P0031 Fault Code

Long Description

Fault code P0031 is logged when the engine control unit (ECU) has detected a malfunction with the bank 1 oxygen sensor 1 circuit. This fault code relates specifically to the upstream heated oxygen sensor circuit.

The upstream heated oxygen sensor is found in the exhaust line before the catalytic converter.

Heated oxygen sensors have internal heater systems to allow them to reach operating temperatures quickly as they monitor oxygen in the hotter exhaust system. These sensors send information to the ECU to determine the emission levels in the exhaust fumes.

This is done to optimize the engine and reduce the total emission levels of the vehicle.

Bank 1 refers to the side of the engine in which cylinder 1 is located. This only applies to V-shaped engines. Inline engines only have a single bank. For the mirror code, see P0051.

Various manufacturers like Kia, Mazda, Suzuki, and Toyota are commonly associated with this fault code.

Other Signs of This Problem

There can be relatively few signs of an issue with the upstream heated oxygen sensor. This means it is important to check the fault codes as soon as notice the following symptoms.

The most obvious sign will be the presence of the Check Engine light on the dashboard – then this P0031 code appears on your OBD2 reader.

Fuel economy can also be reduced as a result of bad signals being sent to the ECU.

This can also come in the form of the engine running roughly.

There may also be other fault codes logged for the heated oxygen sensor. These can be P0030 and P0032 among others.

What Could Be The Problem?

Because the issue is most likely found within the heated oxygen sensor circuit itself, the potential causes will typically be electrical in nature.

These can include a faulty heated oxygen sensor.

Faulty connections or frayed wiring can be the cause. Additionally, loose or corroded connections can result in this issue.

Another possibility is a blown fuse in the heated oxygen sensor circuit.

In rare cases, the powertrain control module (PCM) could be faulty or running on outdated software.

Fixes

Again, most of the fixes for this fault code will be electrical in nature.

If there are any faults in the heated oxygen sensor circuit like damaged wires or loose connections, these need to be fixed.

A blown heated oxygen sensor fuse should also be checked. If it is blown or faulty, it should be replaced.

If these issues are not present, the heated oxygen sensor should be checked. If it is faulty or damaged, it needs to be replaced.

If none of these other issues can be detected, the PCM should be checked. Software updates may be available.

While unlikely, it is possible that the PCM may need to be replaced.

Seriousness

Fault code P0031 should be considered low in terms of seriousness. It does not pose any serious issue to the vehicle or driveability. In some cases, the catalytic converter can be at risk, which can be an expensive fix.

It is a good idea to have this fixed within a few weeks.