Engine knock is one of those things that cause irreparable damage to your engine. Knock happens when there is an issue with combustion timing. In other words, the fuel isn’t combusting at the optimal time. If ignored, engine knock can destroy pistons. Fortunately, all modern engines have a knock sensor that monitors combustion timing and notifies you when something is wrong. If this sensor goes bad, or if it detects out-of-spec readings, it will log a check engine light code — most likely P0325. Today we’ll go over what this code means, how to diagnose it, available fixes, and more. Let’s get to it!

What is the P0325 Code, and What Does It Mean?

The P0325 fault code stands for knock sensor malfunction (sensor 1 bank 1). In other words, it means that the ECU has detected readings from the knock sensor that is outside the normal range.

Although the ECU makes minor adjustments to the air to fuel mixture, if the “knocking” persists, the P0325 fault code will get stored in the ECU. It’s also common for the P0325 code to be associated with a few other engine codes depending on the true cause of the problem.

How Does a Knock Sensor Work?

Knock sensors work by listening to combustion cycles, quite literally. A knock sensor is a type of microphone that is based around a piezoelectric component. This component is capable of discerning normal combustion sound from knock as knock sits higher in the frequency range.

Once higher frequency combustion noises are detected, the information is sent to the which then advances or retards timing to compensate. Due to its nature, almost all knock sensors are mounted somewhere very close to the combustion chambers. Overall, a knock sensor is a simple yet ingenious device that is fairly foolproof as long as all of its parts are in decent working order.

What Happens When a Knock Sensor Goes Bad?

A faulty knock sensor means that there is no way for the ECU to adjust timing to compensate for the engine. Needless to say, that can cause all kinds of issues, including severe engine knock.

Depending on how bad things get, a bad knock sensor could lead to broken pistons, connecting rods, and a whole bunch of other rather important internals. Although the P0325 code doesn’t necessarily imply imminent doom, the mere fact that it can cause the unlikely yet possible issues we’ve just mentioned means that you should definitely try and sort it out sooner rather than later.

What Causes a P0325 Code?

The P0325 fault code is a pretty specific one, and there are only a couple of things that will commonly cause it to trigger the check engine light.

Faulty Knock Sensor

A faulty knock sensor is by far the most common cause for the P0325 code. Almost every internal combustion engine has one fitted either on the engine block or on the intake manifold. Because it’s exposed to excess heat and vibration, it can become faulty and cause the P0325 code to trigger the check engine light.

Engine Running Lean

Another common cause for the P0325 fault code is a lean running engine. We’re not talking about the usual lean condition, though. In most cases, your engine would need to run extremely lean to cause this error.

Since knock happens when the air-fuel mixture is combusting outside the optimal envelope, your fuel trim has to be way out of spec to trigger this code. In other words, there’s a good chance that you’re looking at an issue that has very little to do with the knock sensor itself.

Damaged Wiring

Damaged wiring causes more engine fault codes than people realize. Constant exposure to heat cycles and vibrations from the engine makes the wiring prone to cracking and all kinds of other issues. Disconnected or damaged wiring to the knock sensor will automatically trigger the P0325 code.

Symptoms of P0325 Code

Symptoms of a P0325 engine fault code include everything from engine knock to reduced fuel economy. These symptoms can be caused by other issues as well, which is why you should try and read the fault code before you start throwing parts at your engine bay.

Illuminated Check Engine Light

Almost every fault code triggers the check engine light, and the same applies to the P0325 code. Once the ECU detects a knock sensor malfunction, the check engine light will be illuminated, so as soon as you notice this, your next destination should be a shop or your own garage where you will check stored fault codes in your ECU. If there’s an issue found on knock sensor 1 on bank 1, the P0325 fault code will be visible.

Engine Knock

Noticing engine knocking is a serious symptom that should be taken seriously. That being said, it likely won’t happen the moment the knock sensor goes bad. Either way, you shouldn’t drive a car that’s knocking as doing so will only increase the chances of you having to rebuild the entire engine.

Reduced Engine Performance

Another thing that happens as soon as a knock sensor goes bad is that the ECU returns to default presets. What this means is that the engine operation isn’t optimized, and the car won’t be able to accelerate as well as it could before the issue came up.

You’ll also notice that your car can’t go as fast as it could. This is a common symptom when the air to fuel ratio isn’t ideal.

Reduced Fuel Economy

Reduced fuel economy isn’t caused directly by a bad knock sensor, but by the ECU trying to compensate when it notices the sensor isn’t working properly. The difference in fuel economy won’t be significant, but it will be noticeable.

How to Diagnose and Fix P0325 Code

When it comes to diagnosing the P0325 fault code, it should start by using an OBD II scanner to check for fault codes that can help narrow down the possible cause. In some cases, the P0325 code is a result of a completely different issue.

If the P0325 fault code is the only one stored in the ECU, here’s what you’ll need to do to diagnose the issue and fix it.

Visually Inspect Wiring and Connectors

In a certain number of cases, damaged wiring or disconnected connectors will cause the P0325 code to appear in the ECU and trigger the check engine light on your dash. By visually inspecting the wiring, you’ll might find the cause of the issue.

If a wire is damaged, you’ll need to replace the wire or connector. After doing so, erase the code from the ECU and restart the engine. If the wires were the cause, the check engine light won’t appear again.

Check If The Knock Sensor Is Sending Signals To The ECU

To check the knock sensor 1 on bank 1, you’ll need to use a multimeter. You can also check freeze-frame data related to the knock sensor. This will give you more information about the possible cause of the P0325 code.

If the readings are out of spec, you’re probably looking at a new sensor in your immediate future. If you need to replace the knock sensor, make sure you replace the knock sensor harness as well. Erase the trouble code with your OBD II scanner and test if the issue is resolved.

Check Coolant Temperature Readings

This step is often overlooked, but it’s important to make sure coolant temperature readings are correct. Overheating can cause engine knock which is why it’s of the utmost importance to deal with this issue if it’s the cause for the P0325 code to appear.

You’ll need to do this step only if none of the above steps helped you find the cause for the issue.

Can You Drive with a bad knock sensor?

In some cars, there will be no clear symptoms aside from the check engine light when the fault code P0325 is triggered, but it’s a matter of time when additional damage will occur. That’s why it’s not recommended to drive your car if you find the P0325 code stored in the ECU.

Once the engine knock occurs, the engine will begin to take damage that can ultimately be more costly to repair than towing the car and eliminating the cause of the issue.

Fixing the P0325 Code Requires High-Quality Parts

Considering just how crucial the function of a knock sensor is for your engine, it is the one part you don’t want to cut corners with. Using genuine or OEM replacement sensors is not just recommended, it’s pretty much the only way to go.

We at eEuroparts.com offer a wide range of genuine, OEM, and quality aftermarket parts for your European car. This includes a variety of quality knock sensors. Head over to our store, select your vehicle using our vehicle navigation tool, and search for knock sensors. You’ll be presented with a list of products that are guaranteed to match your car.