There are many sensors in every automotive engine used for regulating things like temperature, emissions, and ignition timing. One of these sensors is known as the ‘Knock sensor.’
The term Knock can be ascribed to detonation, pinging, spark knock, or pinking. The knock sensors are usually located on the intake manifold, head cylinder, or engine block.
It is a listening device that enables your car computer to detect noise and vibrations caused by engine knock.
If your engine longevity is important to you, you want to listen to vibrations and knocking happening inside your engine. Hence, you should be able to identify symptoms of a bad knock sensor.
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 Does A Knock Sensor Do?
The knock sensor’s job is to measure knocks in the engine and generate a voltage signal sent to the ECU, from which the ECU will receive and analyze this signal to adjust the ignition advance angle to reduce knocking (usually, the knock is caused by the mechanical parts of the engine being detonated).
In the event of a fault, the ignition angle is the most recent. If an explosion is detected, the ECU will reduce the ignition angle prematurely.
When the engine is running for some reason, causing knocking (self-ignition, engine overheating, mechanical shock, etc.), the sensor will generate a voltage signal and send it to the ECU, and the ECU will automatically adjust to reduce the noise.
Specifically, the piezoelectric element of the knock sensor is designed with the size of the natural frequency coinciding with the motor’s oscillation frequency when the detonation phenomenon occurs, so that the resonance effect occurs (f = 6KHz – 13KHz).
Thus, during engine detonation, the quartz crystal will be under maximum pressure and will generate voltage.
This voltage signal has a value of less than 2.5V. Using this signal, the engine ECU detects detonation and reduces the ignition angle until no more detonation. The engine ECU can adjust the re-ignition timing.
Knock Sensor Location
There are a few different possible locations for the knock sensor, but the most common places include the engine block, the cylinder head, or the intake manifold.
The most common is that it is bolted to the engine block. Keep in mind that your knock sensor needs to hear and feel what’s going on.
Because of the wide variance in a knock sensor’s locations, it’s best to have an idea of what you’re looking for before you start. A good way to do this is to look up your vehicle’s specific knock sensor on a parts site before trying to track yours down.
Finally, keep in mind that these are electrical connectors, so you’ll be able to tell if you’re looking in the right area if there’s an electrical connector sticking out of the back of the sensor.
However, there are tons of different sensors, so make sure you’re disconnecting the right one.
If you’re not sure if you’ve found the right sensor, consider taking your vehicle to a certified mechanic for repairs so you don’t accidentally cause further damage.
Symptoms of a bad knock sensor
A lousy knock sensor can cause severe engine damage if not detected and replace on time. So, if you notice any of the following signs, you want to seek professional advice.
#1. Check Engine Light.
One of the first symptoms that will indicate a lousy knock sensor when giving concern about your engine’s healthiness is the check engine light popping up on your dashboard. You might see this light on your dashboard.
However, several factors could cause the check light to display on your dash. One of these reasons is a faulty knock sensor.
Other reasons why the engine warning light may display on your dash depend on the fault your vehicle engine is encountering.
One of these reasons is a bad O2 sensor, which monitors the amount of unburnt 02 in the exhaust system, regulates the fuel-air mixture that enters the cylinder walls, and reports data to the car computer.
Another reason this light might come up beside the lousy 02 sensor and faulty knock sensor is a loose gas cap, which helps prevent fumes from escaping.
In addition to these causes, a clogged catalyst converter in your exhaust system turns carbon monoxide into carbon dioxide and can be the reason behind the warning light.
The engine warning light is generally the first visual and noticeable symptom of a bad knock sensor Honda Accord or any other car make and model. In all, a lousy knock sensor can damage your entire engine if ignored.
#2. Loud Sound.
When the knock sensor starts malfunctioning and eventually goes wholly bad, you will hear a bad knock sensor sound. What sound does a bad knock sensor give? A lousy knock sensor will deploy a loud thumping sound in your engine.
The longer you drive without solving the cause of the sound, the louder the sound becomes. These sounds occur within the cylinder walls due to the timing of the ignition of the air-fuel mixture.
#3. Poor Acceleration.
If the knock sensor goes faulty, it’ll no longer aid the ECU resulting in low engine performance. Therefore, the car will suffer from poor acceleration.
Because the Pressure generated in the combustion chamber is just a part of an engine capacity, the torque is lower, and your car will have acceleration issues. Poor acceleration is a common symptom of bad knock sensor Hyundai.
#4. Low Gas mileage.
Many factors can cause reduced gas mileage; however, if you notice reduced gas mileage in addition to any of the outlined signs in this article, you should have a professional inspect your knock sensor.
The knock sensor might have to blame. When the ignition timing is insufficient, it can cause unnecessary knock or ignition resulting in lower gas mileage.
#5. Reduced Engine Performance.
The most noticeable symptoms of bad knock sensor Ford that you will notice might be when your internal engine components damage or break down over time.
If you have seen the symptoms of bad knock sensor 5.3 and ignore it, shortly, you will start experiencing poor acceleration, misfiring, jerking, and drags. In some cases, you might begin perceiving a burning smell.
The smell may be strong enough that both the passengers and driver will notice it. If you continue driving your vehicle in the state, you might damage your entire engine, and you’ll need to replace it.
The engine of a car is one of the most expensive parts you can find in any vehicle regardless of the make, model, and vehicle year. Replacing an engine sometimes can be higher than the vehicle’s overall worth.
On average, the cost of a new engine would be $2,000 – $4,000 for a four-cylinder engine.
The price can go above $4,000 if your car has a V-type engine. The actual price solely depends on the car make, model, year, and the dealership you want to get the engine.
Causes of a Bad Knock Sensor
A knock sensor can fail due to internal faults in the sensor itself or problems with the wiring that connects the sensor to the ECU.
These issues can come from a variety of sources. If you don’t address the underlying cause of the bad knock sensor, any replacement sensor could just as easily fail again in the future. Here are the top five reasons:
- A Short Circuited Wire
- Corrosion From Weather Exposure
- A Hot-Running Engine
- Carbon Buildup & Engine Vibrations
- Accidental Physical Damage
#1. A Short-Circuited Wire is a serious issue.
The shielded wiring running from the knock sensor to the car’s ECU is exposed to a lot of heat or other wear and tear.
Over time it’s possible for the protective coating to degrade causing a short, which can burn out the somewhat delicate piezoelectric element within the knock sensor.
#2. Corrosion From Weather Exposure.
A bad knock sensor can also be caused by exposure to the elements. The most common is water that gets into the engine bay. This might be from driving through a deep puddle or strong winds in a rainstorm that let water get into the engine bay.
This can cause corrosion on the metal elements of the piezoelectric element. Though corrosion on the connection between the shielded wire running to the car’s ECU could also develop from weather exposure.
#3. A Hot Running Engine.
Knock sensors are mounted on or very near the engine block, which exposes them to a lot of heat. This can cause a failure in the wiring or lead to metal fatigue that fractures the piezoelectric element inside the knock sensor house.
In a case like this, the car might have overheated badly a few times, and even after the overheating issue is fixed, the knock sensor still fails on its own.
#4. Look for Carbon Buildup And Engine Vibrations.
Carbon buildup in the cylinders can lead to spark knock and other severe engine vibrations which can damage a knock sensor. In a scenario like this, you’ll likely notice the engine knocking from time to time.
The ECU might even be able to compensate for the spark knock at first. Though the recurring vibrations can damage the somewhat delicate components within the knock sensor.
#5. Accidental Physical Damage.
Most knock sensors are mounted to the engine block or the intake manifold and can get in the way when you’re working on something else in the engine bay.
All it takes is a dropped tool or an accidental bang to damage the knock sensor housing, deform the piezoelectric element or damage the shielded wire running to the ECU.
How to Test a Knock Sensor?
It’s a good idea to test a suspect knock sensor before you rush out and buy a new one. Before getting started, however, you’ll want to have the vehicle’s repair information handy.
Manuals, such as those from Chilton, are good, but a subscription to a repair database (e.g., ALLDATA or Mitchel 1 DIY) is even better. You can find more information on accessing quality repair information in our article on repair manuals.
Note: The following are general guidelines for educational and entertainment purposes only. Consult your vehicle’s factory information for specific repair instructions and recommended safety procedures.
Step 1: Check For Diagnostic Trouble Codes (DTCs).
The first thing you’ll want to do is check for DTCs that could narrow down the troubleshooting process. Cars built after 1996 with on-board diagnostics (OBD) II will usually set a code when there’s an issue with the knock sensor or its circuit.
Some older cars with OBD I will also store a code when there’s a problem with the knock sensor. Faulty parts like bad spark plugs can cause a knock sensor code, so you’ll need to inspect your vehicle thoroughly if it sets a DTC.
You can check for diagnostic trouble codes using a scan tool or code reader. These days, you can even get an inexpensive OBD II code reader for your smartphone.
It’s important to point out, however, that DTCs do not tell you the exact problem with the car. Codes merely serve as a starting point for further diagnostics.
Step 2: Perform a Visual Inspection.
Next, you can move on to performing a visual inspection. You’ll want to look for issues, such as damaged wires and poor connections. Make sure that the knock sensor’s electrical connector is clean and tight.
Repair any issues found during the visual inspection, clear the DTCs, and see whether the problem returns.
Step 3: Test the Knock Sensor Directly.
Testing a knock sensor can be tricky. There are two primary types of knock sensors: wideband piezoelectric and resonance piezoelectric.
Wideband piezoelectric sensors pick up vibrations within an entire range of frequencies. On the other hand, resonance piezoelectric sensors only respond to vibrations that are within the same frequency range as spark knock.
For this reason, resonance sensors are sometimes referred to as “tuned” knock sensors because they’re tuned into the same frequency range as spark knock (typically, somewhere between 5,000 and 9,000 Hz).
In the past, when wideband piezoelectric sensors were more common, a popular test method was to tap on the engine near the knock sensor. If the sensor responded to the vibrations, you knew it was working to some degree.
But that test does not work on the newer, resonance-style sensors. Most professionals test these sensors using an alternate method, which involves forcing the engine to ping (exhibit spark knock) while monitoring the sensor’s output signal.
Cost of Knock Sensor Replacement
A knock sensor can assist in improving fuel efficiency and torque, giving the vehicle additional power. It is a crucial engine component in terms of performance.
When this component breaks, drivers may notice a reduction in power or mileage, as well as considerable engine head damage over time.
The average engine knock sensor replacement cost ranges from $180 to $400. A pickup truck sensor will be more expensive than a sedan sensor.
The majority of the expense is labor, while the sensor itself is just about $80. The real pricing range, however, is determined by the manufacturer and model. Here’s the total cost breakdown:
- Part cost: The knock sensor itself is usually pretty cheap. For most cars, the part will cost between $40 and $150.
- Labor cost (The Big Factor): This is what causes the price to change so dramatically. The cost is based on where the sensor is located. For example, on some engines (many 4-cylinders), the knock sensor is bolted right to the outside of the engine block. A mechanic can replace it in less than an hour. In this case, you can expect the total bill to be in the $150 to $250 range.
How To Maintain and Handle Knock Sensor Errors?
When encountering errors related to the knock sensor, some solutions can be applied as follows:
- Check connection: Check the knock sensor connection to make sure that it is connected correctly and that there is no broken wire. If there is a connection problem, remove it and plug it back in or replace it.
- Check sensor condition: Use a tester to check the condition of the knock sensor. If the sensor does not work, replace it with a new one.
- Cleaning the sensor: If the sensor is dirty or dirty, clean the sensor using a suitable cleaner.
- Repair or replace related components: If other components in the engine control system fail or do not function properly, they can cause knock sensor-related errors. Check and repair or replace these components.
- Change driving mode: If knock sensor-related failures occur due to incorrect driving mode, adjust the driving mode to ensure the safety and optimum performance of the dynamic control system muscle.
FAQs.
Q: Can a bad knock sensor cause knock?
Yes, a bad knock sensor can cause severe knocking on your engine. A few days ago, I diagnosed a Lexus LX570 model and got faulty code P0325.
Before the diagnosis, the car idles quietly, and if I engage the gears, the car will give a heavy knocking. The knocking was much that I thought something more serious is wrong. When I replace the knock sensor, the noise stops instantly.
Q: Is it easy to replace a knock sensor?
In some cars, replacing a faulty knock sensor can be pretty straightforward. You might not have to lose many things on the engine before accessing it.
However, replacing a lousy knock sensor on most newer cars can be a pain in the neck. You will have to take off several engine components before accessing them.
Q: What happens if I don’t replace my knock sensor?
A knock sensor is there on your engine to detect engine noise caused by pre-ignition. This is to enable your car computer to advance the ignition timing without allowing the engine to ping. This will give you optimum operating engine power and fuel mileage.
If the knock starts malfunctioning, the engine could begin igniting, and the car computer might not detect it.
The pinging can cause severe issues like blowing holes in the Piston or even cause the combustion process to burn. If a knock sensor goes completely bad, you’ll experience loss of fuel mileage, hesitation, and reduced power.
Q: What causes code P0325?
P0325 is an OBDII trouble code that indicates a lousy knock sensor malfunction (Bank1, sensor 1). This trouble code tells that your knock sensor is faulty and needs to be checked and replaced.
Q: What does a knock sensor do?
The knock sensor detects pre-ignition and detonation happening inside the engine block. Though, you can easily hear full-blown knocking and pinging with the help of a knock sensor.
Q: How do you install a knock sensor?
Issues with your knock sensor not be ignored because continuous pre-ignition can bow holes in the Piston and eventually destroy the pistons and the entire engine.
If you have done any minor or major work on your car successfully, you can install a knock sensor by just:
- locating the knocking sensor
- Unbolting the fastening bolt with common mechanic tools
- Unplugging the connecting wires
- Reinstalling the new one and tightening the connecting wires.
If you can’t locate the knock sensor on your car, you might want to contact a professional mechanic. Some sensors require taking off many other components before you can get to them.
Final Thought
Getting to this point means that you must have known what causes a knock sensor to go bad and the symptoms of a bad knock sensor.
So, Once you notice any of these faults, not just one of these symptoms, but two or three at once, you should seek professional advice to avoid unnecessary damage to your entire engine.