Bad Knock Sensor Symptoms: Issues, Replacement Process, And Cost

Bad Knock Sensor Symptoms: Issues, Replacement Process, And Cost

Cars have dozens of sensors that constantly measure the function and condition of the vehicle. Some measure oxygen, air, or temperature measurements, while others like knock sensors monitor vibration and noise levels, so the engine functions optimally. In this article, we will be covering all about a knock sensor including its functioning, symptoms of a bad knock sensor, and the replacement process.

Engine Knock: What Does It Mean?

Engine knock, also known as engine ping or detonation, is the noise and reaction that occurs when a second unplanned launch or explosion occurs in the cylinder, apart from the standard, controlled ignition of the spark plug. In other words, knocking is bad news for the engine. For this to occur, a few things have to happen.

Basically, the ignition of the spark plug creates a flame surface that passes through the remaining cylinder space. This movement of the flame surface pressurizes the remaining air and fuel mixture. An increase in pressure means an increase in temperature, which can be very hot and causes a second ignition. The second ignition creates a second flame surface, and when these two reactions collide, knocking occurs.

Why Does Knock Happen?

There are multiple reasons for knock to happen. The following are the main factors resulting in the same:

1. Increased Intake Temperatures

Have you ever noticed that your car slows down when it’s hot outside? The heat not only reduces the intake density but also increases the possibility of knocking. On hot days, the temperature of the combustion gas rises.

This increases the risk of combustion before the cylinder is ready to ignite the air-fuel mixture. To counter this, most engines delay ignition timing at high temperatures to make combustion safer.

2. Usage Of Low-Quality Fuel

Have you ever put fuel in a gas tank with a lower octane number than specified by the manufacturer? Octane number is the resistance of a fuel to an explosion due to compression. The higher the octane number, the more resistant it is to compression ignition.

bad knock sensor symptoms

Using the wrong fuel can cause the engine to knock. Please note that some vehicles are designed to operate in multiple octanes. In such situations, the engine will be adjusted accordingly.

3. Carbon Buildup

As vehicles age, carbon deposits build up on valves, cylinder walls, and pistons. These carbon deposits can create hotspots that ignite the fuel unevenly.

There are ways to reduce or remove carbon deposits. Some examples are walnut blasting of valves, sea foaming, or performing catch cans. The receiver and air-oil separator (AOS) are two devices that clean the oily air mixture discharged from the positive crankcase ventilation (PCV) system.

4. Faulty ECU Calibration

The ECU may be programmed to make the engine too lean or to make the ignition timing very fast. The lean air-fuel ratio maximizes fuel economy.

Advanced timing burns the air-fuel mixture early in the combustion cycle, maximizing performance. In extreme cases, engine knocking can occur in both situations. ECUs are often factory-operated on the slimmer side for emission reasons. This is usually fine, but sometimes the manufacturer goes too far.

In this case, the manufacturer issues a recall or Technical Service Bulletin (TSB) to flush the ECU. The updated engine management software aims to allow the engine to calibrate more safely.

Knock Sensor Explained

Knock sensors are essentially small “listening” devices” in or on the engine that detect irregular vibrations and noise from the engine block. They detect vibration and noise from the engine block, convert it into an electronic signal, and send this signal to the engine control unit (ECU). The car’s computer then evaluates the information to determine if the ignition timing needs to be changed.

Knock Sensor Location

The knock sensor is usually mounted just outside the engine block, but in some cases, it is located below the intake manifold.

Components And Functioning

Your knock sensor listens for specific frequencies and is tuned for your engine. The type of engine knock that the sensor is “listening to” is measured at thousands of cycles (kHz) per second. The engineer determines the knock frequency of the engine and the window of crankshaft rotation where each cylinder explodes.

“Knock” heard by the sensor, does not match the expected frequency, or does not occur in the expected window of any cylinder is ignored. This is also reasonable in that the ECM / PCM can determine the cylinder from which the ping originated. The good news is that with a coil-on-plug engine, you can control the timing individually for each cylinder. Therefore, if only one engine performs a ping, the ignition timing for that particular cylinder can be delayed enough to stop the ping.

As far as the sensor works, the sensor produces spikes from 0 to 4.5 volts depending on the size of the knock measured. Even if the engine is running normally, there is a knock sensor working and the ECM / PCM is aware of this. If the engine is running and the knock sensor is not producing any signal, the code P0327 is set.

Differences In Difference Vehicles

Some early knock sensors receive a 2.5-volt feed from the engine controller, change when an engine knock is detected, and set the code when the voltage shorts to zero or rises to 5 volts.

Some V-engines have two knock sensors in the valley below the air intake, and in these engines, the sensors are in “wells” covered with a rubber grommet. If the grommet leaks, water will flood the sensor and destroy it. This often happens with 4.8 / 5.3 / 6.0L Chevy V8.

On some engines, the knock sensor is screwed into the side of the engine block and you may actually feel the knock through the coolant on the side of the engine cooling jacket. Do not underestimate the symptoms of a bad knock sensor as it can lead to engine damage.

Ion Sensing Knock Sensor

Another type of knock sensor is the ion sensor. This is a novel idea used in BMW, Ferrari, and other luxury cars. This method basically draws current through the spark plug and detects any type of current difference that can indicate a nonstandard explosion. This isn’t a widely used method, but it’s still very cool.

Working Of A Knock Sensor

The majority of knock sensors use piezoelectric ceramics or elements. Piezoelectric ceramics are smart materials that convert mechanical effects (pressure, movement, vibration, etc.) into electrical signals and vice versa.

Due to their electromechanical effect, piezoelectric ceramics are used in a wide range of applications. Examples include motion sensors, clocks, ultrasonic power converters, stone crushers, ultrasonic cleaning, ultrasonic welding, active vibration damper, high-frequency speaker, an actuator for nuclear microscopes, etc.

Purpose of Knock Sensor

If the cylinder is normal, it will not knock at all. However, the ultra-lean mixture used in modern engines tends to have higher combustion temperatures. Also, when the heat of combustion is transferred to the carbon deposits in the cylinder head and piston crown, some carbon can be hot enough to start the combustion process before the spark plugs ignite.

When this happens, the resulting multiple flame planes converge and hit the head of the piston as it rises, with enough force to make a “pin” sound, which means an “explosion” is occurring. takes.

Part of this reason is that as carbon begins to attach to the head and piston crowns, these layers occupy space in the combustion chamber, increasing compression and making the combustion event hotter than normal.

For the past few years, if you have tuned the distributor to adjust the ignition timing, if you make the ignition timing too early, the ignition will actually occur before the ignition timing occurs and the combustion event will “sound”, so “knock”. The same thing happens, except that it is called. To the head of the piston as it rises.

Fuels with an octane number lower than the vehicle’s rating can also cause an explosion due to the burning rate of the fuel. Using 87 octane gas with an engine that is compatible with 93 octane gas will usually explode under load. Cold trips can also occur when using 93 octane gasoline in a vehicle tuned to 87 octane.

Knock Sensor Code

There are multiple OBD trouble codes associated with the functioning of a knock sensor. Let’s look into the most common ones among them.

Knock Sensor Diagnostic trouble code (DTC) P0325

Diagnostic trouble code (DTC) P0325 is an abbreviation for knock sensor malfunction (sensor 1, bank 1). This code indicates that the car’s primary computer often referred to as the powertrain control module (PCM), is detecting a problem with the sensor or its circuit.

The knock sensor detects the vibration of abnormal combustion called spark knock. Your car may have one or two knock sensors, depending on the make and model.

Knock Sensor Diagnostic Trouble Code P0330

Diagnostic Trouble Code (DTC) P0330 is an abbreviation for “Knock Sensor 2 Circuit (Bank 2)”. Indicates that an error has been detected in knock sensor 2 or its circuit.

The P0330 code is stored in the vehicle’s memory when the PCM detects that the input voltage from knock sensor 2 is too high or too low. If left uncorrected, this trouble code can lead to more serious engine problems and damage.

After pinpointing the root cause, investigate on forums and other similar platforms to find a repair that worked to clear the P0330 code. Ideally, you should stick to the information shared by people who own the same vehicle.

Knock Sensor Diagnostic Trouble Code P0326

Diagnostic Trouble Code (DTC) P0326 is an abbreviation for “Knock Sensor 1 Circuit Range / Performance Bank 1”. Set when the powertrain control module (PCM) detects that the signal from the knock sensor is out of the specified range. It can be logged even if the PCM does not detect the signal from the knock sensor.

Code P0326 can be set in motors of various makes and models. However, there’s no familiar answer for this code. All automobiles are constructed in another way and can require various solutions.

Always check with the manufacturing unit to restore records precise for your car earlier than beginning any repairs. You also can prefer to deliver your automobile to a mechanic keep if you’re nevertheless uncertain of what to do.

Knock Sensor Symptoms

There are different signs that suggest that your knock sensor is faulty or malfunctioning. The following are the most common symptoms of a bad knock sensor:

1. Check Engine Light

One of the first symptoms of a bad knock sensor you notice is the dashboard check engine light. You should take this early warning sign seriously and have your vehicle checked before the problem worsens.

Of course, there are many reasons why the check engine light should come on, but one of them is a knock sensor failure. Whatever the reason, don’t ignore it for a long time. Ignoring it can cause havoc to the engine.

2. Loud Noises From The Engine Bay

When the knock sensor starts to fail, you will hear a loud noise from the engine. This is like a loud noise. The longer you do not fix this problem, the greater these noises will be.

The reason for this noise is the ignition of the air-fuel mixture in the cylinder. Normally, the air-fuel mixture reaches the combustion point instead. Therefore, when it sounds like this, you should be immediately motivated to take the vehicle to a mechanic.

3. Low Fuel Economy

If you notice that you’re traveling lesser miles per gallon than usual, it could be due to a defective knock sensor. Again, there are many reasons for poor fuel economy.

bad knock sensor symptoms

But if you notice any of these other ‘bad knock sensor symptoms’ associated with poor fuel economy, that’s even more reason to attribute it to a bad knock sensor.

4. Poor Acceleration

If the knock sensor is out of order, it will not help the control unit and will reduce engine performance. Therefore, the acceleration of the car becomes worse. The pressure generated in the combustion chamber is only part of the engine output, resulting in lower torque and problems accelerating the car.

5. Rough Idling And Engine Backfiring

This is an evident symptom that you will surely feel. It feels like the engine is going to seize up or stop running completely. It is not something you want to take lightly.

6. Catalyst Damage

Poor knock sensors can damage a car’s catalytic converter, increase HC (hydrocarbon) emissions, and further reduce MPG emissions. Hydrocarbons from misfired or malfunctioning engines are released into the atmosphere without burning completely.  It is a big problem for our environment, and if it is done too long, it will lead to catalyst failure.

7. Underwhelming Engine Performance

The worst symptom of a knock sensor failure occurs when components inside the engine are damaged. If you escalate this issue without replacing the failed sensor, the vehicle will increasingly start dragging and jerking.

There may even be a burning odor emanating from the engine and entering the cabin of the car. Further use of the vehicle in this condition can destroy the entire engine. Then you’re looking at thousands of dollars to replace the entire engine. Don’t wait for it to happen. It’s much cheaper to just replace the sensor.

Is It Safe To Drive With A Bad Knock Sensor

Technically yes, but the real question is should you do it? If the knock sensor breaks, the car will slow down. Exhaust gas production is also worsened because the engine can overheat. Overall, the performance of your car will be affected.

As mentioned earlier, if you feel that the engine is not accelerating as smoothly as before, it is possible that the knock sensor has already failed. You can prove this if driving at a certain speed feels uncomfortable, especially when towing heavy loads. When this happens, the check engine light is usually on. This is a signal you can’t miss.

In summary, you can drive with a bad knock sensor-that is, if you want to destroy the engine and get terrible performance out of the car. It is wise to replace it with a high-quality sensor as soon as you realize that the era of knock sensors has improved.

Knock Sensor Replacement

Replacing a broken knock sensor is fairly easy on some cars. You may not need to lose a lot in the engine before you can access it. However, replacing a poor knock sensor on most new cars can be a pain. Some engine components need to be removed before they can be accessed.

For most Distributor-Less Ignition (DIS) and electronic ignition cars, simply pull out the old sensor and plug in the new knock sensor.

bad knock sensor symptoms

There may be a  holding clip that holds it in place that can be removed to remove the failed sensor or bent sideways. Then use an anti-seizure agent on the new thread (if any) and screw it in with a wrench or socket until it fits snugly.

Step 1

For most distributor ignition cars, the knock sensor wire extends from the engine to the back of the car’s dashboard for diagnostic purposes, so the manufacturer can always see how badly the car is misfired.

This cable must be disconnected from the connection under the dashboard before it can be removed or replaced, and then reconnected after installation. You must disconnect the cable from the connection under the dashboard before removing or replacing the sensor. In most distributor ignition cars, two wires are connected to each knock sensor.

One carries the signal and the other carries the voltage of the sensor heating element (if any). These are usually connected together at one end of the two cables and together at the other end at the ECU (Engine Control Unit).

Step 2

Make sure it is unplugged both during installation and during subsequent plug-ins. The photo above shows an old oxygen sensor electrical connector that can be used to plug in during replacement if there is no knock sensor harness slot available under the car dashboard.

Note that on some models the knock sensors are placed side by side and only one is shown in the following image. Regardless of the number of sensors, both wires must be disconnected from the connection under the dash before removing or replacing the sensor.

Knock Sensor Replacement Cost

The cost of replacing a knock depends on several factors. The make, model, the model year of your car, and the dealer you want to bring your car with. However, the average cost of replacing a knock sensor should be between $130 and $700.

The range is very wide, with some cars using one knock sensor, some cars using two sensors, and some cars using four sensors. The average price of a knock sensor ranges from $40 to $50, but service charges range from $90 to $300.

In most cases,  parts costs and labor costs are about the same. Finding a good deal at work from an independent mechanic can potentially significantly reduce your overall cost.

Replaced Knock Sensor Still Getting Code

There are some instances when you replace a faulty knock sensor but still end up getting trouble codes. This could be because of faulty installation of the knock sensor or due to the wiring of the sensor malfunctioning. Once this happens, you should check all the components of the knock sensor, especially the wiring, and make sure everything is connected and functioning correctly.

Car Knock Sensor Function: Functional Principle – Facts

  1. The knock sensor is located outside the engine block and detects knocking noises in all engine operating states to prevent engine damage.
  2. The knock sensor converts structure-borne vibrations from the engine block into electrical voltage signals that are filtered and evaluated in the control unit.
  3. If knocking combustion occurs, the ignition signal for the respective cylinder is adjusted in the “late” direction until knocking no longer occurs.
  4. Faulty knock sensors can cause the engine warning light to come on, error codes to be stored, engine power to be reduced, and fuel consumption to increase.
  5. Faulty knock sensors can be caused by internal short circuits, breaks in the wiring, wiring short circuits, mechanical damage, incorrect mounting, or corrosion.
  6. Troubleshooting a knock sensor involves reading out the stored fault code, checking the sensor for correct fit and tightening torque, and checking the electrical connections of the sensor wiring, the plug, and the sensor for correct connection, breaks, and corrosion.
  7. Testing with a multimeter involves checking the wiring to the control unit by checking continuity and short circuit to frame for every wire to the control unit plug.
  8. The setpoint for the ohmmeter between the knock sensor connector and the removed control unit connector is less than 1 Ohm.
  9. The setpoint for checking the respective pin at the wiring harness connector against ground using an ohmmeter and with the control unit connector removed is at least 30 MOhm.
  10. If the knocking is not detected when checking with an oscilloscope, this indicates a defective sensor or circuit.


In this article, we have covered all about engine knocking and knock sensors. You’ve now learned about the position and functioning of a knock sensor and the potential issues that could affect it.

Next, the article discussed the diagnostic codes associated with a knock sensor, and the symptoms a faulty knock sensor would exhibit. Followed by this, you learned about the replacement process and cost.

FAQs On Knock Sensor And Related Issues

Here are some popular FAQs:

What Are The Symptoms Of A Bad Knock Sensor

A bad knock sensor can exhibit a number of symptoms. The most common ones among them include rough idling, engine backfiring, check engine light flashing, and bad fuel efficiency. Failing engine performance and loud noise emerging from the engine bay could also be symptoms of a faulty knock sensor.

What Is A Knock Sensor

Knock sensors are small circular devices located on most internal combustion engine blocks or intake manifolds. The bottom of the sensor is screwed into the actual block or manifold, and the top of the sensor consists of silicon donuts, piezo crystals, and electrodes.

What Does A Knock Sensor Do

The purpose of the knock sensor is to check for anomalous noise generated from the combustion chamber. When a problem is detected, the check engine light turns on and the overall engine power is reduced to protect the vehicle.

What Causes A Knock Sensor To Go Bad

A lot of factors could result in a faulty knock sensor. The main ones of those include high intake temperatures, poor quality fuel, carbon buildup inside the engine, and bad ECU calibration.

How To Test A Knock Sensor

A common test method was to hit the engine near the sensor. If the sensor responds to vibration, you know that the sensor is working to some extent. However, this test does not work with the new resonant style sensor. Most experts test these sensors using another method of forcing the engine to ping (indicating knocking) while monitoring the sensor’s output signal.

What Happens When A Knock Sensor Goes Bad

If the knock starts to fail, the engine will start to ignite and the car’s computer may not recognize it. Ringing can cause serious problems. There is a hole in the piston or it causes the burning process to burn. If the knock sensor fails completely, you will notice reduced fuel consumption, delays, and poor performance.

Where Is The Knock Sensor Located

There are several different locations for knock sensors, but the most common locations are engine blocks, cylinder heads, or intake manifolds. Most commonly it is bolted to the engine block. Remember that the knock sensor needs to hear and feel what’s going on.

How Does A Knock Sensor Work

There are several different locations for knock sensors, but the most common locations are engine blocks, cylinder heads, or intake manifolds. Most commonly it is bolted to the engine block. Remember that the knock sensor needs to hear and feel what’s going on.

How Long Does It Take To Replace A Knock Sensor

Although it depends on the vehicle and the brand, you can likely expect 3 to 4 hours of work on the knock sensor with spark plugs and parts.

How To Replace A Knock Sensor

To tighten the set screw lock on the sensor hole fixture, lift the wrench in the correct direction in conjunction with the set screw lock. Then slide the wire harness back in until the sensor is locked. Remove any other components or brackets that are not used to access the sensor.

Can I Drive With A Bad Knock Sensor

If you want to minimize engine damage, it is not advised to drive with symptoms of a bad knock sensor. As the wear progresses, it could cause serious issues. It is important to replace the sensor as soon as possible.

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