On certain Ford Focus vehicles, the original air cleaner assembly is said to be a lifetime unit. It's a fairly complex piece that's fed by a carbon arrestor and features a restriction gauge like the one found on many diesel engines. The air cleaner itself features internal baffling and multiple layers of foam designed to filter air progressively. The filtration media, however, can require replacement, especially if the vehicle is used in dusty or dirty conditions, but Ford sells only a complete assembly that costs hundreds of dollars that features the same high-tech (but unserviceable) filtration media. This OE FIX air filter housing has been redesigned to interface between the carbon arrestor and throttle body just like the OE unit, but it accepts a standard paper air filter (included) to enable faster, more affordable and more frequent future service to prolong engine life.