Want to change the air filter on your 2004 to 2011 Ford Focus? Replacing an air filter is normally no big deal on most cars. A replacement air filter typically sells for $20 or less. But on 2004 to 2011 Ford Focus PZEV models, the air filter housing is sealed and the filter element is not replaceable. If your car needs a new filter, you have to replace the entire sealed housing. They call this the $500 service surprise, because that's how much a Ford dealer charges for a replacement air filter housing (plus installation labor)!.
Why would Ford use such an expensive filter? The short answer is to meet Partial Zero Emission Vehicle (PZEV) emissions anti-tampering requirements. It also reduces maintenance costs (until the filter needs to be replaced), but it makes the car damn expensive to maintain when the filter becomes clogged and has to be replaced.
Ford says the normal service life of the air filter is 150,000 miles. The key words here are "normal service." Driving on gravel roads is probably NOT the kind of normal service Ford had in mind when they specified a 150K mile service interval for this air filter. The actual life of the filter will depend on driving conditions and how much dust is sucked into the housing.
Air Flow Restriction Gauge
The air resonator housing has a small round air flow restriction gauge to monitor the condition of the air filter. As the filter element becomes clogged, the gauge reading will change from GREEN (OK) to RED (filter is obstructed and overdue for a change). The filter should be replaced BEFORE the gauge goes to red because a restricted air filter will hurt performance, fuel economy and emissions.
Replacing the Air Filter
If you want to maintain emissions compliance and help maintain the profitability of Ford Motor Company, you can buy a original equipment replacement air filter housing from your local Ford dealer. But expect to pay $460 to $470 for the sealed replacement filter.
The Ford air filter parts numbers are as follows:
2.0L engines use filter part number 4S4Z9600AA
2.3L engines use filter part number3S4Z9600BE
The air filter housing can be replaced as follows:
1. Disconnect and removing the upper air resonator assembly.
2. Disconnect the MAF sensor wiring harness
3. Remove the MAF sensor pipe clamp-to-frame bolt
4. Remove the 8 screws and the Left hand fender well splash shield
5. Remove the air inlet tube bolt
6. Loosen the clamp and remove the inlet pipe
7. Remove the rearward air cleaner-to-frame bolts
8. Remove the forward air cleaner-to-frame bolt
9. Remove the sealed air cleaner housing and MAF sensor pipe as an assembly
To install, reverse the above procedure.
Replace the Stock Sealed Filter Housing with an Aftermarket Cold Air Intake System
If you think this is a ridiculous price to pay for an air filter for an "economy" car, your other option is to remove the air filter housing and air restrictor box and replace them with an aftermarket cold air intake system. Various brands and styles are available, and most can be had for $150 or less. The benefit of replacing the sealed air filter with an aftermark4t cold air intake is that the filter element can be easily replaced (usually for less than $30), and you typically gain about 5 horsepower from eliminating the restriction created by the stock intake system. The downside is that an aftermarket intake system on the Ford Focus PZEV is NOT legal for street use in California and other states that have adopted CARB PZEV emission rules. If nobody looks under the hood, your car will still pass an emissions test. But if they get nit picky, your car may be failed for "emissions tampering."