DETROIT -- The U.S. government's road safety agency has closed a more than six-year-long investigation into exhaust odors in Ford Explorer passenger cabins, determining the SUVs don't have high levels of carbon monoxide and don't need to be recalled.
The National Highway Traffic Safety Administration says the agency reviewed more than 6,500 consumer complaints, tested SUVs in the field, and called in automotive, medical, environmental health and occupational safety experts before making its determination.
The probe covered nearly 1.5 million Explorers from the 2011 to 2017 model years. NHTSA said it received multiple complaints of sickness and crashes caused by the exhaust fumes that involved three deaths and 657 injuries. Many complaints came from police departments that used Explorer Police Interceptors as patrol vehicles.
But the agency said in documents released Monday that it used rigorous test methods to send exhaust gas into vehicles. No Explorers with bodies that were sealed under a 2017 Ford field service campaign had carbon monoxide levels that were higher than Environmental Protection Agency limits.
The agency, though, conceded that fumes had leaked into the Explorer cabins. "NHTSA recognizes that hypersensitivities to CO and other exhaust gas constituents exist within the overall population," investigators wrote. "However, the agency does not set limits or determine the adequacy of established safe levels."
The agency determined that sealing issues caused by installing sirens, lights, cages and other items on police SUVs were responsible for the highest measured carbon monoxide levels in vehicles it tested. The highest carbon monoxide levels in consumer vehicles were usually traced to sealing issues caused by repairs after rear crash damage, NHTSA said.
Even without Ford's sealing repairs, no vehicles without crash damage or police equipment installed had carbon monoxide levels that exceeded acceptable levels, the agency wrote. "Therefore the agency has not identified a defect that represents an unreasonable risk to motor vehicle safety," the agency wrote.
The agency said it had received thousands of reports saying odors in the vehicle triggered a variety of responses, largely nausea, headaches and light-headedness. NHTSA said it focused its investigation on accurately measuring vehicle carbon monoxide levels and carboxyhemoglobin levels from "properly administered blood tests."
In a statement Monday, Ford said it was pleased the investigation found no unreasonable risk to vehicle safety. "Ford's previous investigation and extensive testing determined the same results, which we have always maintained," according to the company.
At first Ford offered sealing repairs only for emergency vehicles, but later the automaker expanded the repairs to civilian versions after thousands of complaints about fumes leaking into passenger cabins. Mechanics at dealers were to check for leaks in the rear lift gate gaskets and drain valves. If leaks were found, they were sealed to prevent fumes from entering the cabin. The heating and ventilation systems were also reprogrammed to let in more fresh air.
Even after the repairs were made, NHTSA continued to receive complaints about exhaust odors inside the Explorers.
At one point in 2017, the Austin, Texas, police department removed 400 Explorer Police vehicles from service over concerns of carbon monoxide in the cabins. But the department put them back on patrol after Ford made repairs to exhaust tips and lift gates, and fixed other issues.
NHTSA also said it investigated cracked exhaust manifolds and tested the service campaign repairs to make sure they didn't affect cabin fume levels.
The nonprofit Center for Auto Safety in Washington in 2018 had called on Ford to recall all of the Explorers. On Monday, Center for Auto Safety Executive Director Michael Brooks said Ford's service campaign appears to have remedied the issue, but he questioned why NHTSA took so long to examine the complaints and make a decision.
He also said NHTSA should seek recalls of all Explorers with crash damage to make sure the bodies are sealed.