Bad Knock Sensor Symptoms


Some people have the experience of driving and their car’s engine just doesn’t feel right. They can’t identify the problem but something just seems off. They could have a bad car knock sensor

Bad knock sensor symptoms include a lack of acceleration or loss of power, lost fuel mileage, and the check engine light appearing. 

Do you wonder what the car knock sensor does and how it affects your vehicle? Read on to find out more and learn when to take your vehicle to the shop. 

What Is a Car Knock Sensor?

Modern cars are far more computerized than those of previous years and part of the new technology are sensors. Sensors control many important functions within your vehicles like ignition timing, transmission shifting, emissions, and fuel economy. 

The knock sensor detects noises within your engine. It can be described as your vehicle’s ear.

Specifically, the car knock sensor listens for noises that come about from combustion, or which fuel is fired in the cylinder of your engine. 

Beyond listening for detonation noises, the car knock sensor adjusts ignition timing to accommodate the combustion it hears. 

A malfunctioning car knock sensor means that combustion in the engine isn’t regulated property and neither is the ignition timing. If left unchecked, your car could end up with significant engine damage. Identifying symptoms of a faulty knock sensor will help you get it replaced sooner and that will save money on expensive repairs later. 

Read: 5 Reasons Why A Car Engine Knocks On Startup Then Goes Away

Symptoms of a Bad Knock Sensor

There are some distinctive symptoms when your knock sensor starts to fail. Here are the main signs.

Engine Feels Odd

This symptom is hard to explain because there isn’t a concrete symptom to describe. It could be the way the car moves or sounds coming from the engine. 

Sounds can be a significant reason why drivers become concerned about their car and say it doesn’t feel right. Noises coming from your engine are a clear sign that you could have a malfunctioning knock sensor. 

Noises will probably be more of a loud thumping sound. It may not sound loud at first but gets louder after you drive for a while. The noises are created by fuel and air igniting improperly inside the cylinder and not reaching a point of combustion. 

Lack of Acceleration

An obvious sign of a bad car knock sensor is a loss of acceleration. This typically happens when you try to reach highway speeds. It may also hesitate, jerk, or even feel like it’s dragging. 

This can be a symptom of other problems too but any problem that occurs while you are on the road should be checked out. 

Loss of Power

Your vehicle may also experience a loss of power when it has a bad car knock sensor. It may suddenly slow down or not even run up to normal speeds without trying to accelerate. This is probably related to either the car knock sensor or one of the other sensors associated with air intake or fuel injection.

Bad Fuel Economy

Typically, any problem that involved combustion or ignition is going to result in bad fuel economy. That’s because the car tends to try to make up the difference in a combustion issue by adding more fuel. 

The car knock sensor controls the air by adjusting the timing and that leads to the right amount of fuel being mixed in. When that goes bad, the car’s computer automatically just starts pumping fuel through the car to try to keep it running. The result is you will be visiting gas stations more. 

You should talk to a mechanic if you start to notice inefficient fuel economy because it could be the car knock sensor or one of the other sensors that have gone bad. Several are involved in the combustion process. 

Check Engine Light

Cars today are filled with dummy lights and one of the most common to come on to show any type of engine problem is the check engine light. This light is meant to give you a warning that something is malfunctioning in your vehicle. 

A mechanic will use a scanner to identify any error codes that caused the check engine light to appear. The code for a faulty car knock sensor is P0325. Even though that code indicates you have a faulty sensor, there could be another root reason the sensor is giving you issues. It will take a mechanic to fully diagnose the problem. 

A Bad Knock Sensor Causes Emission Problems

A faulty knock sensor can cause another problem: emissions. Your engine may run hot with a malfunctioning knock sensor and that can produce higher emissions. This means your car could fail emissions testing because it will go beyond what’s allowable by the Environmental Protection Agency (EPA). 

One of the features of many cars is a decreased acceleration safety feature. The feature was installed to accommodate EPA emission standards and low the rate of emissions if your engine isn’t performing well. 

The feature puts your car in low gear and speed until you get the engine issue fixed. Some people call this “limp mode” because it allows your car to run but not fast or with any time of high performance. 

The purpose is to slow your car down to keep emissions under regulations and to protect your engine from damage until you have repairs made. Most cars do not have a dashboard light that tells you that the car is using this feature and the feature is put into use automatically when the vehicle senses something is wrong with the engine. 

You will know you are in limp mode when you can’t go faster than a certain speed and the car will not go into the higher gears but otherwise runs fine.


Can I drive with a faulty knock sensor?

You can drive for a little while with a knock sensor malfunctioning but it isn’t wise nor enjoyable. Driving with a faulty knock sensor will mean your engine will be thumping and thudding. That will cause a lot of damage to your engine over time. Second, the constant sounds, jerks, and trouble accelerating along with other issues will make you not want to drive your car. 

Plus, you’re going to pay the price at the gas pump because you won’t get any fuel economy with a bad knock sensor.

The quicker you get your car to a mechanic the less it’s going to cost you in the long run. It may be a little upfront money now but it is a much more affordable solution when you compare that to more gas purchases and a possible engine repair that will come later.

How much does it cost to repair a knock sensor?

The cost to replace a knock sensor will be between $120 and $500 for most standard cars. Parts will cost between $65 and $200 and the labor will be between $50 and $350 at most shops. 

Can I disconnect the knock sensor?

Disconnecting the knock sensor will not fix your problem and will not tell you anything about what is going on with the car. Plus, you can end up with a severely damaged ending. 

A problem with the knock sensor will likely show up as an error code in the computer when you get a check engine light. It is typically P0325 which relates to circuit malfunction.

Can a bad knock sensor cause a transmission problem?

A malfunctioning knock sensor can cause transmission problems because it doesn’t relay the right time for the engine to fire the spark plugs. This causes a power loss and that can cause the transmission to use a different gear than it normally would to compensate. 

Over time, that can wear out the gears and cause damage to the transmission.

Can bad gas cause a knock sensor to fail?

No, but the two do have similar symptoms. Both bad gas and a blown knock sensor can cause rough idling, jerking, and knocking in the engine. 

However, bad gas and a malfunctioning sensor are not connected nor do they have the same effects over time.

Bad gas can be easily corrected by putting better gas in the tank with an additive. 

A faulty knock sensor is a part that just wears out over time or it may wear out sooner due to some other issue. Replacement is the only way to fix it as it will get worse and can severely damage your engine.

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