DETROIT (AP) — General Motors will strengthen the structure around the batteries in its Volt electric cars to keep them safe during crashes, a person briefed on the matter said Thursday.

GM will ask Volt owners to return the cars to dealers for structural modifications, said the person, who did not want to be identified because GM executives plan to announce the repairs later Thursday.

The fixes are similar to a recall and involve about 8,000 Volts sold in the U.S. in the past two years. GM is making the repairs after three Volt batteries caught fire following crash tests done by federal safety regulators. The fires occurred seven days to three weeks after tests and have been blamed on a coolant leak that caused an electrical short.

GM's move is considered a step below a recall, which would be issued by a car company and the National Highway Traffic Safety Administration.

NHTSA and GM have said the electric cars are safe and that no fires have occurred after crashes on real-world roadways.

The Volt has a T-shaped, 400-pound (181-kilogram) battery pack that can power the car for about 35 miles (56 kilometers). After that, a small gasoline generator kicks in to run the electric motor.

NHTSA has been investigating the batteries after a Volt caught fire in June at a crash test facility in Wisconsin. The fire broke out three weeks after a side-impact crash test.

GM said the Volt's battery should have been drained after the crash, but it never told NHTSA to do that. Later, two GM executives said the company had no formal procedure to drain the batteries until after the June fire. GM has said that the liquid solution used to cool the Volt's battery leaked and crystallized, causing an electrical short that touched off the fire.

The company now sends out a team to drain the batteries after being notified of a crash by GM's OnStar safety system.

The company sold 7,671 Volts last year, falling short of its goal of 10,000. It was outsold last year by its main electric car competitor, the Nissan Leaf, at 9,674.