The one annoyance when driving the Volt at night is if the center rear view mirror does not dim properly. Mine has operated about 10% of the time, but when the dome light shines on the mirror's sensor, it is operational and dims.
After several weeks of frustration, I got the idea to turn the mirror upside down. This is done by moving it to a slight angle so you can turn it 180 degrees and then return it to the normal angle. Since there is an electrical wire inside, be sure to remember the direction you turn it so you can reverse the turn and avoid stressing the wire if returning it to the original position.
Instead of the sensor at the top, it now is at the bottom. The angled sides of the mirror match the rear window better too. An amazing difference, now the mirror dims almost 100% of the time. Mine may have been manufactured with the sensor slightly off center in a vertical direction, so the light from the cars behind me is not hitting the sensor just right. I do plan on asking for a replacement, but I thought it best to mention the problem on the forum so others would know a possible temporary "fix" if their mirror had a similar problem.
One other improvement may occur with the mirror upside down. The front sensor moves from the drivers side to the passenger side. The black box just to the right side of the mirror helps shield the front sensor from headlights or other night lighting that may decrease the dimming action.