What is OBD-II Code P0325 – Knock/Combustion Vibration Sensor A Circuit

What is OBD-II Code P0325 – Knock/Combustion Vibration Sensor A Circuit

As a mechanic, one of the most common diagnostic trouble codes (DTC) that I come across is P0325. This code indicates that the knock sensor on a vehicle is malfunctioning, which can lead to decreased engine performance and potentially cause damage if left unresolved.

The knock sensor, also known as the combustion vibration sensor, is responsible for detecting vibrations caused by engine knock or detonation. When the sensor detects these vibrations, it sends a signal to the engine control module (ECM) to adjust the timing and prevent engine damage. If the sensor malfunctions, the ECM may not receive accurate readings, which can lead to engine performance issues and potential damage.

In this article, I will explain what causes P0325 to occur, how to diagnose the issue, and provide steps to repair the problem.

Causes of P0325

The most common cause of P0325 is a faulty knock sensor. However, other potential causes include:

1. Damaged knock sensor wiring or connectors – The knock sensor wiring can be damaged due to wear and tear, rodents, or accidental damage. Damaged wiring can also cause the sensor to malfunction.

2. Failed ECM – In rare cases, a failure in the engine control module can cause P0325 to occur.

3. Failed sensor circuit – The circuit that the knock sensor is connected to can also fail, causing the sensor to malfunction.

Diagnosing P0325

Before attempting to diagnose P0325, it is essential to have access to an OBD-II code reader. Using the reader, you can read the code and determine the underlying issue.

Here are the steps to diagnose P0325:

1. Connect the OBD-II code reader to the vehicle’s diagnostic port.

2. Turn on the ignition but do not start the engine.

3. Retrieve the code by selecting “read codes” on the code reader.

4. Check if there are any additional codes that may be related to P0325.

5. If there are no additional codes, then the issue is likely related to the knock sensor.

6. Inspect the wiring and connectors for any visible damage.

7. If the wiring and connectors appear to be in good condition, perform a voltage test on the knock sensor circuit.

8. If the voltage is not within the manufacturer’s recommended range, then the sensor may need to be replaced.

Repairing P0325

The repair process for P0325 will depend on the underlying issue that caused the code to appear. Here are the steps to repair the most common cause of P0325, a faulty knock sensor:

1. Locate the knock sensor on the engine block. The exact location may vary depending on the make and model of the vehicle.

2. Disconnect the electrical connector from the sensor.

3. Remove the sensor using a wrench or socket.

4. Install the new sensor and tighten it to the manufacturer’s recommended torque specification.

5. Reconnect the electrical connector to the sensor.

6. Clear the code using the OBD-II code reader.

7. Start the engine and check if the code reappears.

Frequently Asked Questions

1. What are the symptoms of a faulty knock sensor?

A faulty knock sensor can cause the engine to hesitate or misfire, decrease in power or acceleration, and produce a knocking or pinging sound.

2. Can I drive with a P0325 code?

While it is possible to drive with a P0325 code, it is not recommended as it can cause further engine damage.

3. Will replacing the knock sensor fix the issue?

In most cases, replacing the knock sensor will fix the issue. However, it is essential to ensure that the wiring and connectors are also in good condition.

4. How much does it cost to replace a knock sensor?

The cost of replacing a knock sensor can vary depending on the make and model of the vehicle and the location of the sensor. On average, the cost can range from $150 to $350.

5. Can P0325 cause the check engine light to come on?

Yes, P0325 will cause the check engine light to come on, indicating there is an issue with the knock sensor circuit.


In conclusion, P0325 is a common diagnostic trouble code that indicates a malfunctioning knock sensor. By understanding the causes, diagnosis, and repair solutions, you can prevent further engine damage and ensure that your vehicle runs smoothly. Remember to always consult a professional mechanic for any engine-related issues to ensure the best possible outcome.

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