The NHTSA investigation targets Mercedes C-Class sedans from 2008 to 2009.

The National Highway Traffic Safety Administration is taking a closer look at about 218,000 Mercedes C-Class sedans due to consumer complaints about faulty taillights that reportedly have caught fire in some instances.

NHTSA says it has so far received 21 separate owner complaints.  And though there have been no reports of injuries the potential for a more serious situation has federal safety investigators worried.

The most common complaint concerns brake lamps that have dimmed or won’t light up at all. Owners have reported noting the smell of smoke while others have noted that electrical components have melted.  Some have noted burn marks in the vehicle’s trunk while one owner reported seeing a small flame from a rear lamp connector when the trunk was open.

A story in the Detroit News notes that one owner’s complaint indicated the vehicle’s trunk was full of smoke and the smell of burning plastic, with heavy damage to the taillight’s electrical componentry. Another owner reported that a fire had destroyed part of the vehicle’s wiring harness but also noted that the local Mercedes dealer refused to make a repair under warranty.

The owner told NHTSA that, “This is a tremendous safety issue and I respectfully request that your agency address this matter with Mercedes.”

The 218,000 compact luxury sedans under investigation were all produced during the 2008 and 2009 model-years.

“We have recently begun working with NHTSA regarding this preliminary evaluation and can report that no injuries or deaths have been identified in this case,” Mercedes said in an official statement.  “Any customer with a tail lamp concern is invited to speak with Mercedes-Benz USA about the subject by calling 1-800-367-6372 or by contacting a local authorized Mercedes-Benz dealer to arrange an inspection.”

NHTSA opened its investigation on July 11. It has set no timetable for action and it will have to determine whether the problem is serious enough and clearly related to some sort of vehicle defect before deciding whether or not to order a recall.

While the extent of a problem can impact the government’s decision, NHTSA has this year ordered recalls covering as few as four vehicles, as happened when a total of four Chevrolet Volt plug-in hybrids were recalled due to a glitch with their electronic stability control systems. Another June safety campaign involved just 689 Aston Martins.

Other recent recalls have run into the seven figures, including last month’s campaign covering 1.5 million Jeeps which NHTSA alleged were at risk of catching fire in rear-end collisions.  The safety agency originally wanted to cover 2.7 million of the sport-utility vehicles but reached a compromise with Chrysler Group LLC after the automaker originally threatened to fight the order – which could have led to a lengthy court battle.

Fires, notably including those related to electrical problems, have become an increasing issue in the industry. Toyota last October approved the largest global recall in its history, involving a total of 7.43 million vehicles, due to defective power window switches that could short and cause a fire.

This past month, meanwhile, Honda recalled 143,000 Fit subcompacts due to a similar problem – in this case to re-repair the vehicles after an earlier Fix failed to prevent further short-circuits and fires.

The window switch fire has impacted a number of automakers and highlights the increasing use of common parts and components across a wide array of models, and even among otherwise competing automakers, in a bid to reduce costs.

It’s unclear if the taillight parts implicated in the Mercedes investigation are shared on other vehicles.