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Reporting a failure of a GTX345R transponder on my DA42-VI after 2 years and just under 200 hours. The unit initially failed ('XPDR Fail' with the yellow 'X') 3 hours after the annual . Thankfully a simple reset of the circuit breaker resolved the issue THAT TIME. On a subsequent flight the transponder failed again just as I was entering the mode-c veil around Boston. This time resetting the circuit breaker, avionics, and master switch did not remedy the failure. Re-seating the unit in the mounting bay also did not resolve the issue. The unit is off to Garmin for repair but I wanted to share with this community in case anyone else has experienced the same issue.

My 345R had a really hard time when it got hot. We chased the issue a bit and then at the last annual, in Ft. Worth, the heat was bad enough that the problem showed up on the test flights. So the (brilliant) mechanic built custom cooling ducting to keep the innards of the transponder cooler and now it has been fine.

Thanks for the advice. I will keep it in mind.

The transponder ending-up having a board failure... $1,400 repair from Garmin and its good as new.