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P0165 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


DTC codes are alphanumeric designations used by the vehicle’s On-Board Diagnostic (OBD) system to pinpoint specific issues within various components. P0165 is a DTC related to the O2 sensor circuit on Bank 2, hereinafter referred to as sensors 3 and 4, which are also known as downstream O2 sensors. The sensor will play a vital role in the detection of oxygen concentrations in exhaust gases after they have been exposed to an ionizing catalyst.


A problem with the O2 heater circuit for bank 2, Sensor 3, has been identified by code P0165. The sensor is equipped with an internal heat source, which helps it reach the operating temperature faster, thus increasing its efficiency in providing accurate readings. This code indicates that there are problems with the heater system, which has a negative effect on sensor performance.


  • Faulty O2 Sensor Heater: One of the main root causes of the P0165 code is a faulty heater in the downstream O2 sensor. It’s possible that the heating element is broken, open, or has too much resistance.
  • Wiring or Connector Issues: Damaged or corroded wiring and connectors associated with the O2 sensor heater can disrupt the flow of electricity to the heater element.
  • Internal ECM Issues: On occasion, the Engine Control Module (ECM) might have internal issues that result in the P0165 code.


  • Check Engine Light Illumination: The Check Engine Light illumination on the dashboard of the car is the P0165 code’s most obvious symptom.
  • Decreased Fuel economy: A faulty O2 sensor heater may cause a prolonged warm-up period for the sensor, which may reduce fuel economy.
  • Higher Emissions: As the sensor takes longer to achieve the required working temperature, emissions may rise briefly before they return to normal.


The P0165 code has to be diagnosed using a methodical process:

  • OBD-II Scanner: A skilled mechanic will access the vehicle’s Engine Control Module (ECM) with an OBD-II scanner to extract the recorded DTCs.
  • Visual Inspection: To check for any obvious damage or problems, the technician will visually examine the downstream O2 sensor, along with its wiring and connections.
  • Heater Circuit Testing: To test the resistance of the O2 sensor heater circuit and find any open or excessive resistance, specialized diagnostic equipment may be employed.
  • Cross-checking: To rule out internal problems, the technician may additionally examine the ECM and other relevant components.

Common mistakes

  • Replacing the downstream O2 sensor without first confirming the root cause of the problem, since other factors such as electrical problems or ECM-related problems may be responsible for the code. 
  • Insufficient attention is given to checking related trouble codes, which could provide more information about the problem.

How serious is this?

Although code P0165 does not pose immediate or serious drivability problems, it should not be ignored. In addition, a failure of the O2 sensor heater may result in an extended warm-up time for the sensor and can have an impact on fuel efficiency and emissions control. If this is not remedied, the performance of the engines may be adversely affected, and emissions will increase.

What repairs can fix the code?

repair manuals

  • O2 Sensor Heater Replacement: If the downstream O2 sensor’s heater is found to be broken, the problem may be fixed by swapping the sensor out for a brand-new, high-quality device.
  • Repairing Wiring or Connections: The O2 sensor heater’s wiring and connections can function properly again if any of them are broken or rusted.
  • Dealing with ECM Issues: If the heater circuit problem is due to an ECM issue, repairs or replacement may be required.

Related codes

  • P0135: O2 Sensor Heater Circuit (Bank 1, Sensor 1)
  • P0141: O2 Sensor Heater Circuit (Bank 1, Sensor 2)


On Bank 2, Sensor 3, the P0165 DTC code relates to the downstream O2 sensor heater circuit. Owners and mechanics are empowered to take the necessary steps if they have a clear understanding of the meaning, causes, symptoms, or possible repairs of this code. The optimal performance of the engine, fuel efficiency, and emission control can be maintained by promptly identifying problems and resolving them.

It is vital to ask for the assistance of a professional mechanic if you have encountered P0165 codes or suspect problems associated with O2 sensor heaters so that your vehicle can run properly and efficiently.

P0165 Code – What Does It Mean & How To Fix It