Just so you know, that isn’t true.
That's usually true for other cars I have worked on but it seems your right the Volt may be different.
I think both issues below are related to the weeks and weeks of hot weather we are having where I live. My car is high mileage now so anything out of the ordinary could cause problems. Quick update and some info:
1. The "Service High Voltage Charging System" was triggered by low coolant. There may be a coolant leak. Dealership will have to find out. Only way to get rid of it is to take to dealership and have computer reset for $110 (there is a tool for this that requires PC software for $130 on Amazon according to other threads). I don't know if my extended warranty would cover the leak repair so if it doesn't I will just have to keep filling it with coolant until I sell/trade it. Winter/Fall temperatures need to hurry up and get here. This hot weather is making that system run a lot on my high mileage Volt.
2. The Volt is no longer reporting the P code for the Intake Air Temperature Sensor. The wires to the MAF plug look fine (I've seen worse) but my cars engine bay is super dusty which could be causing air intake issues although the air filter is clean. Most of the time the P code (check engine light) doesnt come on unless its over 90 degrees outside. That makes me think the MAF is dusty and needs to be cleaned out using throttle cleaner. It's strange how a tripped code would simply vanish after a while??? That doesn't happen on a normal car usually. I also don't understand why they wouldn't have a MAF code trip if its actually part of the unit. That's why I was searching so hard for the "air intake temp sensor".