The National Highway Traffic Safety Administration (NHTSA) is pushing its investigation one step further in almost 1.2 million Toyota Corolla’s and Matrix cars’ probable troubles in stalling.

The concern is that the engine can stall at any place in any time without advance warning and it will not restart, according to the description of NHTSA.

Last November, the authorities had started its preliminary investigation wit regards to the problem. At that time, the analysis riveted only the 2006 model of Toyota Corolla and Matrix Cars, which is the wagon version of the Corolla. However, at present, the concern has now been upgraded to an engineering investigation; a more specified and detailed type of analysis.

This time, the investigation involves model ear 2005 up to 2007. Collectively, Toyota and NHTSA have gathered as many as 1,100 protests of stalling engine, which includes six cases that engaged fires or crashes, according on documents presented by NHTSA.

By the time the preliminary investigation was started by NHTSA, Toyota had discovered two likely causes in engine troubles, in accordance to the NHTSA documents. Both cases include manufacturing troubles with the electronic control units of the car’s engine.

Moreover, Toyota said in a letter to NHTSA dated March 2, 2010 that based on its investigation; Toyota said that they do not consider the alleged defect makes a difficult risk to the security of motor vehicle.

Toyota said in the letter that they believe that when there are any troubles on the electronic control unit, it is anticipated that the engine will stall, which allows the engine to run, endangering a probable catastrophic collapse or fire.

The letter however was written to answer NHTSA’s request for information. It also provides elements of some steps Toyota had already done to attend to the problems in its engine that is related to electronic engine control units on the Toyota models involved.