DETROIT (AP) — U.S. safety officials have ended a probe into allegations that three Ford SUVs can roll away even when they have been shifted into park.

The National Highway Traffic Safety Administration said in documents on its website that the investigation involved about 1.5 million Ford Explorer, Mercury Mountaineer and Lincoln Aviator SUVS from the 2002 to 2005 model years.

The agency determined that failure rates on transmission and brake parts weren't high enough to take further action, such as a recall. The probe began in April 2009 and was closed on Feb. 12, the agency said. NHTSA found 36 complaints including 14 crashes and six injuries.

Investigators found that the park gear in the transmission failed only 4.4 times per 100,000 vehicles. A system that prevents the car from being shifted into gear unless the driver's foot is on the brake failed only 3.4 times per 100,000 SUVs. NHTSA also said there have been few complaints about the issue in recent years, with the trend declining dramatically.