U.S. safety regulators have opened a probe of an estimated 218,000 Mercedes C-class sedans after receiving consumer complaints claiming a failure of rear turn signals and brake lights.

The U.S. National Highway Traffic Safety Administration opened a preliminary evaluation of the luxury cars from model years 2008 and 2009 after receiving 21 complaints from U.S. consumers.

A spokesman for Mercedes, a unit of Germany’s Daimler AG, did not have an immediate comment.

The reports typically said the failure is with the lamp connector, with many indicating burnt or melted electrical components, according to NHTSA documents. In multiple instances, consumers have reported smelling smoke and seeing burn marks in the trunks of the cars, with one reporting small flames emanating from the rear lamp connector, NHTSA said.

A preliminary evaluation is the first step in a process that could lead to a recall should regulators determine that a safety issue needs to be addressed by a manufacturer.