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P1131 code: Meaning, Symptoms, Causes, and Fixes

  • Cars Explained
  • Silas Smith
  • 5 minutes

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OBD2 Code P1131 is one among many trouble codes that point out something is wrong with your car. Unfortunately, most people, especially new drivers, are unaware of these codes produced by the self-diagnostic system of cars. Some of these codes indicate minor troubles, while others if left unattended, can result in bigger issues.


Here you can find answers to questions like what is code P1131, what are the symptoms, and how to fix the issue. Basically, this is a manufacture-specific code commonly found in Ford vehicles. So if you own the Ford Explorer, Ranger, F150, Escort, or the Ford Mustang, there is a chance that you might have encountered code P1131. If not, this article will help you get the necessary information to identify, locate and solve the trouble code P1131.

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What is the Ford P1131 code?

If you own a Ford and the engine code P1131 is displayed, then there is an issue with the O2 sensor. To be precise, if this code comes up, that means the engine is working in a lean condition.

The engine mixes fuel and air, and the O2 sensor calculates the volume of oxygen in the exhaust. The ideal ratio is 1:14.7, which translates as 1 part of the fuel to 14.7 parts of air.

Rich condition: When the ratio is less than 14.7, i.e., there is more fuel than air. The resulting mixture is said to be ‘rich,’ and the engine is now under rich conditions.

Lean condition: In such cases, the ratio is more than 14.7; that is, there is less fuel than air. The fuel-air mixture is ‘lean.’

What are the symptoms of engine code P1131?

Some of the common symptoms of this diagnostic error code include:

  • Check Engine Light turns ON.
  • Car Slow or no acceleration.
  • Failure to start.
  • Bad fuel economy.
  • Engine knocks due to premature combustion.
  • Car Stalls.
  • High gas emissions from the exhaust.

The major consequence of error code P1131 is poor fuel economy and fewer exhaust emissions. However, if there is an ideal fuel-to-air ratio, the engine will stay healthy for a longer period. Also, there will be better fuel economy and less dangerous tailpipe gas emissions.

What are the causes of this trouble code?

You already read that this error code is displayed when there is a lean condition. So what causes a lean condition? Here are a few possibilities.

  • Fuel filter clogs: A block in the fuel filter prevents the fuel from reaching its destination as it does not pass properly after filtration.
  • Fuel injectors malfunction: If the pressure in the injectors is low, there is a chance for a lean mixture. Similarly, leaks or damage in the fuel injectors can also be a problem.
  • Faulty fuel pump: The fuel pump is responsible for transferring fuel to the combustion chamber. This diagnostic code can occur if fuel is not being pumped with optimal pressure.
  • Fuel System trouble: Every fuel system component can be responsible for the P1131 trouble code.


  • Malfunctioning O2 sensor: Since the sensor’s reading is what matters in deciding the occurrence of the error code, a faulty sensor can be the villain.
  • Air leaking into the engine: Physical damage or leaks in the engine can cause air to enter the combustion chamber. This will result in more air than fuel in the mixture.
  • Airflow mass sensor error: The amount of air entering the cylinder is measured by a sensor called Airflow Mass Sensor. Any fault in this device can lead to the P1131 code being displayed.
  • Onboard computer error: Even though the control system is seldom wrong about these errors, there is a small chance the diagnostics system can be faulty. A casual visit from a professional can sort it out within no time.

How do I fix code P1131?

The first step is to make sure there are no other OBD codes. If yes, then diagnose and solve them first before moving on to P1131. Below are the steps for finding and fixing error code P1131.

  • Check for breaks in wiring and connectors of the O2 sensor: You can locate the sensor generally in the exhaust manifold. First, look for damages like melted plastic or bare wires. If the latter is the case, ensure the wires are not grounded. Next, replace the sensor and clear the codes. If the codes return, move on to the next step.
  • Test the Airflow Mass Sensor: In an ideal scenario, the sensor signal sent to the Powertrain Control Module will increase once you start the engine. You can see this using a scan tool. Replace the sensor if the voltage transmitted does not match the ideal voltage.
  • Check for air leaks: A visual check would help you find air leaks in the engine. See if there are any physical damages or holes in the frame or circuitry.

Some other fixes include replacing the fuel filters and injectors and thoroughly checking the fuel pressure sensor and fuel system.

Can I still drive with this error code?

Since the common symptoms include car stalling and poor performance, it is safe to say the car will not run for long. Besides poor fuel economy and low engine output, driving for long distances with this error code can damage the piston.

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