With the same connection I can read depth sounder info from the bus so the connection could be ok. Also that two channel test shows the connection should be ok. Could it be that GNX 20 is "refusing" to communicate with non genuine NMEA 2000 device? Would it be interesting to know if the other arduino with actisense listener sketch is reading what the other with temperature monitor is sending? Would two arduinos one sending and one recieving see each other as devices on the bus?