* Potential engine fires in 106,800 Grand Cherokees
* NHTSA also explores rear differential failures in Dodge Ram
* 230,000 Ram pickups under investigation
July 23 (Reuters) - U.S. safety regulators have opened defect investigations into Chrysler Group LLC's 2012 Jeep Grand Cherokee and 2009-2010 Dodge Ram 1500 -- the automaker's two best-selling vehicles in the United States.
The National Highway Traffic Safety Administration said it is investigating potential power steering hose failures that could lead to under-hood fires in about 106,800 2012 Grand Cherokees.
NHTSA also is investigating potential rear differential failures that could lead to rear wheel lock-up and loss of vehicle control in about 230,000 2009-2010 Dodge Ram 1500 pickups.
An NHTSA defect investigation is often a prelude to a vehicle safety recall.
Chrysler spokesman Eric Mayne said, "Chrysler Group takes seriously all customer complaints and is cooperating fully with NHTSA." Mayne said owners of the affected vehicles who have concerns can contact dealers directly.
Chrysler is majority-owned by Italy's Fiat SpA. The Grand Cherokee was the first Chrysler model to be redesigned and released under Fiat's management after the U.S. automaker's 2009 bankruptcy.
NHTSA's Office of Defect Investigation said the power steering hose on the 2012 Grand Cherokee could fail, resulting in power steering fluid leakage in the engine compartment. It said the fluid "may be ignited by hot surfaces in the engine compartment."
NHTSA said it has received one complaint of a power steering return hose failure in a 2012 Grand Cherokee and has identified additional incidents of power steering hose failure in field reports submitted by Chrysler.
The office also said it has received two reports of alleged engine compartment fires in the past month, including one that reported "fluid dripping beneath the vehicle during the incident." NHTSA said the reports "allege severe fires resulting in total vehicle loss with the cause as yet undetermined."
In the Dodge Ram investigation, NHTSA said it had received 12 complaints of alleged rear differential failures resulting in rear wheel lock-up, including "one resulting in a crash into a concrete barrier."
NHTSA said one of the Dodge Ram complaints alleged drive shaft failure in which "the detached shaft end punctured the fuel tank."