Reading Voltage With a Scangage II

What can I learn from the voltage reading on an OBD-II type scangage?

When the motor is on, I am reading 14.2V

I guess I could also read the state of a resting battery by turning ACC only.

What other failure modes or scenarios would I see a different voltage (other than 14.2V)

Nothing wrong with the vehicle, just curious what utility there is in reading the onboard voltage.

Thanks in advance...

 

I monitor voltage with an LED indicator light that changes color depending on voltage range, as well as an Ultragauge. To me, monitoring engine vitals is extremely important and a quick glance can tell me if anything is acting up before it gets worse.

If there is an electrical issue, alternator is going bad, or has gone bad, belt slippage/belt loss, battery won't hold a charge, etc. having onboard voltage gauge will let you know.

I've also added an LED oil pressure indicator that changes color depending on pressure since the PCM doesn't monitor that.

 

It's good for offroading, after blasting through water you can see if the alternator took damage.

It's also good when the alternator is weak and lights are dimming.

They are all but obsolete now, modern cars have battery load sensors along with more sensitive idiot lights. But I would certainly want it along side other critical numbers.

 

Computers & vehicle sensors may act up when voltage gets lower than 12 volts.
I've seen people chase an engine miss with a new tune up and not found the problem till they replaced the battery.