Bad Knock Sensor Symptoms, Causes, and Replacement Cost

In a car engine, there are various sensors responsible for regulating different functions, such as ignition timing, emissions, and temperature. Knock sensor is one of the most important engine sensors. Learn the symptoms of a bad knock sensor.

The main function of the knock sensor is to prevent engine damage caused by pinking, spark knock, pinging, or detonation. It is typically found on the engine block, cylinder head, or intake manifold.

If you care about the longevity of your engine, it’s essential to pay attention to knocking and vibrations coming from the engine. Being able to detect symptoms of a faulty knock sensor is vital in maintaining your engine’s health. This article explains the bad knock sensor symptoms, causes, and replacement cost.

Symptoms Of A Bad Knock Sensor

The check engine light illumination is one of the clear symptoms of a bad knock sensor. A bad knock sensor can lead to engine pinging or knocking in extreme cases, but most of the time, you’ll observe issues like poor fuel efficiency and reduced engine power.

Let’s discuss the bad knock sensor symptoms in detail:

1) Check the Engine Light Illumination

If the check engine light comes on, it doesn’t always mean the knock sensor is bad, but it could be the cause. There’s a chance that your car’s engine is knocking. No matter the reason, if the check engine light is illuminating, you should look into it.

To find out the specific issue, you need to read the engine code with a diagnostic tool. This will help pinpoint the exact issue and guide you on what needs to be fixed.

Read More: How To Reset Check Engine Light?

2) Loss of Fuel Economy

Whenever your engine goes back to its basic settings, it doesn’t perform at its best.

If the knock sensor is not working properly, it not only makes the car slower and less responsive but also causes it to use more fuel than usual.

Although you may not notice a significant change, you’ll maybe see a slight reduction in miles per gallon.

Read More: Causes of Poor Gas Mileage

3) Knocking Noise

The engine knocking is one of the clear symptoms of a bad knock sensor. This bad sensor noise is like a loud thumping noise coming from the engine.

If you continue driving without fixing the main issue, the noise will get louder. The knocking noise usually appears inside the engine cylinders because the ignition of the fuel-air mixture is not happening at the right time.

4) Poor Engine Power

When the knock sensor in your car is not working properly, it not only affects how fast the car can go but also reduces its power and ability to handle heavy loads. In simple terms, it impacts both the torque and the top speed of your vehicle.

This is because the knock sensor plays a critical role in monitoring engine performance and preventing excessive force that could lead to damage. When the knock sensor detects abnormal engine conditions, it forces the engine control module (ECM) to revert to default values, which may reduce performance to safeguard the engine from potential harm.

As a result, the car’s engine power is reduced due to the faulty knock sensor.

5) Poor Acceleration

A bad knock sensor may also lead to poor acceleration. When the knock sensor of your car fails, it can’t help the engine control module (ECM) of your car to optimize engine performance properly. As a result, you will experience a reduction in the vehicle’s speed.

This is because the pressure produced in the engine cylinder is not fully utilized, leading to lower torque and causing acceleration problems. Poor acceleration is a frequent sign of a faulty knock sensor in a Hyundai car.

Causes of a Faulty Knock Sensor

Wrong timing of the spark that ignites the fuel in the engine.
Carbon accumulation within the engine cylinders.
Contaminants getting into the engine cylinders.
An issue with the spark plugs that don’t work properly.
The fuel and air mixture is not balanced correctly.
Using spark plugs that are not suitable and have deposits on them.
Using low-quality fuel.
Wrong installation of the knock sensors.
Wrong spark plug gaps.
Engine overheating.
Physical damage to engine components.

Knock Sensor Function

The main function of the knock sensor is to monitor the unusual sounds from the engine and transfers this data to the ECM or PCM of your car. These unusual sounds producing from the engine are called knocks. The knocking sound should prompt you to conduct troubleshooting to identify and address the root problem.

When the knock sensor monitors an issue in your engine, it triggers the check engine light to come on. Additionally, it automatically decreases the engine’s power to prevent any potential damage to your car.

This feature is helpful in preventing damage, but it can be tricky because a bad knock sensor may show similar symptoms as an actual knock in the engine.

So, before assuming you have a bad knock sensor, it’s essential to check if there is a real knock issue in your engine. Some knocks are not very loud, so if you’re not sure, it is recommended to consult a professional to inspect and diagnose the problem of your vehicle.

Knock Sensor Location

The knock sensor can be found in a few different positions on your car, but the most common ones are on the intake manifold, cylinder head, or engine block. It’s usually connected to the exterior of the engine block, but sometimes it can be positioned under the intake manifold.

Since the location of the knock sensor can vary, it’s helpful to know where to look before you start searching for it.

To locate the specific knock sensor in your car, it is recommended to consult your owner’s manual or visit a parts website. This will help you know where to find it and make the process of finding and replacing it much simpler.

Knock Sensor Replacement Cost

The knock sensor replacement cost varies according to your car model and the labor cost.

The average replacement cost of a knock sensor is from $240 to $370. Remember that this cost is for replacing a faulty knock sensor, not for fixing an engine knock issue.

How To Replace A Knock Sensor

FAQ Section

What does engine knock sound like?

Engine knock usually sounds like a clicking, pinging, or knocking noise originating from the engine. This noise may get louder when you press the gas pedal or accelerate the vehicle.

What does a knock sensor do?

A knock sensor is like the ears of your car’s engine. It monitors any unusual sounds within your engine, like detonation and pre-ignition occurring within the engine cylinder. It helps prevent engine damage by adjusting the ignition timing when it senses these issues.

Is it easy to replace a knock sensor?

In certain car models, the process of changing a faulty knock sensor is relatively simple, requiring minimal engine disassembly for access. But in most newer car models, replacing a malfunctioning knock sensor can be quite challenging. It often involves removing multiple engine parts before gaining access to the sensor, making it a laborious and intricate task.

Can a bad knock sensor cause a knock in the engine?

Yes, a faulty knock sensor is one of the major reasons of knocking sound inside the engine.

What does a bad knock sensor sound like?

When you have a bad knock sensor, your engine may produce a loud thumping sound.

Is it safe to drive with a bad knock sensor?

Driving with a bad knock sensor can cause your car’s engine to run hot, leading to increased emissions, which may exceed the Environmental Protection Agency’s (EPA) allowable limits. To address this issue and maintain compliance, a decreased acceleration safety feature has been designed to limit engine performance and prevent excessive emissions.

Can a bad knock sensor cause rough idle?

Yes, a faulty knock sensor may lead to rough idling. The knock sensor of your vehicle detects engine vibrations and noises caused by detonation or pre-ignition. When it becomes faulty, it may cause wrong ignition timing and result in a rough or poor idle.

Can a faulty knock sensor cause a misfire?

Yes, a defective knock sensor may lead to a misfire. The misfiring occurs when the engine control unit (ECU) of your car receives inaccurate data from the knock sensor, causing improper adjustments to the engine timing, which in turn can result in misfires.

Can a knock sensor damage the engine?

Absolutely! If you ignore a bad knock sensor and don’t fix it, it can harm the engine.

Can you drive with a bad knock sensor?

Yes, driving with a bad knock sensor is possible, but it is not recommended. Driving with a bad knock sensor may lead to different drivability issues, such as an increase in exhaust emissions, poor fuel economy, or poor engine performance.

How long can I drive with a bad knock sensor?

The duration of driving with a bad knock sensor depends on the problems it’s causing. If your engine is making knocking sounds when you accelerate, driving it for too long may lead to the failure of the valves and pistons. There’s no fixed time limit, but addressing the issue promptly is important to avoid potential damage.

Written By

Engineer Rahela

Rahela is the owner and main author of Mechanicalspecial. She is an automotive expert writer. She have over four years of experience in the automotive writing niche and have completed over 700 pieces of content from 40 projects. She have good knowledge and skill in vehicle repairing, all mechanical work, car upgrades and maintenance.