Federal regulators want to know why it took Hyundai and Kia 18 months to recall nearly 1.2 million vehicles that may have the same engine defect that resulted in an earlier recall of 470,000 sedans.

The National Highway Traffic Safety Administration has opened an investigation into Hyundai and Kia’s handling of the recalls affecting a total of 1.6 million vehicles that could experience engine failure while on the road.

According to the NHTSA investigation notices for Hyundai [PDF] and Kia [PDF], the agency is looking to address the timeliness and scope of the carmakers’ “Theta II” engine recalls, and their compliance with reporting such issues.

Hyundai first recalled 470,000 model year 2011 and 2012 Hyundai Sonata vehicles equipped with a 2.0 liter or 2.4 liter gasoline direct injection engine in Sept. 2015, determining that cars may contain metallic debris that was not fully removed during manufacturing of the engine crankshaft.

The carmaker said that if debris remains, oil flow may be restricted through the connecting rod bearings, causing connecting rod damage and possible engine failure.

At the time, the company said the recall was limited to vehicles produced on or prior to April 12, 2012, stating that a process change in April 2012 resolved the issue of manufacturing debris.

Despite this, Hyundai and Kia revised the recall in April 2017 adding nearly 1.2 million additional vehicles.

In all the recall now covers:
• 2011-2014 Hyundai Sonata
• 2013-2014 Santa Fe Sport
• 2011-2014 Kia Optima
• 2012-2014 Kia Sorento
• 2011-2013 Sportage

According to a chronology [PDF] submitted along with the March 2017 recall, the carmakers note that they began investigating the issue after Hyundai’s initial recall.

Kia said that after learning of Hyundai’s initial recall it checked its Theta engine manufacturing process for the Optima, determining there were different procedures and no issues. After finding that warranty and field claims were “extremely low” the decision was made to take no action.

However, in early 2016, Kia learned of recently returned engines and of Hyundai’s warranty extension program for the Sonata. In May 2016, the carmaker analyzed field data finding a slight increase in warranty claims, leaving it to extend warranty programs.

Two months later, the company found an increase in Theta engine claims for some vehicles, once again leading it to expanded warranty programs.

Between Dec. 2016 and March 2017, the carmaker continued analyzing data related to the vehicles, noticing a slight increase in warranty claims. It then eventually determined a recall was necessary.

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