The National Highway Traffic Safety Administration is investigating about 2,108 units of Mitsubishi i-MiEV compact electric vehicles following reports of loss of power-assisted braking.

The agency's Office of Defects Investigation received three complaints alleging a loss of brake power assist due to the failure of a brake vacuum pump involving the 2012 model. The investigation covers units manufactured between 2010 and 2017.

According to the agency's May 10 report, an inoperable brake vacuum pump may result in increased stopping distance, hence increasing the risk of a crash.

Mitsubishi Motors Corp. conducted recalls in 2013 and 2014 to fix the problem but the agency received the complaints between March 2018 and March 2019, or about five to six years after the pumps were replaced.

The agency opened a recall query to assess the failure frequency of the replacement pumps.