Sales rose mostly because of discounts of almost $10,000, or 25 percent of the Volt’s sticker price, according to figures from TrueCar.com, an auto pricing website. Other pricing services gave similar numbers, and dealers confirmed that steeply discounted Volts are selling better than a few months ago.

GM’s discounts on the Volt are more than four times the industry’s per-vehicle average, according to TrueCar estimates. Edmunds.com and J.D. Power and Associates say they’re about three times the average. Discounts include low-interest financing, cash discounts to buyers, sales bonuses to dealers, and subsidized leases.