General Motors Returns, Tentatively, to Facebook

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When General Motors pulled its advertising dollars from Facebook just days ahead of the social network's IPO in May 2012, it dealt Facebook a massive blow. Although it only pulled about $10 million in paid ads, GM's move raised major questions about the efficacy of Facebook's ad products. Now, 11 months later, the automaker is returning to Facebook.

Starting Monday, GM is running what it calls a "test program" on Facebook for the Chevrolet Sonic, which will be entirely focused on mobile ads..

(Read More: Why It Might Be Time to Jump Into Facebook)

GM's return comes after Facebook has made a major push—and serious investment—to demonstrate the impact of its ads. It's working with a series of third parties, including Datalogix, to track users' in-store purchases after they see ads.

The new ad options and measurement seem to have worked.

(Read More: Facebook Wants to Be Your Smartphone's Home Screen)

GM's vice president of U.S. Chevrolet marketing, Chris Perry, said in a statement, "Today, Chevrolet is launching an industry-first 'mobile-only' pilot campaign for the Chevrolet Sonic that utilizes newly available targeting and measurement capabilities on Facebook."

Facebook issued a statement saying: "We've had an ongoing dialogue with GM over the last twelve months and are pleased to have them back as an advertiser on Facebook. We look forward to working even more closely with GM in the coming weeks and months."

(Read More: Facebook Feels Hot Breath of New Apps on Its Neck)

—By CNBC's Julia Boorstin; Follow her on Twitter: @JBoorstin