An air filter is like a security guard for your engine. It keeps the undesirables (dirt and debris) out while letting power-producing air in. A restricted air filter can cause many problems, including an illuminated check engine light.

Engine airflow performance

Besides keeping contaminants out, an air filter must allow unrestricted airflow into the engine. This is why air filter replacement is so important. An air filter that isn’t changed on a regular basis will become contaminated with dirt and debris. This prevents the proper amount of air from entering the engine. In extreme cases, a contaminated air filter can turn on the check engine light.

How a contaminated air filter can turn on the check engine light

An extremely dirty air filter restricts engine air intake. This disrupts the air/fuel mixture inside the engine. As a result, the vehicle may experience performance problems that trigger the check engine light. Here are some common examples:

• • Rich air/fuel mixture: Engine performance and operation is monitored by a computer, called the engine control module (ECM). The ECM monitors the level of oxygen in the exhaust via one or more oxygen sensors. When there is a lack of oxygen in the exhaust (a rich condition), the oxygen sensor will consistently send a signal to the ECM that’s above 450 mV. The ECM recognizes this is an abnormal condition that could affect vehicle emissions. In response, it turns on the check engine light (CEL).


• • Engine misfire: A misfire results from incomplete combustion inside the engine. A contaminated air filter can restrict engine airflow, resulting in a rich air/fuel mixture. This results in incomplete combustion and an engine misfire. A rich fuel mixture can also foul the spark plugs, causing a misfire.


• • An engine misfire can greatly increase vehicle emissions. For this reason, the ECM constantly monitors the engine misfire status. If it detects an engine misfire, it turns on the CEL.


• • Turbocharger performance: Turbocharger-equipped vehicles are particularly susceptible to clogged air filter issues. A turbocharger uses exhaust gases to force pressurized fresh air into the engine. A blocked air filter can prevent the turbocharger from building sufficient boost pressure. Since turbocharger performance is monitored by the ECM, lack of boost pressure can cause the ECM to turn on the CEL.


• • It should be noted that the air filter must be extremely restricted to turn the CEL on in a modern, naturally aspirated vehicle. This is because the ECM is good at compensating for lack of air flow.

Most modern vehicles have a mass air flow sensor (MAF) mounted downstream from the air filter. If the air filter becomes clogged, the ECM will adjust the air/fuel mixture, using input from the MAF. This smooths out engine performance and often prevents the CEL from being turned on. However, if the air filter is severely restricted, the ECM may not be able to compensate enough.

Keep the check engine light off with regular air filter maintenance

Regular air filter replacement prevents contamination that could turn on the check engine light. Exactly when a filter should be replaced depends on the filter manufacturer.

With Premium Guard air filters, you know you’re getting up to 12,000 miles of engine protection from dust and harmful particles. Premium Guard filters also provide a low-pressure drop, for maximum engine airflow. This keeps your engine performing its best and keeps the check engine light off.

Inexpensive peace of mind

No light is more unnerving than the dreaded check engine light. Keep your engine running right with regular air filter maintenance.

Sources: http://www.aa1car.com/library/check_air_filter.htm