I have a comon Garmin GPSmap 923xsv plotter/MFD. And I am not able to use this as a GPS with Cerbo. I can see units from my NMEA2k network on the cerbo, but for some reason the GPSmap apears as a “virtual” device (?). And when I use the v1 interface and select GPS, I dont see my unit. This unit is the current GPSmap, and is running the latest Garmin firmware.
Just to be sure. According to the manual this is supose to work. Anyone got it working? GPS to VRM over nmea2000?
When the NMEA 2000/STNG network has GPS data, the GX device sees this as a GPS source and is able to use the GPS position in VRM.
Hi @havard , the right documentation is this one:
If it will work depends a bit on what GPS data is sent exactly by that GPSMAP.
Do you happen to have Actisense USB dongle to take a look and share for example a screenshot?
Yes, I have seen that documentation as well.
I dont have Actisense USB dongle, but do have signalk with NMEA2000 interface. I can see if I can dig out what the GPS broadcast look like. But I assume it is according to this:
NMEA 2000 Navigation Information
I see that PGN 129025 is not i the list from Garmin. PGN 129029 is in the list from Garmin, but is listed as optional from Victron.
Could it be that Cerbo is expecting to se PGN 129025, but the Garmin is sending this position data on PGN 129029?
@mpvader is the information above helpfull? Could it be the case that the cerbo is looking for the “wrong” pgn?
@mpvader does the gps over NMEA need to work go get speed in the boat page to work?
Hi @havard ,
is the information above helpfull? Could it be the case that the cerbo is looking for the “wrong” pgn?
Yes, helpful. Not looking for the wrong PGN, but probably too restrictive with regards to device class and function. We’ve added looking into this to the todo list, and expect to be able to fix it. That will take a while though - the person good at this has quite a list of tasks. Few months minimum I’m afraid.
does the gps over NMEA need to work go get speed in the boat page to work?
For the speed to work in the boat page, the GX needs to get speed from a GPS. Can be over NMEA2000, but also over a simple USB connected GPS
( #885 )
Ok. Thanks for the feedback. Then I won’t hold my breath…
@mpvader it sounds like @havard 's issue is the same as mine here: Cerbo GX - GPS from NMEA woes
Do you have any updated ETA for when this might be able to be fixed?
no eta, sorry.
Request for GNSS Acceptance Support for Cortex AIS/VHF Device on Cerbo GX (NMEA 2000)
Hello Victron Support,
I am requesting assistance regarding GNSS data acceptance on my Cerbo GX when connected to a Vesper/ Garmin Cortex AIS/VHF system over NMEA 2000.
System Overview
- Cerbo GX running latest firmware
- Connected to NMEA 2000 backbone via VE.Can → NMEA2000 Micro‑C cable (ASS030520300)
- Cerbo GX successfully detects the Cortex device on VE.Can (“CORTEX [693115] – Online”)
- Garmin chartplotter on the same NMEA 2000 backbone receives full GNSS data from Cortex
- VRM Portal shows no GPS position from Cerbo GX
- Cerbo GX GPS menu remains hidden
Cortex GNSS PGNs (confirmed from Garmin documentation and live network traffic)
Cortex broadcasts the following PGNs on NMEA 2000:
- 129025 – Position, Rapid Update
- 129026 – COG/SOG, Rapid Update
- 129029 – GNSS Position Data
- 127250 – Vessel Heading
- 127258 – Magnetic Variation
- 128259 – Speed, Water Referenced
- 128267 – Water Depth
- Full AIS PGNs (129038, 129039, 129040, 129793, 129802)
Garmin recognizes Cortex as a valid GNSS source and displays position, satellites, and accuracy correctly.
Victron Manual Requirements (GX Manual – Section 6.3)
The GX manual states that a NMEA 2000 GPS must meet:
- Device Class = 60 (Navigation)
- Device Function = 145 (Ownship Position / GNSS)
- Must transmit PGN 129025
- Optional: PGN 129029, PGN 129026
The Cortex broadcasts all required PGNs, but identifies itself as an AIS / Communications device, not Device Class 60 / Function 145.
Problem
Even though Cortex broadcasts valid GNSS PGNs, the Cerbo GX does not classify Cortex as a GPS source because its Device Class and Device Function do not match Victron’s required values.
As a result:
- Cerbo GX ignores Cortex GNSS PGNs
- GPS menu does not appear
- VRM tracking does not activate
- No position is shown in Cerbo GX
- Garmin (and other NMEA 2000 devices) work correctly with Cortex GNSS
Request
Can Victron:
1. Confirm whether Cerbo GX currently rejects GNSS PGNs from AIS‑class devices, even when PGN 129025 and 129029 are present?
2. Provide a firmware update or configuration option allowing Cerbo GX to accept GNSS PGNs from devices that do not identify as Device Class 60 / Function 145, but still broadcast valid GNSS PGNs?
3. Alternatively, can Victron add Cortex (Manufacturer ID 504, Model “CORTEX”) to the list of accepted GNSS sources?
Reason for Request
Cortex is a modern AIS/VHF system with a high‑quality GNSS receiver. Many boats use Cortex as their primary GPS source. Allowing Cerbo GX to accept GNSS from Cortex would enable:
- VRM remote tracking
- Trip logging
- Speed/heading display
- Position‑based alarms
- Integration with existing NMEA 2000 networks
All without requiring an additional dedicated GPS antenna.
Thank you for your assistance.
I can provide NMEA 2000 PGN logs, screenshots, or device instance data if needed.
Best regards,
Jose