If you own a modern car, chances are it has a knock sensor as part of its engine management system. But what does this small device do, and why is it important for your engine's performance and efficiency? In this article, you'll learn about the function, location, and symptoms of a faulty knock sensor, and how to diagnose and replace it yourself or with professional help.
A knock sensor is a type of piezoelectric sensor that detects abnormal vibrations or noises in the engine, also known as engine knock or detonation. Engine knock occurs when the fuel-air mixture in the cylinders ignites too early or unevenly, causing pressure waves that can damage the engine components. A knock sensor sends a signal to the engine control unit (ECU), which then adjusts the ignition timing, fuel injection, and other parameters to prevent or reduce knock and optimize engine performance and efficiency.
Yes , it's the perfect answer . The knock sensor in internal combustion engines (ICE) monitors vibrations and detects abnormal combustion, known as knocking or pinging. When it senses these vibrations, it sends signals to the engine control unit (ECU), which can then adjust the ignition timing to prevent engine damage and optimize performance.
Assuming normal operation, the flame front during the combustion stage starts from the spark plug and travels down towards the piston. During normal operation, the air/fuel mix inside the cylinder is assumed to have mixed and swirled enough to be uniform, therefore helping the flame propagate properly therefore completing the controlled burn. The force is pushing down on the piston only. If there exist multiple pockets of fuel of varying richness (rich/lean), as the flame front travels down, it ignites those pockets. The pressure waves created have the potential of spoiling that engine's day dramatically if they are severe enough. The characteristic sound of pinging is what the knock sensor picks up and reports.
MSc Student in Product Development | Automotive Engineer | Design Engineering |
Think of your car engine as a coordinated team. The knock sensor takes on the role of the lookout constantly scanning for any signs of trouble, like "engine knock" or "detonation." Once it detects such an issue it promptly alerts the brain of the engine, known as the engine control module. In turn the brain makes adjustments such as determining when to spark the spark plug or how fuel to inject. This swift response acts as a safeguard preventing any damage, to the engine and ensuring operation—just like having a superhero looking out for your cars engine. Causes: Low-quality fuel, high engine temps, incorrect ignition timing, carbon deposits, faulty knock sensor, worn engine components.
Knock sensor is like a microphone mounted directly on the engine. It is designed to pickup engine ping or detonation. The ECU uses this information to optimize injection and ignition timing.
The sensor identifies the high-frequency engine vibrations characteristic of knocking and transmits a signalto the ECU. The aim is to obtain the maximum energy yield by starting Ignition as early as possible.
A knock sensor is usually mounted on the engine block, cylinder head, or intake manifold, close to the combustion chambers. Depending on the engine configuration, there may be one or more knock sensors on different banks or cylinders. The knock sensor is connected to the ECU by a wiring harness, and sometimes has a shield or cover to protect it from heat and dirt.
A knock sensor is a device used in engines to detect abnormal combustion, also known as engine knocking or pinging. When the sensor detects these vibrations or shock waves in the engine, it sends a signal to the engine control unit (ECU) to adjust the ignition timing. The purpose of this is to prevent engine damage caused by excessive knocking, maintain optimal performance, and improve fuel efficiency. Essentially, the knock sensor helps the engine maintain a smooth and efficient combustion process by detecting and responding to abnormal combustion events.
In the past year, there was 2 or 3 position to place the Knock sensor since this was not easy to know exactly where to place the sensor in mechanical simulation. The idea is to place it in the best vibration conductive place, ideally between Cylinder 2 and 3 on a 4 cylinders engine. On V engine you need twice knock sensor. On in line engine with more than 6 cylinders, your need a also at least 2 sensors.
In SI engine, knock control is one of the most important parts of the engine control. Mass-produced piston combustion engines are usually equipped with one or sometimes two knock sensors located on the engine block The signal from them is filtered and sent to the ECU (electronic control unit), which decides whether the cycle is knocking or not.
The knock sensor detects vibrations on the engine block to inform the engine control unit, allowing it to adjust the ignition timing and eliminate engine knock. The knock sensor is directly installed on your car's engine block.
A knock sensor is a vibration sensor that constantly transmits variable alternating voltage such as frequency and voltage to the ECU. The ECU is programmed to recognize certain types of voltage peaks and frequencys as knock, determined by the factory through tests, depending on the transmission medium, the placement of the sensor on the cylinder block and the tightening torque. Most naturally aspirated 4R otto engines have a single sensor placed on the center of the block between cylinders 2 and 3, but there are exceptions with two sensors placed between 2 cylinders each.
A faulty knock sensor can cause a range of issues with your engine, such as reduced power and acceleration, poor fuel economy, increased emissions, engine hesitation or misfire, and even a check engine light or trouble codes. Additionally, you may hear a knocking or pinging noise from the engine. It's important to note that some of these symptoms may be caused by other problems such as bad spark plugs, fuel injectors, or oxygen sensors. Therefore, it's essential to perform a proper diagnosis before replacing the knock sensor.
A faulty bad knock sensor will show illuminated engine light (CEL) on dashboard. A failed knock sensor will register a trouble code and send it to the engine control unit (ECU), which can be scanned from ECU’s memory Another sign of a bad knock sensor is an engine misfire. This means that the engine is not running smoothly and efficiently, and may lose power, hesitate, or stall under acceleration. Another sign of a bad knock sensor is a knocking or pinging noise from engine. This noise is caused by pre-ignition or detonation, which is when the air-fuel mixture in the cylinder ignites before the spark plug fires. The next sign of faulty knock sensor is more fuel will get burnt. Fuel efficiency drops. The next sign is engine damage.
Not all knock sensors that are failed will turn on the CEL/MIL. Most vehicle systems only look at the voltage produced by the knock sensor. If it is in the acceptable range it gets a pass. Sometimes the sensors are too sensitive and alarm prematurely or too frequently. On the other end of the spectrum are sensors that won't even trigger when there is an audible ping. In the first case the only symptom is reduced engine power as timing gets pulled back to try and reduce the "detected" knock. In the second case the only symptom is failed emissions tests and a possible audible clatter.
To diagnose a faulty knock sensor, you'll need a scan tool or a multimeter. A scan tool can read the trouble codes stored in the ECU, which may indicate a knock sensor malfunction or circuit problem. A multimeter can measure the resistance and voltage of the knock sensor and its wiring, and compare them to the specifications in the service manual. If the readings are out of range, the knock sensor or its wiring may be faulty.
Knock sensor failure can be caused by different reasons: Internal short circuits, Breaks in wiring, Wiring short circuit, Mechanical damage, Incorrect mounting, and Corrosion. Check the wiring to the control unit by checking continuity and short circuit to frame for every wire to the control unit plug. Check with the oscilloscope when the engine is warm. Connect the test probes of the oscilloscope. The oscillogram must produce a signal with considerably enlarged amplitude. If the signal is not clear, tap gently against the engine block near the sensor. If the knocking is not detected, this indicates a defective sensor or circuit. Further diagnosis is to be carried out as per product service manual. ?
One thing I've found helpful is having an oscilloscope handy when carrying out diagnostics on knock sensors. As the signal frequencies tend to be high, most multimeters will fail to register true representative outputs.
Knock sensors produced in the past ten years have very low failure rates. Most failures are due to wiring and connection issues. Oil and coolant leaks seeping into the wiring harness and breaking down the insulation on the wires going to the knock sensor are some of the most common failures I have found. This is exacerbated on V engines where the sensors are mounted on the outside of the block under the exhaust manifolds. Loose/spread terminal connectors due to vibration and improper strain relief for the harness going to the sensor are the second most common issues I have found.
To replace a faulty knock sensor, you'll need to locate it on your engine, disconnect the wiring harness, and unscrew it from its mounting position. You may need to remove some components, such as the intake manifold or the valve cover, to access the knock sensor. You should also inspect the wiring harness for any signs of damage or corrosion, and replace it if necessary. Then, you can install the new knock sensor, reconnect the wiring harness, and clear the trouble codes with a scan tool. You may need to drive your car for a few cycles to reset the ECU and monitor the engine performance.
Replacing a faulty knock sensor refer the service manual and follow these steps - check knock sensor by keeping engine is in off condition on a level surface with parking brake is engaged, and allow the engine to cool. Locate the sensor near the intake manifold on the engine block, and attached to the sensor will be a wiring harness. Now remove the wiring harness by gently squeezing the tabs holding it in place and moving it to one side. Use an adjustable wrench to remove the sensor by turning it counterclockwise and pulling it out by hand. Install the new knock sensor and tighten it in place by going clockwise with your adjustable wrench. Reattach the wiring harness to the new sensor. Reattach any components removed during disassembly.
Maintaining and troubleshooting your knock sensor is important to ensure optimal engine performance. Make sure you use the correct octane rating for your fuel, as lower octane fuels can cause engine knock. Additionally, keep your engine clean and well-tuned, as carbon deposits, worn spark plugs, or faulty injectors can also cause engine knock. Be wary of using aftermarket knock sensors or wiring, as they may not be compatible with your ECU or engine specifications. Furthermore, if you suspect a faulty knock sensor, don't ignore it as it can lead to serious engine damage or failure.
Use high-quality fuel with proper octane rating. Octane rating is a measure of how resistant a fuel is to knocking. Keep engine clean and well-maintained. Carbon buildup on the piston crowns, cylinder walls, valves, and spark plugs can create hot spots that can trigger engine knock. Change oil and oil filter regularly. Maintain cooling system to avoid overheating of engine and perform periodic maintenance. Replace faulty spark plugs or wires. Listen for any unusual noises from your engine and address them promptly. check your dashboard for any warning lights or messages. You should also scan your ECU for any trouble codes related to the knock sensor or other sensors.
Engines are designed to run at rated power and torque, so regularly running an engine at high speed and load for short periods will help performance over the longer term by keeping mechanical parts moving freely. High gas temperatures and velocity will maintain engine breathing, minimise deposits in the gas path and help maintain spark plugs for smoother running. Only running an engine at low to part load tends to cause long term issues and a loss of performance. Think of it like doing your 5k weekly Park run to keep the doctor away.
Not all knock sensor activations are caused by pre-detonation or combustion issues. Pay close attention to belt systems, motor mounts and mounting hardware. Anything that can cause a tapping style rhythmic vibration can be picked up by the knock sensors.