The US National Highway Traffic Safety Administration (NHTSA) has recently revealed that the Hyundai Elantra "severed ear" air bag investigation has been expanded, to include two 2011 and 2013 Elantra models; with model year 2012 Elantras already being examined for the problem in a May-launched probe.

In addition to the expansion of the investigation to include the 2011 and 2013 Hyundai Elantra models, the NHTSA has also revealed that it has upgraded the probe to an engineering analysis, which brings the proceedings one step closer to a recall of the under-scrutiny models.

Though the initial investigation by the NHTSA involved 123,000 Elantra 2012 models in May, the US safety regulators said in a Monday disclosure that the air bag issue affects only the Elantras manufactured in Korea; with 75,000 of the affected vehicles having been sold in the US.

The NHTSA initial investigation into the reported air bag issue in 2012 Elantra models began after a complaint which highlighted the problem by pointing out that the deployment of the air bags, in a crash, severed the driver's ear in half.

While the complainant noted that the side air-bag deployment in the affected Elantras released a piece of loose metal which cut the driver's ear, Hyundai has apparently tried to downplay the severity of the complaint by terming it as an isolated incident; saying in a May statement that there have been "no other reports of injury from side curtain air bag deployment in 2012 Elantras.