For the second time this year, General Motors will halt production of the Chevrolet Volt for several weeks — but company sources insist the move does not signal problems with the plug-in hybrid which got off to a slow start after its introduction in December 2010. In fact, GM expects to report that demand has surged to a record for the Volt this month, more than doubling year ago levels. Depending on what happens the rest of this week, August sales could near 2,500, TheDetroitBureau.com has learned.