error light indicates a Marine Network issue, make sure the sonar module is connected to a chartplotter using a Garmin Marine Network cable. 

Check whether the chartplotter detects the sonar module over the Garmin Marine Network:

  1. On the home screen, select Settings

  2. Select Communications

  3. Select Marine Network or Garmin Marine Network

  4. Select Device List

If the sonar module displays in the Device List, check the cables and marine network ports for corrosion.

If the sonar module does not appear in the Marine Network device list, follow the troubleshooting steps below:

  1. Update the chartplotter system software. See for instructions

  2. Inspect both ends of the marine network cable for corrosion or damage

    • If the cable ends are new or recently replaced, refer to the Marine Ethernet Installation Instructions to ensure proper installation

    • If possible, check the cable for continuity using a network cable tester or a multimeter. If there is no continuity, repair or replace the cable

      • To purchase a new marine network cable, search for the sonar module model on garmin.com, click Accessories, then click Garmin Marine Network

  3. If the chartplotter or sonar module has multiple marine network ports, test the marine network cable with each port to see if the module appears on the Marine Network device list. If it does, a specific Marine Network port may be defective

Using a GMS™ 10 Network Port Expander

If using a GMS 10 Network Port Expander, check the LEDs above the ports to which the chartplotter and module are connected. If the LED above the cable for the sonar module is not blinking, meaning that no network connection is detected, connect the marine network cable to a different port on the GMS 10.

If the sonar module is detected over the Marine Network when connected to another port, the original port may be defective. Replace the GMS 10.

If none of the ports' LEDs light up when any marine network cable is connected, contact Product Support to replace the GMS 10.


If the sonar option on the chartplotter does not display after following these troubleshooting steps, contact Product Support.

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