Like many car owners, the dreaded “Check Engine” light illuminated on my 2001 Subaru Impreza 2.5 RS dashboard during a regular morning commute. My first thought, and perhaps yours too, was a groan and the looming question of “what now?”. Fortunately, I had invested in an Actron CP9175 OBD2 AutoScanner a year prior when a catalytic converter code appeared. This time, plugging in the Actron Obd2 Autoscanner Cp9175 Error Code reader revealed a different culprit:
P0328
Knock Sensor 1 Circuit High Input Bank 1 or 1 Sensor
This unfamiliar error code, P0328, signaled the start of a new diagnostic journey. It pointed towards the knock sensor, a component I hadn’t dealt with before. This article details my experience diagnosing and resolving the P0328 error code using the Actron CP9175, hoping to guide you through a similar situation.
Understanding DTC P0328 and Knock Sensors
The P0328 error code, as read by your Actron OBD2 autoscanner CP9175, specifically indicates “Knock Sensor 1 Circuit High Input (Bank 1 or Single Sensor)”. But what does this actually mean?
A knock sensor is a crucial component in modern engines. Its primary function is to detect engine knocking or detonation. Knocking is abnormal combustion in the engine cylinders, which can be damaging if left unchecked. The knock sensor listens for these vibrations and sends a signal to the engine control unit (ECU). If excessive knocking is detected, the ECU retards the ignition timing to protect the engine from damage.
A “Circuit High Input” for the P0328 code suggests that the voltage signal from the knock sensor circuit is higher than expected. This could be due to several reasons:
- Faulty Knock Sensor: The sensor itself might be malfunctioning and sending an incorrect signal.
- Wiring Issues: Damage to the wiring harness, connectors, or grounding issues in the knock sensor circuit can cause signal problems.
- ECU Malfunction (Less Likely): In rare cases, a problem with the ECU could misinterpret the sensor signal.
In most DIY scenarios, especially when using an Actron OBD2 autoscanner CP9175 error code reader and encountering P0328, the issue often lies within the knock sensor or its wiring.
Diagnosing P0328 with Actron CP9175 OBD2 AutoScanner
The Actron CP9175 OBD2 AutoScanner is an invaluable tool for DIY car diagnostics. It allows you to quickly read error codes like P0328 and provides a starting point for troubleshooting. Here’s how I approached the diagnosis, mirroring my original experience while offering more structured steps:
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Read the Code: Connect your Actron CP9175 to the OBD2 port in your car (usually under the dashboard). Turn the ignition to the “ON” position (engine off) and follow the scanner’s instructions to read the Diagnostic Trouble Codes (DTCs). Confirm the P0328 error code is present.
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Visual Inspection: Before jumping to sensor replacement, perform a visual inspection. Check the knock sensor wiring for any obvious damage:
- Wiring Harness: Look for frayed, cracked, or melted wires near the knock sensor and along the wiring path.
- Connectors: Ensure the connector at the knock sensor and the connector at the ECU (if accessible) are securely plugged in and free from corrosion.
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Resistance Test (Advanced): If the visual inspection doesn’t reveal issues, a resistance test of the knock sensor can be performed. However, proceed with caution and consult your vehicle’s repair manual for specific instructions and safe testing procedures. In my initial attempt, I found the resistance readings to be erratic, which can be common and not definitively conclusive without proper technique and reference values.
It’s important to note that accurately measuring resistance on a knock sensor can be tricky due to high impedance. Ensure your multimeter is functioning correctly and you are making good contact with the sensor terminals.
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Clear the Code and Monitor: Using your Actron CP9175, clear the P0328 error code. Drive your vehicle under normal conditions and see if the “Check Engine” light and the P0328 code reappear. In my case, the code initially stayed away for a short period, only to return later, indicating a persistent issue.
If the code returns after clearing and visual inspection, and especially if you suspect the sensor is original and old, replacement is often the next logical step.
Step-by-Step Knock Sensor Replacement
Based on the recurring P0328 error code and the age of my Subaru, I decided to replace the knock sensor. Here’s a simplified step-by-step guide based on my experience, which you can adapt for your vehicle (always consult your repair manual for specific instructions):
Tools You’ll Need:
- Actron CP9175 OBD2 AutoScanner: For clearing the code after replacement.
- Ratchet
- Extender
- Socket Adapter
- 12mm Socket (or the correct size for your knock sensor)
- New Knock Sensor (Part number: 22060AA070 for my 2001 Subaru Impreza 2.5 RS, but verify for your specific vehicle).
Replacement Steps:
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Locate the Knock Sensor: The knock sensor is typically screwed into the engine block. In my Subaru Impreza 2.5 RS, it was located under the throttle body cables. Refer to your repair manual for the exact location on your vehicle.
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Disconnect the Connector: Carefully disconnect the electrical connector from the knock sensor. There might be a clip or tab to depress to release the connector.
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Remove the Old Sensor: Use the ratchet, extender, socket adapter, and 12mm socket to carefully unscrew the old knock sensor from the engine block.
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Install the New Sensor: Screw in the new knock sensor by hand initially to avoid cross-threading. Then, use the ratchet and socket to tighten it to the torque specification recommended in your repair manual. Do not overtighten.
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Reconnect the Connector: Reconnect the electrical connector to the new knock sensor, ensuring it clicks into place securely.
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Clear the Error Code: Use your Actron CP9175 OBD2 AutoScanner to clear the P0328 error code.
After the Replacement: Clearing the Code and Monitoring
After replacing the knock sensor and clearing the code with my Actron CP9175 OBD2 AutoScanner, the “Check Engine” light stayed off. It’s crucial to monitor your vehicle after the repair. Drive under various conditions to ensure the P0328 error code does not return.
In my case, as documented in the original post, the P0328 code did not reappear after the knock sensor replacement, proving to be a successful DIY fix.
Alternative Issues and Troubleshooting Tips
While replacing the knock sensor often resolves the P0328 error code, especially when diagnosed with an Actron OBD2 autoscanner CP9175 error code reader, consider these alternative issues:
- Connector Problems: As one commenter pointed out, sometimes the issue isn’t the sensor itself, but the connector. Check for corrosion, loose pins, or damaged wires right at the connector. In some cases, cleaning or repairing the connector can solve the problem.
- Wiring Issues: Thoroughly inspect the wiring harness for any breaks, shorts, or damage. A wiring fault anywhere in the circuit can trigger the P0328 code.
- Genuine vs. Aftermarket Sensors: While aftermarket sensors can be cheaper, consider using a quality replacement sensor from a reputable brand to ensure proper function and longevity.
If you’ve replaced the knock sensor and checked the wiring, and the P0328 code persists, further professional diagnosis might be necessary to rule out more complex issues like ECU problems.
Conclusion
Encountering a “Check Engine” light and the P0328 error code can be concerning, but with a systematic approach and tools like the Actron CP9175 OBD2 AutoScanner, DIY diagnosis and repair are often achievable. In my experience with the Subaru Impreza, a faulty knock sensor was indeed the culprit, and replacement proved to be a straightforward solution. By understanding the function of the knock sensor, utilizing your Actron OBD2 autoscanner CP9175 error code reader effectively, and following a logical troubleshooting process, you can confidently tackle the P0328 code and get back on the road.