12V error

It is possible to have a battery that reads 12.3v but then falls quickly when trying to Ready the car.

You need a load test on that 12v battery. If it fails you need a new battery.

Most auto supplies can do it but you may want to move the covers out of the hatch area first.

 

You don't need to on a gen4

 

If you continue to get that second error message; your brake pedal switch may be intermittent. That may become dangerous; since that also drives your brake lights.
I've developed the habit of hitting my hazard lamps when I hit slow moving traffic on the interstate - don't want someone coming around a blind curve thinking I'm going full speed - when traffic is only creeping. I know I've avoided a few collisions; because I've seen several cars lock-up their brakes in my rear view mirror.

 

Newer cars are very sensitive to voltage variations; because of their computer controls. That said; the first thing to do is to FULLY test the starting battery. Low voltage/amperage can cause all kinds of phantom errors to crop up; so take care of that FIRST - clear all error codes, then see if anything pops back up. A defective part will error again; a phantom error due to low voltage/amperage won't.

Hope this helps.....

 

The conditions that an ECU has to see to trigger a particular trouble code can be quite finicky, and usually have to crop up on two consecutive drives to trigger the code.

Because of that, the plan of "clear it, then see if it comes up again" is often not as definitive as it sounds; if the code was reporting a real issue, you probably will see it again, but that may happen weeks or months later.