The agency has received several complaints of apparent exhaust fumes entering the cabin. The issue was reportedly handled at first via a service bulletin, warning that 2011 to 2013 models can "exhibit an exhaust odor" when the climate-control system is active.
The company currently faces a lawsuit, however, filed on behalf of owners concerned that the exhaust smell is evidence that carbon monoxide or other toxic gasses are collecting in the cabin, according to Reuters.
The NHTSA is now "reviewing all available data" but has not yet decided if it will escalate its investigation or ask for a recall.
The company has reportedly acknowledged the concerns and has promised to take action if necessary, though it has not announced a formal recall.