How to Fix P0521 Engine Oil Pressure Sensor/Switch Circuit Malfunction

The P0521 error code refers to an engine oil pressure sensor/switch circuit malfunction. This error code typically indicates an issue with the oil pressure sensor or the related circuit.

If you’ve encountered this error code, don’t worry. In this article, we will guide you through the process of fixing the P0521 error code step by step.

By following these instructions, you can resolve the issue and ensure the proper functioning of your vehicle.


The P0521 error code can be frustrating, as it can lead to concerns about the engine’s oil pressure and potential damage to the engine.

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However, it’s essential to address this issue promptly to avoid any further complications. Let’s dive into understanding the P0521 error code and the necessary steps to fix it.

Understanding the P0521 Error Code

The P0521 error code specifically relates to the engine oil pressure sensor/switch circuit. It indicates a malfunction in the circuit, which can lead to inaccurate readings or a complete failure of the oil pressure sensor.

The engine control module (ECM) detects this malfunction and triggers the check engine light, alerting you to the problem.

Causes of P0521 Error Code

Several factors can contribute to the occurrence of the P0521 error code. These may include:

  1. Faulty oil pressure sensor: Over time, the oil pressure sensor can wear out or become damaged, leading to inaccurate readings or a complete malfunction.
  2. Wiring issues: Damaged or corroded wiring connections can disrupt the communication between the oil pressure sensor and the ECM, triggering the P0521 error code.
  3. Low engine oil level: Inadequate engine oil can result in lower oil pressure, causing the oil pressure sensor to send incorrect signals to the ECM.

Symptoms of P0521 Error Code

When the P0521 error code appears, several symptoms may accompany it. These symptoms can include:

  • Illumination of the check engine light: The most common indicator of the P0521 error code is the activation of the check engine light on the dashboard.
  • Fluctuating oil pressure readings: You may notice inconsistent oil pressure readings on the gauge or dashboard display.
  • Engine performance issues: In some cases, the P0521 error code can affect the engine’s performance, resulting in reduced power or rough idling.

Diagnosing the P0521 Error Code

Before proceeding with the fix, it’s crucial to accurately diagnose the cause of the P0521 error code. Here are the steps to diagnose the issue:

  1. Connect a diagnostic scanner: Use an OBD-II scanner to retrieve the error code and gather information about the P0521 error.
  2. Check oil pressure sensor connections: Inspect the wiring connections between the oil pressure sensor and the ECM for any signs of damage, corrosion, or loose connections.
  3. Test the oil pressure sensor: Use a multimeter to measure the resistance across the terminals of the oil pressure sensor. Compare the readings with the manufacturer’s specifications to determine if the sensor is faulty.

Fixing the P0521 Error Code

Once you have diagnosed the issue and confirmed that the P0521 error code is related to the oil pressure sensor/switch circuit malfunction, you can proceed with the following steps to fix it:

Step 1: Check the Oil Pressure Sensor

Start by locating the oil pressure sensor, which is typically located near the engine block. Inspect the sensor for any signs of damage, leaks, or oil residue. If the sensor appears damaged or worn out, it needs to be replaced.

Step 2: Inspect the Wiring

Thoroughly examine the wiring harness connected to the oil pressure sensor. Look for any frayed wires, loose connections, or corrosion. Repair or replace any damaged wiring as necessary.

Step 3: Replace the Oil Pressure Switch

If the oil pressure sensor is faulty, it’s recommended to replace it with a new one. Follow the manufacturer’s instructions to install the new sensor correctly. Ensure the wiring connections are secure and properly attached.

Step 4: Resetting the Error Code

After completing the necessary repairs, you’ll need to reset the error code using an OBD-II scanner or by disconnecting the battery for a few minutes. This will clear the error code and allow the ECM to reevaluate the sensor’s performance.


Fixing the P0521 error code related to the engine oil pressure sensor/switch circuit malfunction is essential for maintaining the optimal performance of your vehicle. By following the steps outlined in this guide, you can diagnose and resolve the issue with relative ease. However, if you’re unsure or uncomfortable performing these steps yourself, it’s recommended to consult a professional mechanic for assistance.


Q: Can I continue driving with the P0521 error code?

A: While it’s technically possible to drive with the P0521 error code, it’s not recommended. Ignoring this error code can lead to inaccurate oil pressure readings, potentially causing engine damage. It’s best to address the issue promptly.

Q: How much does it cost to fix the P0521 error code?

A: The cost of fixing the P0521 error code can vary depending on several factors, including the specific vehicle, labor costs, and whether you choose to replace the sensor yourself or have it done by a professional. It’s advisable to consult with a mechanic or service center to get an accurate estimate.

Q: Can a DIY enthusiast fix the P0521 error code?

A: If you have the necessary tools, technical knowledge, and confidence, it’s possible to fix the P0521 error code as a DIY project. However, keep in mind that working on the engine or electrical systems of a vehicle requires expertise, and any mistakes can have serious consequences. If you’re unsure, it’s best to seek professional help.