Common Reasons Your Car's Engine Is Knocking - Carr Subaru Service Answers

A knock is a simple, nonverbal method of communication. In most cases, it tells you that someone is at the door (or that the person in the apartment below yours doesn't appreciate your late-night tap dancing practice). If you hear a knocking from the engine of your Subaru, your engine is communicating with you--but it doesn't have good news.

At Carr Subaru, we're dedicated to helping you learn about Subaru problems and service. That's why we've put together this page of information on four potential causes of a knocking sound coming from your engine. Whatever's causing it, though, we recommend scheduling a service appointment as soon as possible.

Fuel pumps showing gas with different octane ratings.

4. You Put the Wrong Fuel in Your Subaru

If your Subaru requires a higher-octane fuel, and you've given it a lower-octane one, it could cause the knocking sound. Make sure to check with your owner's manual, which will tell you the right octane level. If you've accidentally made this mistake, it might help to add an octane booster to the tank. If this clears things up, just be sure to fill the tank with the right kind of gas next time.

A person inspects fuel injectors on the rail.

3. The Combustion Chamber Has Carbon Buildup

Even though the gasoline you put in your Subaru is treated with detergents that help keep your engine clean, it can still cause carbon buildup over time. While adding fuel injector cleaner may help some, it's a better idea to get a professional fuel injector cleaning service performed.

Three spark plugs outside of a vehicle.

2. Spark Plug Problems

If your Subaru has issues with its spark plugs, knocking could be a result. This could be due to your old spark plugs being replaced with the wrong type of new plug, or it could be that the spark plug gap has worn too large over time--among other things. Whatever the problem, bad spark plugs can ignite the fuel-air mixture at the wrong time, causing a knocking sound in the engine of your Subaru.

1. A Bad Knock Sensor

The knock sensor is meant to prevent knocking in the engine; however, if things go wrong, it can actually cause it. When it's working as it should, the knock sensor will sense when a knock is happening, and then tell the computer to adjust the timing to keep the knock from continuing. However, a damaged knock sensor may tell the computer to adjust the timing even if the engine is functioning regularly--which can lead to more knocking.

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  1. Carr Subaru

    11635 SW Canyon Rd
    Beaverton, OR 97005

    • Sales: (877) 271-4560

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Carr Subaru

11635 SW Canyon Rd
Directions Beaverton, OR 97005

  • Sales: (503) 672-3370
  • Service: (866) 460-0188
  • Parts: (888) 627-4707