P0131 – O2 Sensor Circuit Low Voltage

The P0131 code triggers when the voltage output of your upstream bank 1 oxygen sensor is too low. Your engine computer uses this sensor to control the air to fuel ratio. Since maintaining the correct rate is key to proper engine operation, you should note when this trouble code activates.

Fixing the P0131 OBD2 code may require replacing the oxygen sensor, but damaged wires and hoses can also cause it. A thorough diagnosis is essential to find and address the true root of the problem. Read on below for more details about this code and what to do if it’s active.

P0131 Code Definition (Generic)

Oxygen O2 sensor circuit low voltage (Bank 1, Sensor 1)

Here's where you can get a thorough understanding of the P0131 OBD2 code
If you want to learn about the P0131 OBD2 code, this is the right place

What Does P0131 Mean?

The oxygen sensors in your engine are how the power control module (PCM) or engine control module (ECM) monitors the air-to-fuel ratio in your exhaust. Comparing this data with the air outside the engine can determine when to inject more fuel or open the system to allow more air to enter.

There are two oxygen sensors in the vehicle. The upstream oxygen sensor, called sensor 1, is positioned before the catalytic converter. It is different from the downstream oxygen sensor, called sensor 2, which measures the air coming out of the catalytic converter. 

The P0131 trouble code triggers when the ECM or PCM detects a low voltage from the upstream oxygen sensor. Usually, the voltage must be below the threshold for a certain length of time before the code will trigger. Typically this is two minutes, but it can vary depending on your vehicle. 

While P0131 is a generic trouble code, applying to all OBD2 vehicles, the specific fixes can vary depending on your make and model. It’s always a good idea to consult your manual and check for any technical service bulletins before beginning your diagnosis and repair.

Other diagnostic trouble codes related to the oxygen sensors include P0136 and P0137. These codes also warn of a low oxygen sensor voltage, although for a different sensor. 

What Are The Symptoms Of The P0131 Code?

In some cases, there are no drivability issues with the P0131 trouble code. This case is relatively rare, however. Typically, you’ll experience one or more of the following symptoms:

  • Activation of the check engine light
  • Smoke in the exhaust
  • Bad smell from the exhaust
  • Rough running engine
  • Reduced fuel economy
  • Stalling engine

What Are The Causes Of P0131?

  • Faulty or damaged oxygen sensor heating circuit
  • Defective oxygen sensor
  • Faulty or damaged wiring around the oxygen sensor
  • Shorts, open, or high resistance in the oxygen sensor signal circuit
  • Leaks in the vacuum system
  • Fuel pressure too low or too high
  • ECM or PCM software requires an update
  • Faulty ECM or PCM (not as common)

How Serious Is The P0131 Code?

While the severity of the P0131 code can vary, it can be of high severity. Therefore, you should stop driving your vehicle as soon as possible and identify the root of the problem. Failure to do so could lead to more serious engine damage.

How To Diagnose And Fix The P0131 Code?

The P0131 code can be diagnosed by digital multimeter
Digital multimeter is one of the tools which can diagnose the error P0131 code.

Tools you’ll need:

  1. Use an OBD2 scan tool to check for other trouble codes, then clear codes and test drive your vehicle to see if the code recurs. In some cases, P0131 is an intermittent problem. Especially if you haven’t experienced any drivability symptoms, the code may clear without issue.
  2. Read the freeze frame data for oxygen sensor 1. Pay attention to the miles per hour (MPH), revolutions per minute (RPM), and load readings. Also, read the engine temperature sensor readings and the oxygen sensor 2 readings to look for any inconsistencies. 
  3. Visually inspect the wiring around the oxygen sensor. Replace any wires that are damaged or corroded, and check the connectors for damage, as well. Ensure all the wires are firmly connected and clear of any other engine components that could cause future damage. 
  4. Inspect the wiring harness. Perform a wiggle test to make sure it’s not chafing or grounding.
  5. Check the vacuum hoses around the bank 1 upstream oxygen sensor for leaks. Make sure to feel along with hidden areas of the hoses for damaged or weak spots you can’t see. Pay close attention to the ends of the hoses, as well, making sure there’s no fraying or damage and that all hoses are secured tightly. 
  6. Use a digital multimeter to check the voltage output of oxygen sensor 1 on bank 1. Your vehicle’s manual can tell you what the voltage reading should be. If it’s giving a null or infinite reading, you likely have an open or short in the oxygen sensor. Any variance from the designated range is a sign your oxygen sensor probably needs to be replaced. 
  7. Check the signal wire at the PCM or ECM using the digital multimeter. Check for shorts and open circuits, and replace the connector or wire as necessary.
  8. If the code still doesn’t clear, you may need a software update or have a more significant electrical issue. In either case, your best option is to take your vehicle to a professional mechanic for further diagnosis.

Common Mistakes To Avoid While Diagnosing The P0131 Code

Many people replace the oxygen sensor before they search for other potential causes for the trouble code. While a defective oxygen sensor may be the issue, make sure you check for wiring issues and vacuum leaks, as well. These are equally likely to trigger the P0131 trouble code. 

Tips To Avoid P0131 In The Future

Two potential causes of the P0131 trouble code are damaged or loosened wires and vacuum leaks in the exhaust system. You can avoid both through preventative maintenance. Consider applying an anti-corrosive treatment to your engine. Also, be careful when installing hoses and wires. Make sure they’re firmly connected and that they’re not rubbing engine components that could damage them.

Read more: P0135 Code: Meaning, Symptoms, Causes, Diagnostics, and Fixes