2016 TACOMA ECU reading low volts

Just purchased my 2016 limited v6 4x4. Took it to the tuner yesterday to upload the kdmax tune. My ECU is saying battery voltage is 4 volts.
-Tested battery and its reading properly
-Checked obd fuse and it was good, but replaced anyway
-Checked obd pin 16 to pins 4 & 5 and it is reading over 12 volts like it should

Tuner cannot upload the tune with a 4 volt battery reading.

Has anyone else had this problem and found a solution, before I take this to the dealership to diagnose?

Note: Truck runs great, no issues. Just wanting to get it tuned without problems.

 

Welcome to the forum

If the truck runs great with no issues there might be a problem with the tuners equipment -- or perhaps fate is giving you a hint to leave well enough alone...

 

This.

This is very very likely a DLC issue with the tuners equipment. We see this with dealer scanners when the scan tool has a damaged or worn connection, and it prohibits us from updating firmware.

If the ECU was reading 4V you'd have other issues and many codes like to trigger with this. As the ECU has to supply a constant 5V which would be impossible without a clean 12v source.