This seems like an odd problem...at least to me.
2008 Mazda 6; I4; 2.3; 5 spd OD

Put the car in drive and off you go; sometime later the gear indicator on the dash will go out (you can no longer see what gear you are in or even if you're in D, N, R, etc; all other dash indicators are normal), and the transmission will either stay in the current gear, or it will shift down. A slight wiggle on the gear **** sometimes corrects the problem, or I can move the shift lever over to the manual position and back and that fixes the problem.

Using an OBD II scanner and the FORScan software I observed the "transmission range" output. I can see the transmission move from P to R (on the O'scope tab I see a downward transition from "P") then when I put the transmission into D it works correctly (dash indicator says "D") for a few seconds but the the dash indicator goes out and the FORScan software shows "error" for that module and the O'scope goes flatline. I wiggle the gear shift a little bit and the dash indicator comes back on (showing "D") and now the O'scope has output again.

So....OK....I can replicate the problem and I can see it in the software.....now what? I'm researching a bit but what is a "transmission range" error? I have (some of) the tools but not the knowledge.

Thank you

--Maxnpj

 

What fault codes are you getting?

 

This sounds to me like a bad neutral safety switch. I was recently having the problem on my 2012 Mazda6 with automatic transmission and 94K miles that the "D" would randomly blink off or even stay off for several seconds, while the tach would spike higher briefly because the tranny was in neutral rather than drive for brief period of time (momentary or a few seconds). Replacing the neutral safety switch completely solved the problem for me. The "D" is now rock solid and the tranny and tach are behaving normally as they should.

 

benhemp welcome to the forum..

Nice information to the possible problem.

Still should check for any codes.