Ford Motor Co. is recalling about two million pickup trucks after it received reports of a seat-belt equipment malfunction that could cause smoke or fire, marking a setback for its top-selling F-Series product line that generates the bulk of its profit.

The Michigan-based auto maker said Thursday the recall is for F-150 vehicles between the model years 2015 through 2018. The vehicles were built at plants in Missouri and Michigan.

Ford said devices that automatically tighten passenger seat belts, known as pretensioners, “can generate excessive sparks when they deploy” and that it knows of 23 total reports of smoke or fire in North America, the bulk of which took place in the U.S.

Some seat-belt pretensioners use an explosive charge when the car’s sensors detect a sudden deceleration from an accident. That triggers a mechanism to immediately retract the belt and lock it into place, removing slack and helping to pull a front-seat occupant’s body back just before the impact, reducing injury risk.

Ford said its investigation determined excessive sparks generated by the devices in some trucks could ignite gases created when the pretensioner deploys inside the B-pillar, the vertical support that houses the seat belt. If that happens, insulation and carpet behind the pillar can catch fire, Ford said.