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P0131 Fault Code

You can find information about the P0131 fault code on this page.

It is one of the most popular fault codes that people search for on this website (in the top 50).

We have given it a seriousness of 6/10 with 1 being the least serious and 10 being the worst.

P0131 Short Description

"O2 Sensor Circuit Low Voltage (Bank 1 Sensor 1)"

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Description Icon Long Description

Fault code P0131 is logged when the engine control unit (ECU) has detected an issue with the bank 1 heated oxygen sensor 1 circuit.

A heated oxygen sensor is used to monitor the air-fuel ratio found in the exhaust gases. When too little oxygen is detected, it signals a low voltage output to the ECU. These sensors help determine the level of emissions that are being produced by the engine.

This fault code means that either the air-fuel mixture or the voltage signal from the sensor is incorrect.

Sensor 1 is considered the upstream heated oxygen sensor. Bank 1 refers to the side of the engine where cylinder 1 is located. This is only applicable to V-shape engines.

Manufacturers like Honda, Ford, and Volkswagen are some of the more commonly searched for this issue.

Warnings Icon Other Signs of This Problem

There are usually only a few signs of an issue with a heated oxygen sensor. This makes it important to look out for the presence of the Check Engine light and the subsequent fault codes being logged.

There may be some issues with the performance of the vehicle as the ECU is being fed incorrect information. These can be small things like the engine running mildly rough or a lack of power.

If the emissions are rich enough, there may be some smoke or odor emitted from the exhaust pipes. The term ‘rich’ is used to describe an engine that is using too much fuel and too little air at a given time.

There may be other codes like P0131 that can indicate the engine is running rich.

Be sure to look for other heated oxygen sensor codes like P0135, P0137, and others.

Broken Down Icon What Could Be The Problem?

There are several common causes for issues with heated oxygen sensors. These can relate to the oxygen sensor and its wiring or the actual issue the sensor is picking up.

In the case of the sensor, it is possible the sensor is faulty or its wiring and connections are damaged or loose.

Additionally, it is possible that there is an open or short in the heated oxygen sensor circuit.

A leak upstream of the heated oxygen sensor can also result in a low-voltage output signal being detected.

In rare instances, the issue might be a faulty ECU or outdated software.

If the engine is actually running lean, it may be an issue with the mass airflow sensor (MAF). This can also happen as a result of a clogged fuel filter or faulty fuel pump.

Fixed Icon Fixes

Fixes include repairing any leaks in the exhaust system or replacing faulty parts.

If the heated oxygen sensor is faulty, it should be replaced. This can be done by checking the resistance and voltage of the sensor.

Be sure to check all of the corresponding wiring and connections for damage or looseness as a quick fix for the P0131 fault code.

Any leaks in the exhaust should be fixed.

If the engine is running rich, this must be fixed as well. Ensure the fuel injectors, fuel pump, and fuel pressure regulator are all in working order. Also, ensure the fuel filter is also not clogged. Replace any of these parts if they are not functioning properly.

If the ECU is faulty, it must be replaced. Software updates can also help here.

Danger Icon Seriousness

Fault code P0131 should be considered a moderately serious issue. In some instances, this code can result in damage to the catalytic converter, which can be an expensive fix.

It is best to have this issue fixed as soon as possible.

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