The National Highway Traffic Safety Administration said it will continue its investigation into cracks detected on the rear lower control arm of Nissan Motor Co. Ltd.'s model year 2013 to 2018 Nissan Altima despite the carmaker's initiative to fix the fault, according to a July 29 notice from the agency.

In January 2018, the Japanese carmaker implemented design changes to improve the durability of the lower control arm following reports that a crack may develop on the said component because of higher-than-usual stress and loading.

In addition, road salts that are used to treat ice and snow can cause corrosion and further worsen the crack. Nissan said road tests and field observations show that a separation is highly detectable and that the vehicle can be safely brought to a stop. The automaker said that low incident rate, ease of detection and low risk of adverse vehicle dynamics do not pose an unreasonable risk to road safety.

Nissan said it will replace the lower control arms of model year 2013 Altima in specific states with high salt usage. The corrective action is expected to be carried out in stages beginning late 2019, the NHTSA said.

The agency said it will nevertheless continue to collect analyze field data, as well as seek additional information and data regarding the potential safety consequences of rear lower control arm failure.

The defect affects about 2,043,354 units from model years 2013 to 2018. There are no known incidents or injuries connected to the defect, the agency added.