Expanding its safety probe into Ford Motor Co.'s vehicles, the US National Highway Traffic Safety Administration (NHTSA) has recently revealed that it has initiated an investigation into complaints pertaining to the engine stalling and surging issues on some of the Ford vehicles of model years 2009 through 2011.

Revealing that it has received 1,448 complaints involving the alleged engine issue, the NHTSA said that the investigation will affect nearly 724,982 Ford vehicles, including Escape compact SUVs and Fusion sedans, as well as Mercury Mariner SUVs and Milan sedans.

The expansion of the safety probe by the NHTSA is apparently an outcome of the fact that the safety regulator received a broader set of complaints in October 2012; when the agency had said that the alleged engine problems could affect nearly 1.6 million Ford vehicles. 

According to the NHTSA, the initial complaints were largely focused on the Escape SUV models from model year 2005 to model year 2012. The initial inquiry carried out by the agency revealed that some other Ford vehicles - manufactured during the period from between June 22 to October 15, 2009 - apparently had contaminated printed circuit boards "plating variations" which could potentially result in a lack of continuity in the throttle position sensor circuit.

Noting that the engine issue may cause the drivers to experience varying levels of reduced engine performance through three so-called "limp home" modes, the NHTSA said the partial loss of power may often get characterized an engine stall by the drivers.