I drove my 2013 Gen1 volt to work yesterday and got the Service High Voltage Charging System message when started the car to go back home where I am unable to charge the car again. My battery coolant level has not changed from the level recommended (well above the seam of the tank). I installed the WOT defeat plug on my Volt a couple of years ago to prevent the faulty low coolant sensor from causing the message to appear requiring an ECU reflash at the dealer which will not be covered under warranty or free, only to have the problem reappear when the faulty sensor fails again. I disconnected the 12V battery and checked the defeat plug which is just a resistor to fool the ECU the tank is full. It read 25K ohms across it which is probably correct. From all the post I can find on the subject it looks like the coolant sensor failure (or low coolant level) is the only failure I can find that will set the fault codes and this message. I just ordered a VCXNano GDS2 adapter to see the fault codes, clear and see if they immediately come back. Then trouble shoot from there. I am a former automotive mechanic and now an electronics technician so I feel comfortable doing this, but I really didn't want to have to become a master volt technician to own this car. I figure instead of giving my chevy dealer my money, I would spend the $140 bucks on the Nano and GM software and at least be armed with information if I need to take it in. Has any one seen the message after installing the WOT defeat plug?