A knock sensor is a device installed in your vehicle that senses the knocking of the engine. The term knocking is also referred to as pinging, spark knock, detonation or pinking.
Typically, when the knock sensor of your vehicle goes bad it can affect the efficiency of the engine and the performance of the vehicle by not being able to manage the knocking effectively.
The knock sensor of your vehicle can fail for various reasons. In most cases, the sensor may become defective as the vehicle ages and may need to be replaced. Over time, the sensor may wear and tear. It is also susceptible to corrosion and the functionality of the sensor can be affected.
In other cases, physical damage or contact with water may cause it to become faulty. Sometimes it is only the electrical wires that cause the problem, which may be damaged or broken.
Signs of a Bad Knock Sensor
The knock sensor is a sensitive device that draws a lot of heat from the engine. The sensors are usually placed away from extreme heat, but this is one of the unfortunate sensors that sits near the engine. Therefore, this sensor can wear out over time and deteriorate through constant use.
It is therefore advisable to know the common signs of knock sensor failure.
1. Loss in Engine Performance
The PCM uses the data sent by the knock sensor to change the ignition timing, which can have a direct effect on acceleration. Sometimes you may feel that your car does not respond to the throttle because the knock sensor sends incorrect information to the PCM. Not only that, but your car also uses a lot of fuel, which makes fuel consumption worse.
If you ever feel the need to fill up with gas more often than usual, it is time to visit the mechanic to have the knock sensor checked for faults.
2. Check Engine Light Illuminates
Whenever there is something wrong with the engine, the control unit sends an error code indicating where the problem is. The same happens if the knock sensor is defective. The Check Engine Light in your dashboard will light up. The only way to detect the problem is to connect a code reader to the car.
If the knock sensor has problems, you will inevitably see an error code P0325-P0332. In this case, you should think about contacting the mechanic to find a solution. When your check engine light appears on the instrument panel, check the error codes with an OBD2 Code Scanner.
3. Misfiring Engine
If a knock sensor does not operate according to the standard, the PCM does not receive important data or receives incorrect data from the sensor. This causes the PCM to set the ignition timing incorrectly. The engine misfires and becomes susceptible to hiccups. The engine could stall or show uneven combustion.
4. Spark Plugs Go Bad
If there is more fuel than usual in the cylinder and the ignition timing is constantly changing, the spark plugs in the cylinder are overloaded, which leads to their failure. If you need to replace spark plugs prematurely, this could indicate that the knock sensor has failed or is about to fail.
What is a Knock Sensor?
The knocking occurs in the spark ignition of international combustion engines. It is caused when the spark plug flame ignition is not responsible for the combustion of the fuel in the cylinder and the fuel mixed with air explodes outside the combustion front.
In such a case, the knocking sensor senses the knocking and generates a signal from the detonation vibrations. This signal is read from the detonation vibrations by generating a voltage, and transmitted to the computer system. The computer then evaluates the signal transmitted by the knock sensor to slow down the timing.
Cleaning the Knock Sensor Connector
The plug of the knock sensor is exposed to pollutants such as dust and deposits in the engine compartment. In some cars, you may have several knock sensors. To make matters worse, the sensor also absorbs a lot of heat from the engine, so it will fail sooner rather than later.
By checking for corrosion in the connector or on the sensor itself, you may not need to replace the sensor. However, you can extend the life of the sensor by treating it with special care. Remember that this method will not help you if the sensor has failed internally.
Things you will need:
- A screwdriver
- Contact Cleaner
Removing the Sensor
The knock sensor is located inside the engine near the cylinders or the intake manifold, which means it will not be very easy to find. You will probably have to remove the upper part of the engine, also called the head, and go even further to find the sensor.
It would be better to use the services of a mechanic for this, but if you are interested, you can watch YouTube videos that will help you disassemble the engine. Once you have the sensor, it’s time to clean it.
Using Cleaner to Rub Dirt off the Connector and Sensor
The sensor plug can be cleaned in two ways: by using alcohol as a cleaning agent or by using a special sensor cleaner. The cleaning part is simple but requires additional care. The sensor can either be put into the plastic bag and rubbed with alcohol or cleaned with the cleaning agent.
In both cases, the result will be pretty much the same. Once you are done with the cleaning part, let the sensor dry for a good half hour before replacing it in the engine. Also, check if the wiring of the knock sensor is damaged.
Reinstalling the Sensor
Replace the sensor in its prescribed place and reassemble the engine. Once you have finished, start the engine and listen for any audible noise coming from the engine except for the rumbling of the engine itself.
Testing the Sensor
The knock sensor can be tested for failure in two ways. You can either use an error code scanner or test the efficiency of the sensor with a voltmeter. Both methods have their own advantages and disadvantages.
Starting with the error code scanner: it is clear that the error code scanner is the easiest way to find out any problem with the knock sensor. All you need is an inexpensive and functional OBD2 scanner that can read and display codes directly on its screen, preferably with a pre-installed code dictionary. As soon as you attach the scanner to your car, it will tell you the reason for the unpleasant behavior of your car.
A voltmeter may prove useful, but due to the location of the knock sensor, it is almost impossible to test the efficiency of the sensor with a voltmeter.
How to repair/replace the knock sensor?
You can repair or replace your vehicle’s knock sensor yourself by following an easy-to-follow step-by-step guide. It is strongly recommended that you carry a service manual for your vehicle with you before you start.
Usually, when we confirm that the vehicle’s knock sensor is defective, the best way to have it repaired is to replace it. Here’s an easy way to replace the knock sensor.
• Remove the engine from the vehicle
• Remove the intake manifold and throttle body assembly
• Locate the knock sensor on your vehicle by going through the service manual
• Make sure that you have not mistaken the knock sensor with the temperature sensor
• Clear access to the sensor
• Remove the electrical connector from the sensor
• Remove the bolts and screws that hold the sensor on the block
• Make sure you do not break the sensor while removing the tightly installed threaded screws
• Pull out the old sensor once it is unmounted
• Match the old sensor with the new one
• Install the new sensor at the proper location
• Tighten back again to as much as 29 ft. lbs
• Reconnect the sensor back to the connectors
• Reinstall the intake manifold and throttle body assembly
• Install the engine back to the vehicle if it was detached
How to diagnose a bad or failing knock sensor?
The diagnostic procedure for the faulty knock sensor requires that you physically test the sensor using an ohmmeter. The following describes how you can test the knock sensor to determine if it is faulty.
• Remove the engine from the vehicle (if necessary)
• Remove the throttle body assembly and the intake manifold
• Remove the connectors from the knock sensor
• Remove the sensor from the engine by unmounting it
• Take a multimeter or an ohmmeter and connect it with the sensor
• Check for the continuity between the terminal and the body
• If there is continuity the sensor needs a replacement
• Measure the resistance between terminals
• The resistance needs to be between 120-280 KOhms (this may vary with different vehicles, refer to the manual to make sure)
• If the resistance is not within the range, the sensor requires a replacement
Where is the knock sensor located?
The position of the knock sensor may vary depending on the vehicle you own. However, for most vehicles, there are some common locations that you can check. On many vehicles, the knock sensor is located on the block at the front behind the intake manifold.
Usually, you can attach it either to the engine block, the intake manifold, or the cylinder head. This is the most effective position for the knock sensor, as it is at these locations that it can effectively collect the necessary data regarding the vibrations caused by the detonation and knocking in the engine.
In the engine block, it is usually located on the underside. It can also easily be confused with the temperature sensor. Therefore, you must be careful when locating it and you can refer to the service manual to make sure that it is provided by the manufacturer.
Knock sensor replacement cost
The average replacement cost of the knock sensor is between $135 and $460 and the part itself costs between $85 and $110.
Once the knock sensor is defective, it is usually recommended to replace the part if everything else looks good. The knock sensor itself is not a very expensive purchase. For most vehicles, you can buy it for an average of $85 or even $110. In exceptional cases, if you have a luxury car or a special type of vehicle, the price may be higher. Nevertheless, the main cost associated with replacing the knock sensor is the cost of labor.
You can hire a mechanic or take your vehicle to a garage to have the knock sensor replaced after diagnosis. Depending on who you’re dealing with, the cost of the work can be as low as $50 or as high as $350. So on average, the total cost of the replacement, along with the labor cost, is $135 to $460.
It is also recommended that once the signs start to appear, you can have them replaced along with the normal routine visits to check your costs, and the mechanic can adjust the labor costs as part of the overall bill. This can also prevent you from paying too much.