Skip the auto shop - Our mechanics make house calls

Symptoms of a Bad or Failing Fuel Filter (Auxiliary)

fuel filter

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.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Skip the repair shop, our top-rated mechanics come to you.

At your home or office

Choose from 600+ repair, maintenance & diagnostic services. Our top-rated mechanics bring all parts & tools to your location.

Fair & transparent pricing

See labor & parts costs upfront, so you can book with confidence.

12-month, 12,000-mile warranty

Our services are backed by a 12-month, 12,000-mile warranty for your peace of mind.

Get A Quote

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!

Need Help With Your Car?

Our certified mobile mechanics make house calls in over 2,000 U.S. cities. Fast, free online quotes for your car repair.


Post a question and get free advice from our certified mechanics.


More related articles

How Long Does a Throttle Return Spring Last?
Not all vehicles on the road feature an electronic throttle control (ETC), which is also called drive-by-wire. For vehicles that don't offer this system, they have a throttle cable instead that...
P0052 OBD-II Trouble Code: HO2S Heater Control Circuit High (Bank 2 Sensor 1)
P0052 code definition HO2S Heater Control Circuit High (Bank 2 Sensor 1) What the P0052 code means This code is seen when the Engine Control Module (ECM) tries to control the...
The Traveler’s Guide to Driving in Malaysia
CraigBurrows / Malaysia is a popular destination for many tourists today. The country has amazing sights and attractions that you will want to explore....

Related questions

Q: I have a 1998 lexus gs4oo. I was driving it, and all of a sudden it started to die on me, it didn't die all of a sudden ,it kinda

There are a couple of sensors in your car that regulate the flow of fuel and air into the car's engine. One is called a mass air flow sensor. This regulates the air flow into the car's engine to make...

Q: Mustang started and then died

There can be a large variety of reasons as to why your Mustang is not starting. When you add to the equation that it has been sitting for a couple of years, it may mean your Mustang is facing multiple...

Q: not starting

The first thing to check is to see if you have fuel pressure at the fuel injector fuel rail. Sometimes the fuel filter housing will block fuel from coming from the fuel tank and blocks the fuel from getting through...