Knock Sensor Replacement Cost

The knock sensor is able to detect the vibrations, such as hitting a bump in the road, and will then send this information of how large this vibration was back to the engine control module, the onboard computer inside of your car.  With this information, while sensing the frequency of the vibrations, the engine control module can then adjust the timing slightly to help the engine run smoother, or in the case of a larger-than-average vibration, the car will illuminate the check engine light.

Threaded into a hole inside of the engine block, underneath the intake manifold, or the cylinder head, all depending on your car’s setup, when this part isn’t operating as it should, then the engine will begin to knock, or in the case of acceleration, the “check engine” light will illuminate.

“100_1441” (CC BY 2.0) by Dyl86

Knock sensor replacement cost

The costs of replacing a knock sensor will depend on the car you drive, your geographical region and the mechanic you hire, as with most car repairs.  Based on these factors, the costs to replace a knock sensor professional can range anywhere from $175 to $500.  Labor tends to be in the $125 to $300 range, whereas parts, again, highly dependent upon the car you drive, can range anywhere from $30 to $80+

Tom and Ray, via the Virginian-Pilot, noted the repair should be in the $200 range.

What does the knock sensor do?

Every time vibration is sensed by the knock sensor, generally a bump in the road or when a vehicle door shuts, it will send a signal to your car’s onboard computer, known as the engine control module, reporting how much of a vibration was present.  The onboard computer, which is programmed to expect a specified range, will illuminate the check engine light in the case of a large enough vibration, outside of this specified range.

How is a knock sensor replaced?

To confirm the knock sensor is, indeed, the culprit, your mechanic will first want to scan your car’s computer to read the OBD code, an on-board-diagnostic trouble code that’s able to tell the mechanic exactly what the problem is.  Common codes, according to RepairPal.com, includes P0324, P0325 and P0326.  Aside from this, he or she will also visually inspect the sensor, along with the wiring, to note any associated problems, especially if the electrical connectors or the wiring harness is working properly.

Once confirmed the part is the problem, then the mechanic will unscrew the sensor, unplugging it from the wiring harness, after the car has been raised, and in most cases, there is generally only one electrical connector per knock sensor, but with some designs, there could be another knock sensor located on the engine.   Before attaching the new knock sensor, dielectric grease is applied on the threads for lubrication and the new part is installed, usually with the help of a wrench.

Also, dependent on the engine design, the oil may need to be drained in some cases to change the knock sensor.  In this scenario, the oil filter and an oil change may be recommended as well.

The entire process is pretty straightforward and will take less than 30 minutes to complete.

Tips to know

The most common cause for a knock sensor symptom often relies upon the check engine light illuminating on the dashboard, which will have to be confirmed via an OBD scan.  Other symptoms may include a loud knocking coming from the engine, poor fuel mileage and/or decreased performance when accelerating.  Failing to change the sensor can often cause the engine to run hot and/or burn an excessive amount of fuel.

For most cars, the knock sensor can easily last more than 150,000 miles, but as with any part, this is highly dependent on the car you drive.

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