I was leaving for work and a few blocks from home.

Suddenly, the main indicator screen in my volt went black. It still ran fine, and I had to get to work, so I continued to work without speed indication.

I called the volt help line and the lady told me there was one other report of this problem, but they had not solution.

When I was done with work, I started my car and it all worked. I'm guessing some sort of software "glitch" which just required a re-boot.