The cars are now on U.S. dealer lots and the repairs should be done by early next week, said GM spokesman Alan Adler on Friday. The fix takes about 30 minutes.

Eight models are affected, including the 2013 Cadillac XTS sedan and the newly launched 2013 ATS sports sedan, which just started to arrive in showrooms.

OnStar is an in-vehicle service best known for connecting drivers to live operators who can provide directions or summon emergency help after an accident. If a car is hit, OnStar's crash response system is supposed to automatically contact an operator, who then calls the vehicle.

But GM found in tests that a software glitch prevented the affected models from sending these alerts after crashes that do not cause the airbag to deploy, such as rear-end collisions.

The problem does not occur in more severe crashes that trigger the airbags, Adler said. The issue also does not affect the airbags themselves.

"In certain crashes, they should get a call that they're not getting," Adler said. He added that the issue was neither a safety issue nor a recall.

"That is a GM standard," Adler said, of the automatic crash response system. "We tell people to expect this."

Also affected are the 2013 versions of the Chevrolet Cruze, Equinox, Volt plug-in hybrid as well as the Buick Verano sedan and GMC Terrain crossover. Sales of the 2012 Cadillac SRX have also been halted.

(Reporting by Deepa Seetharaman; Editing by Gary Hill)

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