P0031: Oxygen (A/F) Sensor Heater Control Circuit Low (Bank 1 Sensor 1)

If your OBD-II scanner indicates an error code P0031, this means that you have an issue with your O2 sensor number one. For many vehicles, this is also known as an air/fuel ratio sensor. Here are a few steps to help you our if you're wondering, "How do I fix trouble code P0031?" Follow these steps to restore your air/fuel sensor and remove the DTC and Check Engine light from your dashboard.


Signs of a P0031 Error Code

If your vehicle includes an air/fuel ratio sensor, it’s main function is to compare your vehicle’s air/fuel ratio to the outside air. Although it functions most effectively when the exhaust gas temperature isn’t too low, most have a heater to ensure accurate air/fuel readings. This heater plays a major role in the overall efficiency of your engine, particularly in cooler climates.

When you receive trouble code P0031, the heater for this sensor has a low resistance reading. Usually the resistance is below 0.8 A. This means a number of things could be wrong with your air/fuel sensor and/or heater:

  • Damaged heater
  • Improper electrical connection
  • Failed ECM/PCM

The first sign you’ll receive of this issue is a malfunction indicator lamp, or your Check Engine light turning on. An illuminated Check Engine light could mean a variety of things, so be sure you have an OBD-II scan to verify the issue is a P0031 error code.

Determining the Cause

Once you’ve determined your vehicle has a OBD-II scanner error code P0031 problem, there’s a few steps you need to identify the proper solution. A full diagnosis requires you to check the relay and fuse for your air/fuel sensor heater, as well as inspecting the wiring, the sensor and the heater itself.

The circuit feed should measure 12 volts. An improper voltage reading could point to damaged wiring. Check connectors, inspect the ground circuit, and look for any frayed, cut, or loose wiring. You should also measure the resistance of the heater circuit.

The exact resistance you’re looking for varies depending on the make and model of your vehicle. Refer to your service manual for the correct ohms and voltage for each circuit. Not all vehicles require a resistance reading under 0.8 A for this DTC to appear.

How to Fix P0031

The most common way to fix your vehicle’s performance and remove this DTC is replacing the engine bank 1 sensor 1, also known as the air/fuel sensor. As your vehicle ages, this sensor and the heater can wear out over time, reducing its efficiency and causing error code P0031.

Comprehensive Solutions

If this doesn’t solve your error code, there are some more in-depth solutions you can take to solve the issue. You could have a failure in your PCM or ECM. The power-train control module and engine control module are central systems that work with your air/fuel sensor and a variety of other electrical devices and sensors. A failure in either of these modules could affect a number of systems and cause error code P0031 or a number of other related codes.

A relatively minor, yet more time-consuming solution is to inspect the wiring for your air/fuel sensor. A single frayed wire, loose connection or damaged fuse could cause this error code to appear. Carefully inspect all the wiring leading to the sensor and any wiring related to your PCM and ECM.

After you’ve searched these common and more complex solutions, you should understand what does the code P0031 mean? This sensor plays an integral role in the overall air/fuel efficiency of your vehicle, so it’s important to replace the sensor or solve the DTC as soon as you can. You can get the parts you need at your local AutoZone Store.
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