Does the lane light initially illuminate when the lane switch and start power are turned on? If not you have a lane problem as Maximo suggests. If Lane B is otherwise functioning properly, but no display data is being received by the Dynon then maybe you have a data (CAN) bus problem.
The Rotax 912iS ECU sends this information over a CAN (controller area network) bus. Each lane has two CAN buses, one display and one diagnostic. Each bus is two wires plus a shield/ground wire. A CAN bus must have a 120 ohm resistor (terminator) at each end, yielding a net resistance of 60 ohms between the CAN-Lo and CAN-Hi conductors. The Rotax ECU provides one of those two resistors built into the ECU for each bus.
Assuming your Dynon system is using the SV-EMS-221 engine monitor module, the display can bus wiring terminates there. However, this module only has one display CAN input, so the Lane A and Lane B display buses are tied together, either at the termination directly, or just before it, typically within 12”. See the attached diagram from the Dynon install manual. Rotax recommends two different inputs for redundancy, but it typically works fine the way Dynon does it.
What is important to know is that Dynon does not provide the second 120 ohm resistor at the termination. Since the display buses for lanes A and B are now tied together, both resistors that are built into the ECU are now connected together across the bus and will achieve the 60 ohm requirement across the bus conductors. But you can see that with display bus A and B looped together this way, if something happened to either one of the buses, both would be compromised. So it’s odd that you would have a single lane not reporting if the physical bus was compromised. That being said, the bus can still operate with one resistor missing, it will just have more errors.
The way the Dynon module connects to the system provides a diagnostic opportunity. You can go to connector D37 and test across terminals 36 and 37 with an ohm meter. You should get approximately 60 ohms. If you do, you are assured the wiring to the display CAN to both lanes is good. If you get approximately 120 ohms, then the wiring to one of the two lane CANs is compromised. And of course you would suspect the wiring to Lane B since Lane A is still receiving data.
After that you need help from Rotax because you would be looking at a problem with the ECU. It’s unlikely that there is a problem at the Dynon equipment because the data for both lanes comes over the same bus from the Engine module to the display, and that is still working. I would also be interested to see if the maintenance bus for lane B is working. Have you connected BUDS and checked that?
