Nissan has determined that if a sufficiently hot object [for example, a cigarette ash or other ignition source] enters the air filter housing through the engine fresh air intake system and contacts the air filter, the flammability characteristics of the air filter material are such that the filter may ignite," the NHTSA said on its Web site. "If the air filter ignites, a fire may occur."
Vehicles built after the aforementioned dates are equipped with a different air filter.
Source:
Edmunds.com