CNN  —  Ford is recalling more than 550,000 F-150 pickups in the United States because of an issue that can cause the transmission to suddenly and unexpectedly, at any speed, shift down to first gear. These trucks have six-speed transmissions. Usually, first gear is used to drive a vehicle at very low speeds, so suddenly shifting to first gear at high speed could cause the truck to slow rapidly or even cause the driver to lose control. The trucks involved are older models from the 2014 model year. The problem with these particular trucks first came to Ford’s attention in February of this year, though, as the automaker received a number of reports of 2014 F-150s suddenly downshifting at the wrong time. In 2019, Ford recalled roughly 1.2 million model year 2011 through 2013 F-150s for the same issue. The problem results from a loss of signal between a speed sensor and a control module that operates the automatic transmission. To fix the problem, Ford dealers will update the trucks’ control module software at no cost to the owner. Ford will start mailing letters to owners of the trucks involved in a few days. Customers with questions can call Ford customer service at 866-436-7332 and ask for information about recall number 24S37.