Fuel level sending unit.

[Karl]

If you do remove the tanks for any reason then inspect the lower surface of the tank around the small bumps that look like dome head rivets, they are actually welds but the tank often cracks in this area.

Not an official repair but I have seen many cracks in this area that were sealed over with epoxy, seems to work well at least for the jet A1 operators.

[NAH7853]

Update on progress
Wings were removed and tank hoses were replaced. Senders all checked out.
When all was reassembled got a Red X on the LH tank again. Mechanic made a wiring harness extender and when we plugged the LH aux tank sender into the RH harness it worked fine and when we plugged the RH aux tank sender into the LH harness it also works fine.
Called Diamond and they had no clue but when all else fails “ reload the G1000 software”. An expensive experiment but no clue what the next step should be.
Hope it works

[Lance Murray]

I have had a bad connection at the molex connector near the probe. Check the connection before removing the probe.

[Lance Murray]

I would use Proseal not epoxy.

If you do remove the tanks for any reason then inspect the lower surface of the tank around the small bumps that look like dome head rivets, they are actually welds but the tank often cracks in this area.

Not an official repair but I have seen many cracks in this area that were sealed over with epoxy, seems to work well at least for the jet A1 operators.

[rwtucker]

One other possibility -- a long shot -- is software. I have had Garmin shops misload tank configurations with similar results. Have you had a software update reently?

[NAH7853]

During my November annual the shop did install a GTX345 which I assume required a software update. It didn’t show up right away because I always fly with full tanks but I think it started the first time the aux tank was empty after the ADS-B upgrade. Could this be the cause?

[Lance Murray]

Have them reload the software. When loading software the user has to choose all the correct options for your plane. Possibly they didn't choose the correct option for your fuel tanks.

[pietromarx]

I did the tank calibration myself (in the mechanic's hanger with him participating) after replacing the sender the other week. It was interesting, fast, and very useful. If you are comfortable with somewhat technical digital issues then you should park the airplane in a level hanger (preferably your mechanic's), drain the tank, and then recalibrate it using the Garmin maintenance procedure. Do it methodically and everything will be fine. (It is much faster and easier than the equivalent for Cessnas and other G1000 installations.)

[NAH7853]

Problem Update. They did the software update and recalibrated the fuel gauges. It all worked fine until the next time the LH aux tank went empty and then another RED X. After several hours on the phone with Garmin it was determined that the GEA71 LRU was the problem. They replaced the LRU and reloaded the software and all seemed to work fine yesterday at the shop with no RED X and the LH aux tank empty. Then when they rebooted it this morning to double check before I picked it up the RED X was back. I would love to hear if anyone has any other thoughts on this? Pretty frustrating.

[ThomasD]

I expect that you have already done so, (and don't want to state the obvious) but if not get your mechanic to do a really thorough wiring check, including pulling on every crimp and wire individually and visually inspecting inside the connectors (with a loupe) and buzz out impedance