I've been monitoring some engine parameters using a real time OBDII scanner and one of the things I'm monitoring is the control module voltage. Curiously, the voltage varies between 13.9V and 12.3V. For example, I was sitting at a red light and it was 12.3V, then I turned on the headlights and it increased to 13.9V, then dropped again while driving. So bizarre.

 

This is normal per my understand of our electrical system. Our system is designed with a two stage voltage regulator (two voltage values). It determines which voltage is needed for best performance and best efficiency. One scenario is when the battery is fully charged a lower voltage output is satisfactory. I try to find the document that explains this.

 

Scroll down to BATTERY MANAGEMENT SYSTEM (BMS)
2012 Acura TL - Powertrain - Honda.com

 

Thanks for that. Glad to hear it's normal.