Steinorgy

I tried to get my 2004 sti ecu reflashed today but couldn't it kept coming up with an error "error voltage out of range" it said 12.7v, I checked the voltage on my battery and it was 13v DC when the car was off and then when I started it it went to 14v as per normal (from what I understand) I also checked the voltage from the alternator and it was the same, I have never had any problems with the battery starting it or keeping charge etc.

I have since then tried taking the alternator plug of and check the voltage on that and it this same and then when I plugged it back and started the car it threw a check engine light up.

This is all still new to me so sorry if it doesn't make sense, has anyone else had this problem ? Or know how to fix it ?