I just drove my Volt 3,000 miles. Mostly on gas. About 40 miles from home the check engine light came on. The message displayed, Service High Voltage Charging System. The car will not charge now. (on level 1 or level 2) I have asked onstar for the codes. (P1E00 and P1FFE) I have tried to research the codes. From what I have found it could be 3 things, the coolant may be low, the coolant sensor may be bad, the coolant pump may be bad. I have an appointment at the dealer today. I want to know as much as possible, before I go to the dealer. So, any ideas? How do you check the coolant? Thanks.