WASHINGTON (Reuters) - Ford Motor Co F.N said on Thursday it would recall 2 million F-150 pickup trucks in North America because of a seat belt problem that could generate excessive sparks and cause fires.

The second-largest U.S. automaker said it received 17 reports of smoke or fire in the United States and six in Canada but was not aware of any injuries.

During a crash, a device called a pretensioner uses an explosive charge to lock the seat belt in place. The company said the device may generate excessive sparks.

Ford will fix the problem for free and said in a securities filing the recall would cost about $140 million. The company said the cost would be reflected in third-quarter earnings but Ford left unchanged its guidance for full-year 2018 adjusted earnings.

The recall covers 2015-2018 Ford F-150 Regular Cab and SuperCrew Cab vehicles in North America for driver and front passenger seat-belt pretensioners.

Ford said the recall included 1.62 million U.S. vehicles, 340,000 in Canada and 37,000 in Mexico.

Shares of the company closed down 0.5 percent at $9.45.

To resolve the issue, dealers will remove some insulation material and remnants of wiring harness tape from the vehicle’s B pillar area, and apply heat-resistant tape to the carpet and its insulation. They will also modify the back interior panels of Regular Cab vehicles. The B pillar is the vertical support behind a vehicle’s front seat windows.

The recall came just weeks after the National Highway Traffic Safety Administration (NHTSA) opened a preliminary investigation in August after five complaints of fires in the seat belt component, including three vehicles destroyed by fires. The agency had asked Ford about fire reports earlier this year.

A Ford spokeswoman said the company “identified this issue through its normal quality processes.”

Transport Canada, the Canadian auto regulatory agency, contacted Ford in November 2017, regarding a B-pillar area fire on a 2015 vehicle. That prompted a joint vehicle inspection by Ford and the agency, but the cause could not be determined.

Ford also reviewed four reports of post-crash interior fires earlier in 2017 in the B-pillar area of trucks, but did not find any issues.

Ford said the components in the older 2015-2017 models were built by Takata, which was acquired by Ningbo Joyson Electronic Corp 600699.SS, while ZF Friedrichshafen AG [ZFF.UL] built the parts starting with the 2018 model year.

German auto supplier ZF said it was working with Ford on the recall and Ningbo Joyson did not immediately respond to a request for comment.