Small aux battery ok, but car won't start, no lights or sounds anywhere in the car.

14v means you have a bad auxiliary battery. a good one would read between 12.4 and 12.9

if you put a load on it, it will drop to nothing, which is what is hapening when you step on the brakes and press the power button.

replace it, and you'll be good to go

 

well hang on....

14v is plausible while the car is running (ready mode) and the battery is being charged, but that tells you little to nothing about the battery's health.

Turn on the ignition but don't go into ready mode. Turn on the headlights to create a load. Give it 4-5 minutes and then check the voltage.

 

how could the car be running, based on the o/p?

 

Thanks, I read it wrong and misunderstood the setup. But it's still fair to ask, "How can a battery that tops out at 12.8 volts read 14 volts unless something is charging it?"

Perhaps this OBD/app combo just isn't reading correctly?

 

yeah, definitely confusing.

 

This is easy: the included voltmeter is bad. Get a different voltmeter.

I had to address a similar problem recently when Sis and BIL needed to specify the voltage for in-floor heat in a bathroom remodel. They were getting a nonsensical reading from their voltmeter on the available circuit for the old baseboard system, so called me for advice. Walking them through some check measurements on other circuits, and some other evidence, we quickly figured out that it was reading 35% too high.

 

What is the:

“Happening all the time”?

So it’s been going dead for a while I guess. Time for a new 12 battery and whatever obd your using its impossible to show battery voltage at 14 unless it’s running. So there’s that....

A g2 Prius is the last car on the planet you want to jump start.

 

Fair enough. I can't say I can remember the last time I encountered a volt meter with enough of a fault to matter for the task at hand, but it certainly fits.

 

well, if the meter is bad, maybe the battery is fine

 

There is also the possibility that there are multiple issues.

Has the car ever been jumped?

Have the battery connections in the rear at the 12 V battery been checked for tightness and that they are free of corrosion? There are three places to check, the positive battery terminal (under the red cover) the negative battery terminal, and the bolt where the negative connects to the body of the car.

The lock/unlock (they aren't specific about whether there is SKS or not) does not say whether it is remote or keyless, but the language leans to the former.

That explains most things, but here's another thought, the car is on in READY, but the CM (combination meter) has died. The car must be in at least IG-ON, to get a reading on the OBDII.

If the car is in IG-on or READY, then the 14.0 V on the OBDII tells us the battery is being charged and is in the low-ish region. So nothing an external charge with a good automatic multi-stage AGM battery charger would not fix. Further diagnostics on the 12 V battery wouldn't be a bad idea also. But focus on the CM initially, which should throw a code BTW.

More info required from the OP.