DETROIT (Reuters) - General Motors Co's GM.N chief financial officer said on Thursday the automaker expects another "very strong year" in 2017 and reiterated the company's earnings forecast for the year.

The GM logo is seen at the General Motors Warren Transmission Operations Plant in Warren, Michigan October 26, 2015. REUTERS/Rebecca Cook

“Overall, we expect a more challenging environment across a number of dimensions” in 2017, due to rising interest rates and falling used-car prices, CFO Chuck Stevens told investors and analysts on a conference call.

But thanks to an improving economy and lower fuel prices, Stevens said GM believes “we’re going to be in a reasonably constructive industry environment.”

Stevens said the No. 1 U.S. automaker will reduce inventory levels, a concern for Wall Street, to around 90 days in June from 98 at the end of March, and to around 70 days by the end of 2017.

He said a combination of solid economic indicators and cost-cutting should help GM maintain profit margins of around 10 percent.

The CFO’s conference call came just days after disappointing U.S. new light vehicle sales figures for March showed an annualized sales rate of around 16.6 million units.

Those figures had added to concerns that after a six-year boom cycle that U.S. auto sales might be set for a decline.

Stevens said GM still expected U.S. new light-vehicle sales for the industry at around 17.5 million units, after a record 17.55 million in 2016.

GM believes March figures were skewed by a mild winter that meant sales were “more evenly distributed” across the first quarter as opposed to prior bitterly cold winters, Stevens said.

GM still expects full-year earnings per share of $6.00 to $6.50, he said.

Stevens said the company expected its used car prices to come down around 7 percent this year as many leased vehicles return to the market.

Investments in autonomous vehicle technology are adding around $150 million in costs per quarter at GM, the CFO said.

The call came more than a week after billionaire hedge fund manager David Einhorn publicized a plan to boost GM’s value based on creating two stock classes, one that pays a dividend and another that does not.

GM rejected the proposal and rating agencies say it would negatively affect the company’s credit rating. Einhorn has promised a proxy battle where he hopes to win board seats, but has not released any names.

In a regulatory filing on Monday, GM announced a slate of board nominees, all of whom currently serve on the board.

GM shares were up 24 cents at $34.24 after the call.