T/M System Error, Dealership says Battery is Healthy, Replace Anyway?

[azpitts007]

Hi, I have a 2015 Nissan Leaf SV. I've had it for about 3 months, with no problems. Last week the car had a T/M System Malfunction Error and took it to the Nissan dealership. Tested the big and 12v battery and both came back healthy (12.6V). Took the car back and got the code right away.

For those who have gotten the T/M System Malfunction Error, but 12V battery tested okay, what was the next step? Also, could the AC be at fault? I noticed that when I turned the AC off first, no T/M code. But when I left the AC running when I turned the car off, I got the T/M error.

 

[azpitts007]

 

[azpitts007]

Update: Dealership called back and wants the car in for 3 hours of diagnostic to check for a short in the master wiring harness. Thoughts?

 

[azpitts007]

Update: Instead of messing around with a potentially super expensive fix, should I replace the battery? The dealership tested it and said it's okay but this T/M error seems like it's almost always the battery at fault.