Aux Battery Voltage on CarScanner

It could be either or neither, depending on which sensor the diagnostic software is polling. IMHO; it's better to use your own test equipment to troubleshoot something; because you don't know if it's a sensor problem, a battery problem, or a wiring issue. Not having your own, known good, DVM, you won't be able to isolate the issue. This would send you down a rabbit hole of a parts cannon. A DVM at harbor freight is less than $10.

 

Pin 16 of the diagnostic connector is always powered, and AFAIK most OBD tools that show you 12-volt system voltage are just making their own measurement of that voltage and telling you.

Now, several ECUs in the car also measure the voltages they're seeing, and when you pull up live-data screens for those ECUs you'll see those measurements.

 

That is what I have displayed on the infotainment screen via CarPlay and OBD Fusion on my '26.
I found that Car Scanner consumes a lot of phone battery-I couldn't get around it.
14.3 volts in the winter, and now I'm seeing 12.7, when running.

 

That's NOT the battery voltage; that's the DC-DC converter system output voltage. That's why I tell people to use their own test equipment, so they don't draw the wrong conclusions.

A BM2 battery monitor will tell you your actual battery voltage at rest.

 

Your own equipment, if you read it when the DC/DC converter is operating, will also show you the DC/DC converter output voltage.

 

Your correct; My assumption was that they're smart enough to not turn-ON the car before taking a direct battery measurement.
Sorry; I assumed that was a common sense thing......

And your probably just "busting my chops"...

 

Not interested in busting anybody's chops, just pointing out it's the timing of the reading that determines whether you're seeing battery voltage or converter output voltage, whoever's equipment is involved.

Because pin 16 at the diagnostic connector is always powered, it's always there for an OBD tool to measure, even when the car is off and the tool can't scan any ECUs. A reading you see at that time will reflect the battery voltage.

(There might be some OBD tools or apps that would get stuck trying to connect to ECUs and not show you even their local measurement of that voltage; that would be an unfortunate design choice but I can't guarantee it's never been made by some tool or other.)

 

Sorry; I didn't mean to get into the "weeds" on this one. I stated way back in #3 to use a DVM for that measurement.

I believe pin 16 is on a fuse and the car scanner app is tethered by a Bluetooth OBD2; so if it doesn't shut off with the car - it'll eventually drain and kill the battery - if it's not a daily driver. Don't know if that app will give a resting 12V value or if that Bluetooth dongle stays powered ON after the car shuts down. That would require reading the Bluetooth dongle specifications.

 

My dongle goes to sleep. (That sounds a little weird, lol).

 

Feels weird when it happens, too.