DETROIT (AP) — U.S. auto safety regulators are investigating complaints that more than 540,000 Ford pickup trucks can abruptly downshift to a lower gear and increase the risk of a crash.

The National Highway Traffic Safety Administration says in documents posted on its website Friday that it opened the investigation this week after receiving 86 consumer complaints about the problem with the trucks’ automatic transmissions.

Investigation documents say the probe covers F-150s from the 2014 model year. The agency is looking into whether those trucks should have been included in previous recalls for the problem.

The complaints allege that the trucks can suddenly shift to a lower gear without warning. Often, the rear wheels locked up, with one consumer telling the agency that his truck downshifted abruptly, causing it to crash into a concrete barrier and another vehicle. Both the pickup driver and the driver of the other vehicle were hurt.

The company said it’s working with NHTSA to support the investigation. Ford’s F-Series pickups are the top selling vehicles in the U.S.

Certain F-150 pickups from the 2011 and 2012 model years were recalled for the same problem in 2016. Ford later added 2013 models to the recall.