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NMEA 2000 Troubleshooting on Garmin® Marine Devices
If the Garmin® chartplotter is not recognizing part or all of the devices connected to the NMEA 2000 network, check that the NMEA 2000 network contains the correct number of T-connectors, terminators, and cables and is configured correctly. A simple NMEA 2000 network consisting of two devices should include everything in the picture.
This image shows a NMEA 2000 backbone; a series of T-Connectors joined together with terminators on both ends, two drop cables, and an NMEA 2000 power cable.
One NMEA 2000 T-Connector for every device and accessory connected to the network
One NMEA 2000 T-Connector for the NMEA 2000 power cable
One NMEA 2000 Drop Cable up to 6 m (20 ft) can be used as a backbone cable or a drop cable. A cable longer than 6 m (20 ft) can be used as a backbone cable only
For in-depth information on how to create a NMEA 2000 network, review the Technical Reference for Garmin NMEA 2000 Products Installation Instructions.
Viewing the NMEA 2000 Device List
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.
Testing the NMEA 2000 Continuity
Below are the pin assignments for a female NMEA 2000 connector.
1 TSP = Twisted pair
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
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
Disconnect the yellow power cable from the backbone
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
Other Considerations for Troubleshooting NMEA 2000
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
- 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