Negative aux battery voltage?

More than likely a "glitch" but in Torque Pro though.

 

Why would you even pay attention to something so silly actually. Minus 25 volts It's a 12 volt system you know automatically that something's not making any sense and it's probably some kind of computer error or screwed up BS in something called an app which just naming something an app to me in other word for fubar. Use a real device like an electrical tester which obviously you did. To ascertain the real readings of your battery batteries or anything else you're working on your car maybe an app you know is made for I don't know something else real tools are made to get real things done there's no way your battery your auxiliary battery or your 12 volt as we call it is going to have negative 25 volts logically that really doesn't compute even negative 12 volts doesn't even make sense unless you connected your leads wrong on your tester You have seen that right where you get a minus sign in front of your voltage because you've put the red on the black and black on the red on the tester reverse the leads in other words yeah but that's interesting stuff I guess that's why I don't use too many apps they use real tools made by real companies that have serviced things for generations not phones with apps.

 

As I understand it, when an OBD-II device is reporting the 12-volt voltage, that is not some PID that it queries an ECU for; there's simply an A/D converter built into the dongle that measures the voltage of pin 16 (which is always connected to a powered 12 volt circuit) and the app shows you that measurement.

We can be sure the overall 12 volt system did not go −25 at that moment, as no fuses blew and no magic smoke escaped. A person with geek-level curiosity might want to know just where the glitch was: could the dongle's ground-pin connection have been bad for a moment, and appeared to be above pin 16? Or is the A/D converter flaky in that dongle? Or did the app read/display it incorrectly?

But that would be pretty hard to sort out, unless it starts recurring enough to investigate, and unless anyone was really that curious.

 

Clearly a glitch, but maybe in the communication protocol rather than in the hardware? The various ECUs all have to talk on the same lines and the packets might have collisions once in a while, resulting in bogus data. Or some ECU may receive a high priority interrupt during a measurement or the transmission of a measurement, resulting in the sort of garbage reading which was observed.

It could even have been a stray cosmic ray, as these are known to flip bits when they hit semiconductor electronics. That isn't a hardware failure per se, more of a signal to noise issue.

 

Again, an OBD-II reader's usual reading for the 12-volt voltage doesn't come from any query of the car's ECUs; it is a direct measurement of the voltage on pin 16 of the OBD-II port, made by circuitry in the dongle itself. So there aren't so many places for the glitch to be. If it was a communication protocol glitch, it would be in the communication between Torque Pro and its dongle, which only has those two participants.

(Some of the car's ECUs do have PIDs that report the 12-volt voltage, so it would be possible to have Torque or another scan tool configured to display one of those, instead of the dongle-measured reading, but if the OP was doing that we wouldn't know without the OP saying so.)