General Motors is returning to Facebook.

The automaker pulled its ads from the social media giant last May, just days before Facebook's initial public offering. GM said the ads on Facebook weren't effective and didn't justify the $10 million per year it was spending.

But on Tuesday, Chevrolet's U.S. marketing chief Chris Perry said GM is introducing mobile-only Facebook ads for the Chevrolet Sonic subcompact car.

Perry didn't reveal any details about the ads or say how much GM is spending. But he said GM is using new methods to target the ads and measure their effectiveness.

Facebook recently boosted its ability to track the impact of ads with the purchase of Atlas, a set of online marketing tools.

Microsoft sold Atlas to Facebook at the end of February.