New installation, Lane B issues

Jerry,

This sounds like a problem with the maintenance CAN bus. If both lanes lights come on, then go off, the lanes are both active.

A CAN bus typically operates with a resistance of 60 ohms between the CAN Lo and CAN Hi conductors. This is achieved with a 120 ohm resistor at each end of the bus across the conductors. This puts the two 120 ohm resistors in parallel, yielding 60 ohms between the conductors. In the case of the Rotax maintenance CAN, there is one 120 ohm resistor in the ECU for each bus, so 60 ohms is not achieved until you connect these two buses together with the Y-cable at the maintenance ports. The Y-cable ties the two buses together to function as one bus that communicates with both lanes.  

Knowing this resistance allows you to do a couple of tests. First, put an ohm meter across each bus separately (no Y-cable connected) and you should get 120 ohms nominal across the Lo and Hi conductors for each bus. Once the Y-cable is connected, you should get 60 ohms nominal between the pair.  

Also, I think you may be confusing the lane A/B ECU bus voltage with alternator bus voltage. I assume you are doing this test with the engine stopped, so ECU is powered by the battery via the start power switch. In this case, each lane bus voltage should be essentially the same. I believe you are not seeing lane B bus voltage because your Lane B maintenance CAN is not connecting.  

 Note that the display can bus works the same way in that the lane A and lane B buses typically connect together at the engine interface module, thus connecting the two resistors (lane A and lane B) in parallel.  There are engine interface modules that connect the lane A and lane B buses separately, in which case each bus gets a second 120 ohm terminator at the interface module.

May want to try putting your key  the ACC position.  IIRC some Rotax installs require this. Can't hurt to try it.

Thank very much Jeff, I will try what you mention as soon as I can. I’ll let you know the outcome.