Your car has a ton of moving parts and sensors for those parts that all work together to keep your engine running smoothly and efficiently. These sensors regulate things like emissions, ignition timing, transmission shifting, fuel management, and other important functions of the engine.
One sensor that has a particular impact on a variety of systems in your car includes the knock sensor. This sensor works like a sophisticated listening device for your engine. It senses when sounds inside are off-kilter and adjusts accordingly to help prevent engine damage.
You’ll find your cars works less efficiently, becomes louder, and doesn’t accelerate as well if the knock sensor has gone bad.
You’ll also discover that if this sensor isn’t working properly, significant damage can be done to your engine, which may destroy it.
What is a Knock Sensor?
The knock sensor is a little knob-like thing that’s linked to your car’s engine. And this little piece does exactly what the name indicates: it senses knocks in the engine. That knocking is kind of like when a marble hits metal (that metallic sort of ding that nobody wants to hear) since it means something is wrong.
A knock sensor is made up of piezoelectric materials – crystals that generate voltage when impacted. This is basically the same concept as a barbecue igniter.
The voltage is monitored by the engine’s computer. When irregularities are detected, the computer then corrects the timing in variable valve timing engines or triggers a diagnostic trouble code in older cars.
What Does a Knock Sensor Do?
This piece of your car engine has three main purposes.
A knock sensor has the important job of making sure that your engine is getting as much power as necessary, and that your fuel economy is the best possible for your particular engine.
The knock sensor lets your engine run with the ignition timing as far advanced as possible since this little piece is designed to tell the engine when there’s pinging. That pinging is what tells the car’s computer to retard the engine so that it doesn’t go overboard.
In other words, the knock sensor tells the computer in your car when to stop advancing the engine timing and keeps it in check so that it doesn’t ping.
Another way to state this is that your knock sensor senses preignition. The pre-detonation of the air/fuel mixture causes a spark knock in the engine, and that’s what the knock sensor responds to.
The flame front moves out from the spark plug to the ignition point, and pressure waves in the chamber crash into the pistons. This is what causes that knock, or ping that indicates the timing is too far advanced.
Two other things can cause this ping, including fuel with a low octane rating, or overheating in the engine. It may sometimes be caused by hot carbon deposits on the cylinder head or pistons, which raise compression.
The knock sensor in your car is also responsible for monitoring the overall performance of your engine. If the sensor discovers a problem in the performance, it will send a signal to your car’s computer. This is another reason the knock sensor may light the “check engine” light on your car’s dashboard.
Ultimately, it could be said that the knock sensor on your car is for protecting your car’s engine against engine knock. So, if the knock sensor is bad, it can’t properly regulate the engine. This is what results in your car vibrating, and that knocking sound.
The knocking can actually destroy your car’s gaskets, plugs, pistons, rods, and valves.
The knock sensor is also very important for your car’s fuel efficiency. Since the knock sensor deals with the fuel-to-air mix and balancing the timing of the engine, the sensor affects the mileage because it optimizes the fuel-economy through optimizing the power the engine uses.
Where is the Knock Sensor Located?
You’ll find the knock sensor on the cylinder, intake manifold, or the engine block. It’s positioned in one of these places so that it can successfully sense unusual pulsations caused by pre-ignition.
How Can You Tell When a Knock Sensor Goes Bad?
There are a number of indicators that your knock sensor has gone bad. Here’s a fairly comprehensive list of things to look out for.
If there’s an unusual knocking in your car, especially at higher speeds, like during interstate driving, you probably have a bad knock sensor. This knocking sounds like loud thumping, which gets louder over time as the knock sensor goes un-replaced. This sound is the result of air and fuel igniting inside the cylinder, instead of reaching the point of combustion.
Besides the actual sound of knocking in your engine, which you may not always be able to hear because of road noise, there are a few other things you can notice.
The Check Engine Light
Typically, your knock sensor will trigger the “check engine” light, when it goes bad. Low octane fuel, however, can also cause that light to trigger, because of a false reading. So, if you notice this light going on, use a higher grade fuel to see if the problem persists. If it does, consult a mechanic.
The Feel of the Car
When you’re behind the wheel of a car with a bad knock sensor, you can notice that the engine just doesn’t feel right while driving at speed. This can happen both when the car is carrying a heavy load, or even when it’s a light load.
If you notice that the engine just seems off, even if the dashboard isn’t lit up, you should have your car checked out by a mechanic, as it’s likely to be a knock sensor issue.
A bad knock sensor can also cause some significant acceleration issues. This might include the engine dragging, hesitating, or jerking, specifically while increasing speed.
Again, the check engine light might not be lit, so if there are some consistent acceleration issues, you should get the car checked out.
Loss of Power
In case you’re too busy to bring your car to a mechanic at some of the other signs, your computer may pretty much force the issue. If the car’s computer senses that the knock sensor isn’t working properly, it could very well lose power. The level of power you lose will be determined by the octane limit of your engine, and how heavily the engine relies on the knock sensor input.
High compression and flex-fuel engines will lose the most power. That’s because the loss of power slows the timing and keeps the transmission out of drive until the sensor works properly.
This loss of power is designed to help you get safely somewhere without destroying your car engine. You won’t be able to go far, though, so be sure to find a mechanic as close as possible, or you’ll have to get towed.
Bad Fuel Economy
One of the most annoying symptoms of a bad knock sensor is a significant decrease in fuel economy. Your knock sensor helps you avoid burning through fuel too quickly, so when it pops out, you start having to fill up more often.
If you notice that you’re just not getting as much out of your gas these days, you should immediately take the car to a mechanic to have it check out. Be sure to tell the mechanic the drop-in fuel economy so that she knows what’s going on with the car.
You’ll also find a number of other symptoms show a bad knock sensor. Any combination of these may be happening, usually including the ones mentioned above.
- The engine misfires when started.
- The engine shakes and vibrates when started.
- The engine emits strong exhaust.
- There’s a burning smell due to the detonation in the cylinders
Why You Need to Replace Your Knock Sensor if it Goes Bad
When it comes down to it, your engine needs the knock sensor to protect it, maintain it, and run most efficiently. Preignition can cause serious damage. When you have a bad knock sensor for an extended period of time, you could wind up destroying your car’s engine.
Your Car’s Knock Sensor: A Critical Piece of Engine Efficiency and Safety
The knock sensor is a small knob-like piece that is attached to the intake manifold, cylinder, or engine block. It’s placed hear so that it can “listen” to your engine and detect dangerous issues that could destroy the engine.
There are a number of symptoms that help indicate that your knock sensor is malfunctioning. Some of these include lower fuel-economy, strong exhaust emissions, shaking engine, or, of course, the tell-tale knocking sound that the sensor is named for.
If you notice that your car is demonstrating any of these issues, including a lit “check engine” light, you should immediately take your car to a mechanic to ensure that you don’t damage and destroy the engine.