Knock Sensor Symptoms, Causes, And Replacement Cost

A vehicle contains multiple sensors, each performing various tasks. These sensors help to optimize the performance of the vehicle engine. The knock sensor is also one of the major sensors of the vehicle. The knock sensor is essential because engine detonation can occur without it, causing significant damage to your engine. This article describes the bad knock sensor symptoms, causes, and how to replace it.

Symptoms of a Bad Knock Sensor

The engine knock is harmful to your engine’s health. The illuminated check engine light is one of the most common symptoms of a bad knock sensor. However, a bad knock sensor may also lead to some other symptoms such as poor acceleration, unusual noise, poor engine performance, poor fuel economy, or poor engine performance.

Let’s discuss these symptoms in detail:

1) Check Engine Light

The check engine light illumination is one of the most common signs of a faulty knock sensor. This light is located on your car’s dashboard.

However, the check engine light can be triggered by various factors such as a faulty EGR sensor, a bad O2 sensor, a bad MAP sensor, engine overheating, a faulty spark plug, low engine oil, and many others.

Therefore, when your vehicle’s computer triggers the check engine light, you must properly check all the engine parts and sensors to find the main reason for the illuminated check engine light.

2) Rough Idle

When the knock sensor goes bad, it may cause a rough idle. As this sensor becomes faulty, the PCM will be unable to get accurate data about unusual combustion events (knocking) occurring within the combustion chamber.

Because of the wrong information, your vehicle’s PCM may be unable to precisely adjust the air-fuel mixture or ignition timing, which could cause an unstable or rough idle.

However, there are many other factors that may lead to rough idle, but if your knock sensor is not working efficiently, it may also trigger this problem. Therefore, it is compulsory to contact a professional mechanic when your vehicle engine starts rough idle.

Read More: Why Car Shakes at Idle

3) Poor Acceleration

A defective knock sensor can cause the engine to experience poor acceleration while driving on the highway. The powertrain control module (PCM) uses the data of the knock sensor to adjust the ignition timing and air-fuel mixture.

When the knock sensor becomes faulty, it sends wrong or no signals to the PCM. When the PCM receives wrong information, it may be unsuitable adjustments to the fuel mixture and ignition timing, which cause the engine to lose power and result in poor acceleration.

4) Pinging Sound from the Engine

When the knock sensor goes bad, the Powertrain Control Module (PCM) might be unable to detect or correct spark knock. This malfunction may lead to a metallic pinging sound coming from the engine compartment, which may become more noticeable when your engine is under significant load.

5) Poor Engine Performance

A faulty knock sensor may force the PCM to incorrectly adjust the air-fuel mixture and ignition timing, which may lead to poor engine performance. You may experience issues while driving at high speeds or when the car lights are turned on the light. In such situations, it is advisable to consult a mechanic for an inspection, even if the check engine light has not been triggered.

6) Poor Fuel Economy

Whenever your engine operates using default values, its performance is not optimized. This affects not only power and acceleration but also fuel economy.

However, when the knock sensor goes bad, the decrease in fuel economy might not be drastic; you may notice a reduction of a few miles per gallon.

7) Reduced Engine Power

A reduction in the engine power is a clear symptom of a bad knock sensor.

The faulty knock sensors can impact not only the vehicle’s acceleration capabilities but also its maximum torque and speed. This is because the engine’s control system returns to default values to prevent excessive force production, which could cause further damage. By reducing the force, the vehicle’s PCM simultaneously lowers the power output.

Causes of a Bad Knock Sensor

Following some factors may lead to the failure of a bad knock sensor:

Age and normal wear
Wrong installation of the sensor
Corrosion
Physical damage
Disconnected, frayed, or damaged wires connected to the knock sensor
Manufacturing faults
Faulty parts of the sensor
Coolant or oil leakage onto the knock sensor
Use of dirty or low-quality fuel
Faulty spark plug
Carbon accumulation within the engine cylinder

What Is a Knock Sensor?

A knock sensor is a mechanical device installed in an engine that is used to monitor abnormal combustion events known as “detonation” or “knocking.”

It is an accelerometer or piezoelectric-based sensor that produces a voltage signal when it monitors engine vibration because of these unusual combustion events.

The knock sensor of your vehicle transfers its data to the powertrain control module (PCM). The PCM utilizes the data of the knock sensor to adjust the air-fuel mixture, ignition timing, and some other features.

When the PCM monitors the engine knocking, it immediately makes a change in the ignition timing or air-fuel mixture to minimize or remove the detonation. By doing this, this sensor assists the vehicle’s computer to optimize fuel economy, preventing the engine from damage, and improving engine performance.

Knock sensors are most usually used in the latest petrol engine vehicles, particularly forced induction systems (i.e., turbochargers) or those with high compression ratios.

What is a Knock?

Engine knock, also known as detonation or pinging, is an undesirable noise that is produced in an internal combustion engine when an abnormal combustion event occurs within a cylinder that is separate from the intended, controlled ignition initiated by the spark plugs.

For engine knock to happen, several conditions must be met. First, the spark plug ignites the air-fuel mixture, creating a flame front that moves by the remaining space within the engine cylinder. As the flame front moves, it pressurizes the remaining air-fuel mixture. This increase in pressure leads to a rise in temperature.

In certain situations, the temperature can become so high that it causes a second, unintended ignition event. This second ignition produces another flame front, and when those two flame fronts hit each other, an engine knock occurs.

Knock Sensor Location

The location of the knock sensor varies according to the vehicle’s make and model. The knock sensor is most commonly located in the intake manifold, the cylinder head, or the engine block.

It is also connected to the engine block. Your knock sensor should be installed in such a way that it can easily detect vibrations and sounds within the engine.

Due to the varying locations of knock sensors, it is advisable to know what to look for before beginning your search. A helpful approach is to look up your vehicle’s specific knock sensor on a parts website to identify its appearance and location.

If you’re uncertain whether you’ve located the right sensor, it’s best to consult a professional technician for repairs to avoid inadvertently causing further damage to your vehicle.

How do you replace a knock sensor?

Follow the following steps to replace a knock sensor:

Turn off the engine
Open the vehicle’s hood and allow the engine to cool down because a hot engine may damage your skin while working on it.
Remove the negative terminal of the battery.
Find your sensor, which is usually attached to the engine block near the intake manifold. Keep your new sensor nearby for comparison purposes when locating the old one.
Use common mechanic tools to remove the nuts and bolts.
Disconnect the wiring harness from the sensor.
Install the new sensor and secure the wiring harness connections.
Insert the retaining bolt back into the sensor’s mounting hole and tighten it using an adjustable wrench in a clockwise direction.
Reconnect the negative terminal of the battery.
Turn on the ignition switch and perform a test drive.

Knock Sensor Replacement Cost

The replacement or repair cost of the knock sensor varies according to the vehicle engine, model, your living location, and labor cost.

The average replacement of a knock sensor is from $115 to $730. In this cost, the sensor itself cost is between $40 and $80, while the labor cost is between $75 and $650.

FAQ Section

What is the function of Knock Sensor?

The main function of the knock sensor is to monitor abnormal combustion events known as knocking within the engine. The Powertrain control module (PCM) utilizes the sensor data to adjust engine timing and air-fuel mixture.

Can a bad knock sensor cause rough idle?

Yes, a faulty knock sensor may lead to a rough idle. When the knock sensor becomes faulty, PCM doesn’t get correct information about unusual combustion events happening within the engine. As a result, the PCM doesn’t properly adjust the air-fuel mixture or ignition timing, leading to a rough or unstable idle.

Does a bad knock sensor cause a check engine light?

Yes, bad gas may trigger the check engine light or a knock sensor code. Contaminants or poor-quality fuel with a low octane rating usually leads to knocking, which may trigger the check engine light and result in a related trouble code being stored in the powertrain control module (PCM).

Can a faulty knock sensor damage the engine?

A malfunctioning knock sensor can harm the engine if left unattended. Signs of a bad knock sensor include poor compression readings, high emissions, reduced power, and performance, or knocking sounds. If you notice any of these issues, it’s important to replace your sensor promptly.

Can I drive with a bad knock sensor?

Yes, it is possible to drive with a faulty knock sensor, but it is not advisable. Driving with faulty knock sensors may produce different drivability issues, such as diminished performance, increased emissions, and reduced power. It is advisable to address the problem and replace the sensor before engaging in extensive driving.

What happens when a knock sensor goes bad?

When the knock sensor goes bad, it sends the wrong data to the PCM. When PCM receives wrong data, it doesn’t properly adjust the engine timing and produces different drivability issues such as engine knocking, poor acceleration, reduced engine power, or poor fuel economy.

Can Poor quality Fuel damage the Knock Sensor?

Poor quality fuel itself can’t directly damage your knock sensor. But it may lead to poor combustion and engine knocking, which may force the knock sensor to work overtime to compensate. Over time, this extra stress may possibly lead to the failure of the sensor.

Can my car start with a bad knock sensor?

Yes, your car will be able to start with a bad knock sensor. A bad knock sensor can’t prevent your car from starting. Its main function is to monitor the engine knock and send this information to the PCM/ECM.