NMEA 2000 Troubleshooting on Garmin® Marine Devices

If a NMEA 2000 device is connected to the network but is not turning on or displaying / sharing data, check the NMEA 2000 device list to see what shows as connected. 

From a current model GPSMAP®:

Select Options > Communications > NMEA 2000 Setup > Device List to view connected devices. 

From a Legacy GPSMAP unit or ECHOMAP™:

Select Settings or Configure > Communications > NMEA 2000 Setup > Device List to view connected devices. 

A list of all devices and accessories on the NMEA 2000 network should be listed. If the devices are missing from the list, troubleshoot the T-connectors and drop cables. Swap the NMEA 2000 drop cable of the device not seen on the network to a known working T-connector. Check the NMEA 2000 device list. If the device does not show on the list, follow the testing instructions below to try and locate any faults. 

Below are the pin assignments for a female NMEA 2000 connector.

PIN # NAME PAIR WIRE COLOR WIRE SIZE 1 SHIELD DRAIN BARE 22 AWG 2 CAN-S POWER + 12 VDC RED 22 AWG (TSP)1 3 CAN-C POWER GROUND BLACK 22 AWG (TSP)1 4 CAN-H SIGNAL WHITE 22 AWG (TSP)1 5 CAN-L SIGNAL BLUE 22 AWG (TSP)1

¹ TSP = Twisted pair

1. Test for DC voltage on the +12v and Ground pins at the female end of every drop cable

• • If a reading 12v or greater is not present, check your NMEA 2000 fuse and power source

  • If voltage is present at the end of every drop cable, move on to the next step

1. Test for resistance between the Ground and Shield pins. There should be very little resistance (close to 0 Ohms) because the bare shield wire of the power cable connects to the ground

2. Disconnect the yellow power cable from the backbone

3. Test for resistance (Ohms) between the Can-H and Can-L Pins at the female's end of every drop cable

• • The reading should be close to 60 Ohms

  • If the resistance reading is 120, only one terminator is connected to the network. Two terminators are required

  • If the resistance reading is very high, there are no terminators on the network or a break in one of the network components

  • If the reading is 40, there are 3 terminators on the network. One needs to be removed

Each NMEA 2000 backbone should have only 1 12VDC power source connected to the NMEA 2000 network unless one of these applies:

• The single NMEA 2000 network is very large, in which case a second 12VDC power source can be added; but there must be a NMEA 2000 Power Isolator installed somewhere between the 2 power cables

• If the vessel has 2 or more NMEA 2000 networks there will be at least 1 each 12VDC power source for each separate NMEA 2000 Network

NOTE: For questions about a factory-installed NMEA 2000 network that is not directly addressed in the NMEA 2000 Technical Reference Guide for Garmin Marine Devices; contact an authorized Garmin installer or certified NMEA 2000 installer.

Select this link NMEA 2000 Technical Reference Guide for Garmin Marine Devices, enter "Power Isolator" in the Manual search bar for specific information

• NMEA 2000 Power Isolators are used to isolate 2 or more NMEA 2000 powered networks from each other

• The Power Isolators allow the NMEA PGN communication to pass between the networks, but will not allow the power to be transferred or used in the other NMEA 2000 network beyond the Power Isolator 

• Some Fusion® stereos and other NMEA 2000 devices can provide an unintended second source of power to the NMEA 2000 backbone

  • This can cause information to be lost or even damage equipment, so always check the owner's manual of any device being connected

• Fusion stereos have a menu option to turn NRX Power off

  • The NRX POWER option should be enabled only when the stereo and up to 3 MS-NRX300 remotes are the only devices connected to a network 

    • From the Fusion stereo select Menu> Settings > Power Options > NRX Power > Off or On depending on installation

  • See Connecting a Fusion® Stereo to a Wired Remote for more information on Fusion stereo and remote connections