G3X not reading 912iS ECU

Ken:

1. Review cabling is well done according to the Rotax Fadec Gea 24 schematic on the Garmin G3X install manual.

2. Do not connect the shield of the cable that ends on the GEA 24 to the shield of ECU A/B ground. Mantain 2 shields separated.

Ken,

Are you using the GEA-24 or the GEA-24B engine interface module?

Gea 24

Ken,

I assume you wired it like in the attached diagram.  As Maximio suggests, review your wiring for proper terminals and polarity.  The Lane A and Lane B CAN bus should be brought together within .3 meters (about 12”) from the GEA24, or right at the GEA24 terminals.  Most people ground one end of the shield, and that’s already done at the Rotax side, and it’s best to not to also ground it at the GEA 24, as to maintain isolation between the engine and airframe grounds.  It’s OK if the shield grounds for both lanes are brought together, just avoid tying them to the airframe.  You only need one end grounded for the shield to drain. 

There is a 120 ohm resistor inside the Rotax ECU at each CAN termination. This creates a 120 ohm resistance between CAN Lo and CAN Hi. Once you connect the A and B CAN buses together both resistors are connected in parallel providing the required 60 Ohm resistance across the two conductors. So the first thing I would do is go to connector P244 at the GEA 24 and check resistance across terminals 33 and 17.  If properly wired, you should see about 60 ohms.  And not meaning to be insulting, but the lanes have to be on for the Rotax CAN to send information to the Garmin GEA24. This means switched on with start power also on so you see the lanes lights come on and then go out.  Then leave start power on even if you are not going to start the engine.  This keeps the lanes active and sending data to the GEA 24.

Thank you so much for your response.  You are talking way over my experience level.  I am building a Van's RV12is which has a Rotax 912iS engine.  The avionics package and wiring harnesses are put together by SteinAir Inc., making it pretty much a plug and play install.  I haven't been able to call them due to the weekend and holiday but will do so tomorrow.  Hopefully they will say it is just a configuration problem.