Knock Sensor Replacement Cost

Cost at the Mechanic: $100-$400

• Parts: $20 to $150
• Labor: $80 to $250

An engine knock sensor replacement can take anywhere from 20 minutes to three or four hours, depending on how easy or difficult the sensor is to reach on your particular vehicle. Be prepared to pay for a full hour of labor even if it takes less time since this is the minimum labor cost some shops will charge. The knock sensor is usually just bolted to the side of the engine, so once it’s within reach, it doesn’t take long to replace.

The mechanic should also check for damage in the wiring and the harness that plugs into the knock sensor. This could cause the same problems as a bad sensor.

Cost to DIY: $150-$250

• Difficulty Level: Beginner-Intermediate
• Parts Needed:
  • Engine knock sensor unit

Replacing an engine knock sensor is relatively simple, so you can save money by replacing it yourself. The job is typically as simple as unplugging and unbolting the old sensor, then bolting the new one on. You may need to remove additional components to gain access to the knock sensor, which could complicate this job. Be sure to inspect the wiring and harness for damage, and repair or replace them if necessary.

What Is a Knock Sensor?

The knock sensor detects the symptoms of engine knock. Knocking is a common term for pre-detonation, which is when the air/fuel mixture inside the cylinder combusts earlier than it’s supposed to. This causes poor fuel efficiency, reduced power, and could lead to serious internal engine damage if the problems causing the engine to knock are not addressed.

The knock sensor works by detecting the specific vibrations associated with pre-detonation inside your engine. It reports any abnormalities to the engine management computer, which then attempts to correct the situation that’s causing the knocking by adjusting the timing, air/fuel mixture, and other factors. If the data coming from the knock sensor doesn’t make sense, the computer will detect this error and turn on the check engine light. You will also see the check engine light if the sensor is working properly, the computer has made all the adjustments it can to address the knock, and the problem still exists. This is where the FIXD scanner and app are useful to help you determine what’s causing the knock.

The most common cause of engine knock is using lower octane fuel than recommended. It’s tempting to use low-octane fuel to save a little money. But many modern engines require premium fuel, and running lower grade fuel than recommended will cause knocking or even damage to the engine. Check your owner’s manual to find out what your vehicle’s octane requirements are, and do not use any fuel with a lower octane rating than recommended.

What Does a Knock Sensor Replacement Include?

The knock sensor is usually just bolted to the side of the engine, so the job is little more than unplugging and removing the old sensor, then replacing it with a new one. The area where the knock sensor bolts onto the engine may need to be cleaned, particularly in northern areas where vehicles are prone to rust. This could also make the sensor more difficult to remove.

As mentioned above, the wiring and harness should also be inspected. Damage to these can cause similar problems as a failed sensor. Replacing the sensor won’t fix the problem if the wiring itself is damaged.

What Happens If You Don’t Replace a Bad Knock Sensor?

If your knock sensor fails, the engine management computer won’t get accurate data about knocking inside your engine, preventing it from making adjustments to prevent knocking. Pre-ignition pushes back against the piston as it’s trying to rise inside the cylinder, potentially causing damage to the piston surface, the cylinder walls, or even the crankshaft bearings. What starts as a simple issue can lead to very expensive internal engine damage if the problem isn’t addressed in a timely manner.

How Often to Get a Knock Sensor Replacement

A knock sensor can last for 150,000 miles or more, but it could fail sooner for any number of reasons. If you notice any symptoms that you need knock sensor replacement, you should get it fixed as soon as possible, whether you have a shop fix it or do it yourself.

Common Symptoms You Need to Get a Knock Sensor Replacement

• Check engine light
• Pinging noises in the engine
• Drop in engine power and performance
• Decrease in fuel efficiency

If your check engine light is on, and you pull these OBD2 codes with the FIXD scanner and app, there’s likely a problem with your knock sensor or its wiring:

• P0324: Knock Control System Error
• P0325: Knock Sensor 1 Circuit
• P0328: Knock Sensor 1 Circuit High

Related Maintenance Services

People often get these services performed at the same time as knock sensor replacement:

• Spark plug replacement
• Spark plug wire replacement

Never Miss Important Maintenance Again With FIXD

Get the FIXD scanner and app to follow a customized maintenance schedule based on your vehicle’s mileage, age, make, and model. FIXD sends automatic maintenance alerts to your smartphone, helping you remember important maintenance tasks such as oil changes, tire rotations, knock sensor replacements, and more. FIXD can even track your battery, tire tread, and windshield wiper life to help you make sure that your car keeps working smoothly. Get FIXD today to take more stress out of car care, maintenance, and repairs. It’s that simple.