The National Highway Traffic Safety Administration notified Chrysler Group LLC that it has begun a preliminary investigation into more than 100,000 2012 Jeep Grand Cherokees and 230,000 Ram 1500 pickups model year 2009 and 2010.

NHTSA notified Chrysler last week that it was beginning the investigation into the Grand Cherokees after receiving two complaints that the engines caught fire. According to one complaint, the driver noticed power steering fluid leaking onto the ground shortly before the engine caught fire. Jeep agreed to replace the vehicle for the owner. No one was reportedly hurt.

"Both complaints were received within the last month and allege severe fires resulting in total vehicle loss with the cause as yet undetermined," one NHTSA report read.

The Ram 1500 investigation involves a dozen complaints about problems with the rear differential failing and causing the rear wheels to lock up. Out of the 12 complaints, one involved an accident, though no injuries were reported.

Chrysler was notified of the investigation on July 19.

"Chrysler Group takes seriously every customer complaint and is cooperating fully with NHTSA's investigation," said Chrysler spokesman Eric Mayne.

A preliminary investigation is opened to see if there are more vehicles with similar problems. Ultimately, it could lead to a recall, but nothing has been determined yet.

The Ram and Grand Cherokee are the two best selling vehicles for Chrysler, which has seen sales climb 28.6 percent this year.

Meanwhile a much bigger potential problem looms over Chrysler as NHTSA investigates more than 5 million Jeep Cherokees, Liberties and Grand Cherokees, going as far back as 1993 model year. NHTSA is attempting to determine whether the gas tank is dangerously placed behind the rear axle resulting in fires after rear end collisions.

That investigation began in 2010.