Bad Knock Sensor Symptoms (+ Replacement Cost)

Do you want to know the various bad knock sensor symptoms so as to know when you need a replacement? If so, then you are in the right place.

Many sensors which perform different functions can be found in your vehicle. The knock sensor is an important sensor that protects your engine, but it’s not so popular.

The question now is, what are the functions of the knock sensor? What are the bad knock sensor symptoms? And very importantly, what is the average cost of replacement? You will find the answers to these questions and more as you read on. We will start with the common signs you have to pay attention to.

One of the common signs of a faulty knock sensor will be the dashboard display of a check engine light. In severe cases, it could also lead to a detonating and knocking engine, but you will most frequently experience increased fuel consumption and engine power loss.

The five most common signs of a faulty knock sensor will be discussed below.

1. Check Engine Light

An illuminated check engine light is one of the bad knock sensor symptoms. When your check engine light pops up on your dashboard due to the knock sensor, it does not necessarily mean something is wrong with your sensor, but in most cases, it may be faulty. It could also mean that your car has a knocked engine.

Either way, a check engine light will illuminate. After reading the error codes, there may be a need to narrow the problem down.

2. Knocking Engine

your engine knocking is one of the bad knock sensor symptoms that no one wants to experience.

In most cases, even when your vehicle engine control module works without a knock sensor, it could cause pinging or engine knock. Engine knock and pinging could be detrimental to your engine and create severe damage within seconds. You should avoid it at all costs.

3. Decreased Acceleration

Decreased acceleration is one of the bad knock sensor symptoms you should look out for. You will notice an acceleration decrease immediately after the knock sensor gets bad.

This is more like an engine’s default action to prevent further damage by reducing the output. It not only reduces the possibility of additional damages but also decreases overall emissions in line with the standards of EPA.

4. Reduced Engine Power

A bad knock sensor does not only affect your vehicle’s acceleration; it also affects the vehicle’s torque and top speed. These default values make your engine revert, thereby reducing the engine’s performance and preventing more force production, which could cause further damage.

The engine’s computer will also reduce the rate of power produced by your engine due to the reduction in the level of force.

5. Low Fuel Economy

The performance level will be reduced whenever your engine goes into default mode. This does not only affect acceleration and power; it also affects the fuel economy. The reduction in fuel economy is not so obvious, but you will eventually see a decline in a few miles per gallon.

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What Causes a Knock Sensor to Malfunction?

Various factors could be responsible for a faulty knock sensor, and they include:

• Knocking or detonation due to high engine temperatures, an extremely rich fuel/air mixture, or other issues.
• Worn cylinder walls, valves, or piston rings lead to increased pressure in your cylinder, leading to knocking or pre-ignition.
• Failing spark plugs create volatile combustion and intensified pressure in your cylinders resulting in knocking or pre-ignition.

What Is a Knock Sensor, and What Does It Do?

Abnormal combustion in the engine referred to as a spark knock can be detected by a knock sensor using an internal piezoelectric component. Detonation or spark knock is an unpleasant happening that creates an unusual cylinder pressure increase, which often results in a metallic pinging sound from your engine.

Some common factors of a spark knock are the build-up of carbon in your engine’s combustion chambers, low octane gas, extremely advanced ignition time, and unusually high engine temperatures.

If ignored, spark knock could lead to an expensive internal engine deterioration. This is why almost all modern cars have at least 1 knock sensor that helps Monitor the engine for signs of a spark knock.

An alternating current signal is created by the knock sensor and sent to your engine’s computer, and it is commonly known as a Power Control Module. When the power control module detects signs of a spark knock, the ignition timing will be delayed by the module till the knock goes off.

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How to Test a Knock Sensor

Before getting a new knock sensor, you should test your current knock sensor. You will need to get the car’s repair information before commencing.

Getting manuals, especially from Chilton, is good, but an even better option is subscribing to a database for repairs (for example, Mitchel 1 DIY or ALLDATA). You can go through our write-up on repair manuals for more detailed information about repairs.

Note: These are general procedures for entertainment and education purposes only. Adhere to your car’s manufacturer recommendations for approved safety procedures and specified repair instructions.

Step 1: Check for Diagnostic Trouble Codes (DTCs)

Checking for diagnostic trouble codes should be the first option so that the troubleshooting process will be narrowed down.

Vehicles manufactured with on-board diagnostics II after 1996 often develop a code if the knock sensor and its circuit have an issue. Most older vehicles with on-board diagnostic equally store a code whenever the knock sensor has an issue.

Diagnostic trouble codes can be checked using a code reader or a scan tool. Nowadays, a less affordable on-board diagnostic II code reader can be on your smartphone.

However, it is important to note that the diagnostic trouble codes barely spot the exact vehicle issue. These codes only serve as a guide for further investigation.

Step 2: Perform a Visual Inspection

The next step will be carrying out a visual examination. You could inspect for problems such as poor connections and damaged wires. Ensure that the electrical connector of the knock sensor is tight and clean. Fix every problem identified during the inspection, erase the diagnostic trouble codes and observe if the issues reappear.

Step 3: Test the Knock Sensor Directly

It can be a little tricky to test the knock sensor. The knock sensors are primarily of 2 types: resonance piezoelectric and wideband piezoelectric.

The wideband piezoelectric sensor takes up vibrations within the entire frequency range. Meanwhile, the resonance sensor picks up vibrations only within the spark plug frequency range.

Because of this, the resonance sensors are often known as “tuned” knock sensors because they are often tuned to the same frequency range as the spark knock ( somewhere around 5,000 & 9,000 Hz).

Previously, when the wide band piezoelectric sensor was common, the test method commonly used was tapping on the engine close to the knock sensor. When the sensor responds to these vibrations, you will know its functioning to some extent.

But this test is not effective on the recent resonance sensors. Many experts use alternative methods for testing these sensors, such as compelling the engine to exhibit spark knock or ping while observing the sensor’s output signal.

Knock Sensor Location

The knock sensor has various possible locations, but it can be found in the intake manifold, cylinder head, and engine block. The most regular is having it fastened to the engine block. Note that the knock sensors have to feel and hear what is happening.

Due to the various locations of a knock sensor, it is better to understand what you want before starting fully. You can easily do this by considering the specific parts before purchasing yours.

Also, remember that since they are electrical connectors, if it’s falling out of the sensors back, you will be able to know if you look in the appropriate area. However, be sure to disconnect the correct sensor since many sensors exist.

If you are unsure you picked the correct sensor, do well to visit your mechanic so that you will not create more damage leading to more expensive repairs.

Knock Sensor Replacement Cost

Replacing a knock sensor will cost about $250 to $350 on average, depending on your car’s model and the automobile shop you contacted. Also, remember that this amount applies to a faulty knock sensor only and not for a knocked engine.

Before any replacement is done, ensure to carry out a proper diagnosis. With that, you can stop the error of replacing the wrong part and wasting money.

You can also do the repairs by yourself, that way you’ll be able to save some money.

Depending on your vehicle’s model, a thrift knock sensor is about $20-$100. Note that OEM components will be more expensive, but if your car is under warranty, you will need an OEM part.

However, if a mechanic does the repairs, the average labor cost for replacing the knock sensor will be between $150 and $250.

The difference in the labor cost depends on your vehicle model. In most vehicles, locating the knock sensor can be a bit challenging; you may have to take some components off. If the components removed are more or too complicated, the labor cost will be higher.

This means you will have to engage the services of an expert. But it will be an added advantage if you can effortlessly do the job by yourself.

Can I Drive With a Bad Knock Sensor?

Technically, driving with a faulty knock sensor is possible, but this also relies on the rate your motor will be dependent on, lots of fuel will be burned, or you will not drive for long.

You must get a faulty knock sensor replaced immediately you notice it. It is risky to drive with a bad knock sensor. In most cases, your engine may suffer severe damage, and you won’t be able to discover it sooner, and you will be left with a damaged vehicle.

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How to Replace Knock Sensor

You can dedicate 1 or 2 hours of your time to getting the replacement of the faulty sensor done if you possess the basic mechanical skill or experience. YouTube could also be of great help.

The first step is to use your smartphone and capture as many pictures as possible so that you will know the position of everything, making coupling easy. Ensure the battery is disconnected. g

Get other brackets, wires, and hoses out of the way. You will appreciate it later.

Get the new sensor and try locating the broken one. This may sound unimportant, but you must locate the right sensor. Picking the wrong point will only result in a waste of time, money, and energy.

After replacing the sensor correctly, use the pictures you captured earlier as a reference and put the components back in their correct position. You can now reconnect your battery and ignite your vehicle to check if the CEL has disappeared.

Frequently Asked Questions – Bad Knock Sensor Symptoms

Conclusion – Bad Knock Sensor Symptoms

Various problems could be created as a result of a faulty sensor. The common ones include rough idle, low power, high CO and HC levels in your exhaust, and failed emission testing. If you observe any of these symptoms, ensure to get the knock sensors replaced.

Many vehicles with a distributor-less or electronic ignition enable easy replacement, but vehicles with a distributor ignition may face some difficulties. Ensure to remove the knock sensor’s wiring harness before you remove or replace it.

If your vehicle has higher levels of CO and HC, failed emissions testing, and is running poorly, then your car has a faulty knock sensor. If you cannot check it yourself, ensure to consult an expert.