Yes, not a failed sensor...a transmitter failure.
I've been using the G4 for a few months and have been really happy with it (aside from the adhesive problems). This past week, though, I had three "out of range" episodes that were very unusual. All three episodes were the same. For an hour duration, I would get an "out of range" indication even though the receiver and sensor/transmitter were close to each other. After the third occurrence this week I called Dexcom and told them about it. I was concerned that my transmitter was heading to an early death. Tonight coming home from work it in fact happened...my receiver vibrated in my pocket and when I took it out I had a "Failed Transmitter" indication. That is an irreversible/unfixable message. I called Dex tonight and they are sending me a replacement.
Bad timing...6 am flight tomorrow for a business meeting, and I threw away all my old Seven Plus stuff so I am "naked" until I return home and get the new transmitter installed. I knew I should have kept the old stuff as a backup!
As an aside, Dexcom really needs to invest in more technical reps...no longer do you get someone on the phone right away. The wait is substantial. Yesterday (my third "out of range" incident) I didn't get a call back until the next day.