Nissan is recalling more than 47,000 Leaf electric cars in the U.S. and Canada, citing a possible brake malfunction. Documents posted by U.S. safety regulators Saturday say the problem is centered on a relay inside the cars' electronic brake booster. Very cold temperatures can cause the relay to fail, requiring more driver effort to operate the brakes. That could increase the risk of crashing. No accidents or injuries have been reported to Nissan.The automaker will notify owners who need repairs. Dealers will reprogram software that controls the recalled cars' brake control, free of charge. The recall includes 46,859 Leafs in the U.S. and another 679 in Canada from the 2013 through 2015 model years. The models in the recall were manufactured between Nov. 19, 2012 and July 31.