After receiving notice of additional consumer complaints the National Highway Traffic Safety Administration added thousands of Fusion and Lincoln MKZ vehicles to an ongoing investigation into door latches that may inadvertently open while the car is in motion.

The Detroit News reports NTHSA’s investigation now covers nearly 486,000 model year 2011 to 2013 Fiesta and model year 2013 Fusion and Lincoln MKZ vehicles.

The inclusion of the Fusion and Lincoln models occurred after Ford reported it received 11 complaints related to improperly closing doors in the vehicles which utilize the same door latches as the Fiesta models already under investigation.

In addition to increasing the scope of the investigation, regulators upgraded the probe to an engineering analysis – a step that can sometimes lead to a recall.

The agency says in a notice [PDF], that the upgraded investigation was initiated to “further assess the scope, frequency and consequence of this failure.”

The added scrutiny comes after NHTSA received 207 reports related to improperly latching doors. Sixty-five of those reports claimed that the door or doors opened inadvertently while the vehicle was in motion.

The agency says it was also notified of two injuries caused by a “rebounding door striking a consumer after they attempted to close it.”

When NHTSA originally launched an investigation into the Fiesta models last year, the agency had accumulated 61 reports of potential door latch failures, of which 12 allegedly occurred while the vehicle was in motion.

Since then, Ford has provided the agency with 451 additional reports and 1,079 warranty claims related to door latch failures.

In a response to NHTSA’s inquiry, Ford said that it does not believe that a latched door experiencing this condition will inadvertently unlatch and that there are many overt warnings associated with a door that does not latch.

Still, regulators say the “rate of occurrence for this failure is comparable to other door latch failure investigations” and that the agency “questions the effectiveness of warning signals given the number of complainants alleging that the door(s) opened while the vehicle was in motion.”

A spokesperson for Ford says the company is cooperating with the investigation.

U.S. upgrades Ford Fiesta door latch probe [The Detroit News]

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