Virtually all vehicles equipped with gasoline engines are equipped with fuel filters that are meant to filter out any dirt or debris that could contaminate the fuel system or damage the components, and possibly even the engine. Some vehicles will come equipped with a second fuel filter, known as the auxiliary fuel filter, that serves as an additional filter to further protect the fuel system components and engine. When the filter becomes excessively dirty or clogged, it can cause issues engine performance issues. As the auxiliary fuel filter functions in the same manner as the primary fuel filter, the symptoms associated with it when it fails are similar to that of a regular fuel filter. Usually a bad or failing fuel filter will produce a few symptoms that can alert the driver of a problem.

1. Car is hard to start

One of the first symptoms of a problem with the auxiliary fuel filter is hard starting. If the filter becomes excessively dirty or clogged it may restrict fuel pressure or flow, which may cause the vehicle to experience difficulty starting. The problem may especially noticeable at cold starts, or after the vehicle has been allowed to sit for a while.

2. Engine misfires or decrease in power, acceleration, and fuel efficiency

Engine performance issues are another symptom of a problem with the auxiliary fuel filter. If the fuel filter becomes excessively dirty to the point of seriously restricting the flow of fuel, it may cause the vehicle to experience drivability issues such as misfires, a decrease in power and acceleration, poor fuel economy, and even stalling. The symptoms will usually continue to get worse until the vehicle can no longer run, or start.

3. Check Engine Light comes on

An illuminated Check Engine Light is another possible symptom of a faulty auxiliary fuel filter. Some vehicles come equipped with fuel pressure sensors that monitor the pressure and flow of the fuel system. If the fuel filter becomes excessively dirty and restricts the flow of fuel, and it is detected by the sensor, the computer will set off the Check Engine Light to alert the driver of a potential issue. The Check Engine Light can also be set off by a wide variety of other issues, so having the computer scanned for trouble codes is highly recommended.

While they are not found on all vehicles, auxiliary fuel filters are another important routine maintenance component that should be changed at the recommended intervals in order to keep the engine running in proper order. If you suspect that your auxiliary fuel filter may be having an issue, have the vehicle inspected by a professional technician, such as one from YourMechanic, to determine if the filter should be replaced.

This article originally appeared on YourMechanic.com as Symptoms of a Bad or Failing Fuel Filter (Auxiliary) and was authored by Eduardo Ruelas.


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