Before the National Highway Traffic Safety Administration issues a recall, it leads in-depth investigations of the issue at hand.

This time the Ford Explorer utility vehicle is under scrutiny by the NHTSA. The administration is looking at a possible issue of the exhaust system that could cause fumes to spew in the cabin.

Ford Explorers manufactured between 2011 and 2015 are under investigation after the regulator got a number of no less than 154 complaints of exhaust smells filling up the passenger compartment.

Some of the complaints stated that carbon monoxide exposure could be to blame, and the risks associated with carbon monoxide are fatal. Looking at the content of the complaints, it looks as if the smell mainly occurs when the car is in full throttle. Other possible scenarios include the air conditioning being turned on and the HVAC system being set to recirculation mode.

The carmaker has issued two technical safety bulletins (TSBs) in regard to this problem. In the first one, Ford suggests that drivers seal and coat their rear floor pan and body seams and replace the air extractor. Installing new drain valves is also part of the carmaker's recommendations.

The second TSB underlines that a software update should also be loaded into the cars to handle the issue. By issuing TSB alerts, automakers message their service departments about specific problems and offer alternatives to resolving the issue. Keep in mind that some TSBs are unrelated to investigations or recalls, as they can pinpoint specific and benign issues.

According to the NHTSA, some of drivers saw no difference in the driving experience after the TSBs were issued.

Ford reached out to CNET and restated its determination to work with the regulators to solve the technical problems encountered by clients.

"We will cooperate with NHTSA on this investigation, as we always do," Ford says.

After the NHTSA closes its investigation, federal officials will decide whether a recall action is mandatory.

It is not the first time Explorer models went under NHTSA's magnifying glass. Back in June 2014, a similar problem was identified in the carmaker's SUVs. Two years ago, Ford issued a recall for its Explorer 2013 model after reports landed in about a stingy gasoline odor in and around the car, which was later determined to be connected with fuel leaks.

The autos that presented the issue had an imperfectly sealed seam at one side of the fuel tank.

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