(AP) — U.S. highway safety regulators have opened an investigation into about a half-million semis with brakes that can catch fire. The National Highway Traffic Safety Administration says it has 11 complaints about brakes made by Haldex Commercial Vehicle Systems. There were seven reports of fires, but no injuries. The complaints say that problems occurred mostly on Kenworth and Peterbilt semis. The agency says it’s investigating problems with brakes from the 2015 through 2020 model years. The probe covers certain Haldex Gold Seal brake chambers, which convert compressed air into a mechanical force that stops the trucks. The brakes can drag and eventually cause fires. An investigation could lead to a recall. Messages were left Tuesday seeking comment from Haldex.