DETROIT—GM will halt production at its Detroit Hamtramck assembly plant, where it builds the Chevrolet Volt, for four weeks for retooling starting in mid-September.

DETROIT—Sales of GM’s Chevrolet Volt are picking up, leading the automaker to restart production a week early this month at its Detroit-Hamtramck assembly plant.

DETROIT—GM has restarted production of the low-emission Chevrolet Volt electric car. The company had briefly stopped production to add an emissions system fan and make some software changes.