The U.S. auto safety regulator on Friday said that it has opened a preliminary investigation into more than 200,000 diesel trucks of Ford Motor Co. (F  ) following multiple complaints of a fuel leak that may result in fires.

What Happened: The National Highway Traffic Safety Administration (NHTSA) said that it received 27 complaints alleging diesel fuel leaks in the model year 2015-21 Ford F-250, 350, 450, and 550 Super Duty vehicles equipped with 6.7-litre diesel engines. Of the 27 complaints received by the regulator, 12 complaints described an engine compartment fire, with four injuries reported due to the issue.

The leaks are due to a fracture in the secondary fuel filters manufactured by Allevard Sogefi USA, the regulator said, while adding that the close proximity of the fractured filter with high heat sources may cause a fire.

The preliminary probe is aimed at assessing the severity of the potential problem and identifying the safety risks posed by it, the regulator said.

Why It Matters: This comes after the company issued a recall in March for over 42,000 model year 2022-2023 Ford Bronco Sport and model year 2022 Ford Escape vehicles equipped with 1.5L engines, citing similar concerns of a fuel leak causing under hood fire.

Last month, the NHTSA opened an investigation to evaluate the adequacy of the remedy deployed by the company for the recall as it did not replace the cracked fuel injector but only installed a drain tube and an engine control software update.

As per data from NHTSA, Ford has issued 23 recalls this year, the most among automakers- potentially affecting about 2.9 million vehicles.

In comparison, General Motors (GM  ) has issued 7 recalls while Stellantis (STLA  ) has issued 21 in the United States.