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P0131 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.


O2 Sensor Circuit Low Voltage Bank 1 Sensor 1


Pulling this trouble code means there is something wrong with your engine’s primary oxygen sensor circuit responsible for proper fuel/air mixture. It may be wiring, a connector or other damage to the circuit, and occasionally the O2 sensor itself is the issue. For this error to code, the ECM is detecting less than that standard 1 volt passing through the O2 sensor circuit.


Fortunately, a P0131 has only a few potential causes. Here’s a brief list:

  • The O2 sensor itself has failed
  • The circuit cannot pass sufficient voltage
  • There is a faulty connection between the O2 sensor and the ECM
  • The wiring could be broken or have a loose connector
  • The wiring harness insulation could be worn or missing
  • There is a short in the ground wire of the O2 sensor wiring harness


Here’s what you can expect to experience when driving a vehicle with a P0131 trouble code.

  • Vehicle runs less efficiently (rough idle, stalling when idle, etc.)
  • Low voltage in the 02 sensor circuit or other parts of the electrical system
  • Bad fuel/air mixture (strong odor of fuel from the exhaust)
  • Missing at steady throttle (engine is misfiring)
  • Hard starting due to lack of oxygen in the ignition cycle
  • Poor gas mileage (too much fuel being used in each cycle because the mixture is off)


To properly correct this issue, you need an efficient, step-by-step troubleshooting process so you can fix it right the first time. Here’s a rundown of how to diagnose the root cause of a P0131:

Start by connecting an OBDII scanner and pulling all trouble codes, making certain to note and save the freeze-frame data. That data will allow you to attempt to recreate the conditions that triggered the code in the ECM when you take your test drive.

After you pull codes and save freeze-frame data, clear the codes and hook your scanner back up. If the P0131 comes back on, the circuit is reading excessive resistance, or the circuit voltage is out of range, the problem is confirmed.

Next up, you need to check the wiring and connectors on the O2 sensor circuit to see if it is worn, damaged or broken.

Finally, after making a thorough wiring check, you need to test the wiring with a multimeter to ensure the correct voltage and resistance are present when the circuit is active. Voltage should be less than 1 Volt, and the resistance varies by manufacturer specifications. If everything still checks out, the source of the problem is the O2 sensor and it will need to be replaced.

Common mistakes

Everyone makes mistakes, but many can be avoided if you simply follow all the steps of your troubleshooting process to the letter.  That being said, here are some of the most common diagnostic mistakes people make diagnosing and troubleshooting a P0131.

The most common mistake is not verifying that the P0131 has recurred by clearing all codes and performing a test drive. Sometimes other problems with the engine or fuel system may cause the P0131 to code even if the circuit and sensor are fine.

The second most common mistake is the chicken-or-egg problem of engine misfire. Misfiring can be caused by an oxygen sensor failure, but occasionally the engine misfires have some other cause that results in the problematic oxygen sensor readings. You may have to tinker around a bit and look over the freeze-frame data to find out which problem

Last but not least, a faulty coolant temperature sensor can lead to a misdiagnosis as well. Be certain to check that sensor out before you start replacing O2 sensors or wiring kit.

How serious is this?

Your vehicle is going to run extremely poorly and has a high potential to stall out while running, or it may fail to start on a regular basis. If you see a P0131 code on your OBDII scanner, you need to get the problem diagnosed and corrected as soon as possible to stay safe on the road.

What repairs can fix the code?

Despite one or two rare outliers, there are just a simple repairs to resolve a P0131:

Confirm P0131 is present with a scan tool, here’ a great one that we use daily then clear the fault code and complete a road test ensuring P0131 comes back. Sometimes there is a substance fouling the O2 sensor and it can send faulty readings to the ECM. When the debris blows loose, the sensor functions normally again.

Perform a visual inspection of the bank 1 sensor 1 wiring and replacing or repairing any wiring or connectors found to be faulty.

Check voltage and resistance of bank 1 sensor 1, and replace wiring or connectors as necessary.

Replace the oxygen sensor bank 1 sensor 1 with a new sensor if you have performed all other troubleshooting steps and determined the sensor is faulty.

Related codes

None listed.


A faulty O2 sensor is nothing to mess around with. Whether you can fix this issue yourself or you need to take it to a shop, handle it right away. You don’t want to stall out in the middle of a busy intersection and cause an accident,  or worse, find yourself stranded in a parking lot or along the side of a highway. Prompt diagnosis and repair are critical to keeping your car in good working order.

P0131 Code – What Does It Mean & How To Fix It