An air pump, also commonly referred to as a smog pump, is an emissions component that is part of the secondary air injection system. It is responsible for pumping clean air into the vehicle’s exhaust stream to promote a cleaner and more complete burn before the fumes exit the tailpipe. By injecting clean air into the exhaust, the amount of hydrocarbon pollutants produced by the vehicle is reduced, as the entire system is finely tuned to run with the air provided by the air pump.

When it fails, the overall performance of the engine may suffer due to the lack of air. Many states also have strict emissions regulations for their road going vehicles, and any problems with the air pump or the air injection system can not only cause performance problems, but also cause the vehicle to fail an emissions test. Usually, a failed air pump will produce a few noticeable symptoms that can alert the driver that the vehicle requires attention.

1. Engine is running rough

One of the first symptoms of a bad or failing smog pump is a rough running engine. When a smog pump fails the finely tuned air-fuel ratios can be upset, and it will negatively affect the performance of the engine. The engine may have trouble idling, and may drop in engine speed, or stall when the pedal is pressed.

2. Reduced horsepower

Another common symptom of a bad air pump is a reduction in power output from the engine. Again, a failed smog pump can upset the tune of the vehicle, which will negatively impact overall engine performance. A failed air pump may cause the engine to hesitate or stumble on acceleration, and in more serious cases, cause a noticeable reduction in total power output.

3. Check Engine Light comes on

Another symptom that may be indicative of a bad air pump is an illuminated Check Engine Light. This will usually only occur after the computer has detected the air pump has completely failed, or an electrical problem with the air pump circuit has occurred. A Check Engine Light can also be caused by other problems, so it is important to have the computer scanned for trouble codes before making any repairs.

The air pump is an important component of the emissions system, and necessary to keep your vehicle running in proper order so that it can meet the proper emission requirements. If you suspect that your air pump may be having a problem, or your Check Engine Light has come on, have the vehicle diagnosed by a professional technician, such as one from YourMechanic. If necessary, they will be able to replace the air pump and restore proper performance to your vehicle.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Air Pump and was authored by Ed Ruelas.


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