5 Symptoms of a Bad Knock Sensor and Replacement Cost

Engine detonation happens during the internal combustion process if the gasoline in the cylinder explodes and then changes the ignition timing. This detonation is sometimes referred to as engine knocking.

When a vehicle’s engine is started up and detonation occurs, there is a knock sensor that will detect these vibrations and send a voltage signal to the powertrain control module. From there, the module will alter the ignition’s timing and prevent engine detonation.

This will help prevent damage to the engine as it goes through the pre-ignition process. If your knock sensor were to malfunction or go bad in your vehicle, there would be some noticeable symptoms that would present themselves.

Here are five of the most common signs of a faulty knock sensor that you should look out for.

Top 5 Bad Knock Sensor Symptoms

1) Engine Warning Light

One of the first symptoms you might notice is the engine warning light illuminating on your dashboard. You should take this early warning sign seriously and have your vehicle inspected before the problem gets worse.

Of course, there are many reasons why an engine warning light could turn on and a bad knock sensor is one of them. Regardless of the reason, you shouldn’t take the chance of ignoring it for too long or it could have devastating effects on your engine.

2) Loud Sounds

When the knock sensor starts to malfunction, you will hear loud noises coming from the engine that almost resembles thumping sounds. The longer you go without fixing this problem, the louder those sounds are going to get.

The reason this noise occurs is due to the ignition of the air and fuel mixture inside of the cylinder. Normally, the mixture would reach the combustion point instead. Therefore, sounds like this should motivate you to take your vehicle to the mechanic promptly.

3) Bad Fuel Mileage

If you notice that you’re getting fewer miles per gallon than you normally do, then a bad knock sensor could be contributing to that. Again, there are many reasons for why you might get bad fuel mileage.

But if you notice any of these other symptoms in conjunction with bad fuel mileage, then that’s even more reason to believe it is because of a bad knock sensor.

4) Poor Acceleration

When you step on the gas pedal to accelerate your vehicle and it doesn’t accelerate fast, then a bad knock sensor is probably preventing the acceleration from being effective. You can be sure of this if you already have the previous three symptoms occurring.

5) Poor Engine Performance

The worst symptoms from a bad knock sensor will occur when internal engine components become damaged. If you’ve let this problem escalate without replacing a faulty knock sensor, then your vehicle will begin to increasingly drag and jerk around.

There may even be a burning smell coming from the engine and getting into the cabin of your vehicle. Any further use of the vehicle in this condition could result in the entire engine being destroyed.

Then, you’re looking at many thousands of dollars to replace your entire engine. Don’t wait for that to happen. It is much cheaper to just replace the knock sensor.

Knock Sensor Replacement Cost

The good news is that it won’t cost you an arm and a leg to replace a bad knock sensor. If you have a standard economy vehicle, you can expect to pay anywhere from $120 to $500 for replacing your knock sensor. The parts cost will be anywhere from $65 to $200, while the labor costs will be anywhere from $50 to $350.

In most cases, the parts costs and labor costs will be about the same. If you can find a good deal on the labor from an independent mechanic, then maybe you can lower your overall costs considerably.

1 thought on “5 Symptoms of a Bad Knock Sensor and Replacement Cost”

  1. Hello, my 95 corolla has 297967 miles and it has been pinging and knocking when I accelerate. The pinging and knocking is not to loud but it is noticable in hot or cold weather and this happens intermittently. No check light on but I have noticed my fuel economy is not good my car still has good power. Could it still be a bad knock sencor


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