Will driving home my voltage indicator went to zero, but car was running normal. Installed maintenance code reader and it did not show any problem. Turned car off and restarted ok and the voltage indicator worked. I opened a window and the indicator when to zero. Each time I start the car the voltage indicator works. Don't know what is causing this. It happened once before and I changed the battery. The car runs fine, so I think the alternator is working ok. What else should I look at for this intermittent problem?