WASHINGTON U.S. auto safety regulators said on Saturday they are investigating Ford Motor's prior recalls of 710,000 Explorer SUVs over power loss reports to determine if the fix is adequate.

The National Highway Traffic Safety Administration said the No. 2 U.S. automaker issued recalls in April 2022 and March on Ford Explorer SUVs from the 2020-2022 model years to address a rear axle horizontal mounting bolt that may fracture and cause the driveshaft to disconnect.

Ford’s fix is to add a software update that automatically applies the electronic service parking brake to keep the vehicle from rolling away in the event of a driveshaft failure, the agency said, adding there is no remedy to address the failed rear axle horizontal mounting bolt "which is the basis of this safety issue and the cause of the impaired vehicle." NHTSA said it has received two complaints alleging a loss of power or transmission torque of the rear wheels in Explorer vehicles that had received the recall fix.

(Reporting by David Shepardson; Editing by Marguerita Choy)