P0131 OBD-II Trouble Code: O2 Sensor Circuit Low Voltage Bank 1 Sensor 1

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P0131 code definition

The P0131 code is low sensor voltage for oxygen sensor bank 1 sensor 1 or improper air fuel ratio.

What the P0131 code means

P0131 is telling us there is a fault in the oxygen sensor, located in the bank 1 sensor 1 location of the vehicle. This is also called air/fuel sensor, or heated O2 sensor. This means that the ECU has detected either improper voltage from the oxygen sensor or improper air-fuel ratio.

Bank 1 is referring to the left side of the engine, when sitting in the drivers seat. Sensor 1 is referring to the sensor located before the catalytic converter in the exhaust system.

What causes the P0131 code?

P0131 can be caused by a variety of issues:

  • Failed Oxygen sensor
  • Damage or unplugged wiring
  • Open or short
  • Improperly reading coolant temp sensor
  • Failed heater circuit for oxygen sensor
  • Most commonly the sensor has simply failed due to age and wear

What are the symptoms of the P0131 code?

When a fault is detected in the oxygen sensor circuit the Check Engine Light is illuminated and will be visible on the dashboard. After the Check Engine Light is visible the car’s ECU puts the car into a failsafe mode, sets the air-fuel ration to a fixed condition, and leans the vehicle to prevent catalytic converter damage. Lean conditions may cause poor fuel economy to be observed.

The vehicle may run poorly or stutter when driving with a oxygen sensor issue. In extreme cases the vehicle’s engine may die while running with this code present.

How does a mechanic diagnose the P0131 code?

The first thing any mechanic will do is plug in a OBD2 scanner into the DLC connector, typically located under the dash on the driver’s side, to read and confirm any codes present. With any code there will be an associated freeze frame data which tells us under what conditions such as engine speed, driving speed, run time, engine temperature that the code was set at so we can recreate this in our test drive.

Once P0131 is confirmed, a qualified mechanic will clear the code and take the vehicle on a test drive while observing the vehicles datastreme which will show the oxygen sensor voltage and resistance. If the code comes back on, excessive resistance is shown, or out of range voltage is present the technician has confirmed there is a fault in the oxygen sensor circuit.

The first thing a qualified technician will perform a visual inspection to insure the integrity of the oxygen sensor wiring.

If the wiring is found to be okay the mechanic will check the sensor voltage and resistance. Voltage should be below 1 volt and resistance below manufactures specifications for each vehicle.

Common mistakes when diagnosing the P0131 code

  • The most common mistake is not confirming that a fault is present in the oxygen sensor circuit by clearing the code and performing a test drive.

  • Another common mistake is that engine misfires can be caused by a oxygen sensor failure and alternatively engine misfires can cause the vehicle’s oxygen sensors to read improperly.

  • In addition, a faulty coolant temp sensor can lead to misdiagnoses as well.

How serious is the P0131 code?

A P0131 code can indicate a serious problem that can cause the vehicle to run poorly and die while running. Caution should be observed when this code is present and it should be fixed promptly.

What repairs can fix the P0131 code?

  • Confirm P0131 is present with a scan tool. Clear the fault code and complete a road test ensuring P0131 comes back.

  • Perform a visual inspection of the bank 1 sensor 1 wiring replacing or repairing any wiring that is found to be faulty.

  • Check voltage and resistance of bank 1 sensor 1

  • If necessary replace the oxygen sensor bank 1 sensor 1 with a new sensor.

Additional comments for consideration regarding the P0131 code

Oxygen sensors are made to last the lifetime of the vehicle, but it is not uncommon to have oxygen sensor issues as the vehicle ages and exceeds 100,000 miles.

With this code causing drivability issues, poor fuel economy, and potential engine damage this code should be taken care of as soon as possible.

Need help with a P0131 code?

YourMechanic offers certified mobile mechanics who will come to your home or office to diagnose and repair your vehicle. Get a quote and book an appointment online or speak to a service advisor at 1-800-701-6230.

The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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