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P0031 OBD Fault Code (Causes & Fixes)

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Last Updated on: 7th September 2023, 12:35 am

The P0031 fault code stands for: HO2S Heater Control Circuit Low (Bank 1, Sensor 1)

It’s caused by a low voltage in the bank 1 HO2S1 (pre catalytic converter heated oxygen sensor 1) heating element.

This DTC is minor-moderate in severity, the vehicle can still be driven but should be repaired as soon as feasible.

In this article, we’ll explain what the P0031 OBD fault code means, its signs and causes, and how to fix it.

What Does P0031 Mean?

When the ECU attempts to manage the heater control circuit for Bank 1 Sensor 1 but identifies a low voltage situation, it triggers the P0031 code.

The engine needs an optimal air-fuel ratio of 14.7:1 for proper operation.

To monitor and ensure this air-fuel ratio is met, the HO2S (oxygen sensor) evaluates the oxygen content in the exhaust.

The heating of the oxygen sensor is used to accelerate the response within the closed-loop system, thereby reducing emissions during startup.

If an issue arises with the heating element of the HO2S, resulting in low voltage outside the pre-determined range, it results in the error code P0031.

How Serious Is It?

A P0031 OBD fault code is rated as minor to moderate in severity.

Because the HO2S has a very small influence in how the engine operates, there are usually few drivability issues associated with this code.

Therefore, the vehicle may be driven still, but it should be repaired as soon as possible. Always verify this code is real by using a high-quality OBD scanner.

If this fault code is left unfixed for an extended period of time you may encounter the issues listed below.

  • poor performance
  • lower fuel efficiency
  • sensor loop failure
  • potential damage to other components

Signs & Symptoms

A P0031 fault code may not result in many, or any, noticeable issues. It’s likely to be found by mistake when running an OBD system scan.

However, in some cases you may notice the following:

  • The check engine light may come on
  • Reduced performance and drivability
  • Lower fuel efficiency

Possible Causes

Below are the most common causes of a P0031 trouble code.

  • Faulty heated oxygen sensor
  • Exhaust ground connection that is damaged, corroded or loose
  • Faulty sensors
  • Faulty wiring to the oxygen sensor
  • Water ingress

It’s common for vehicles with over 80,000-100,000 miles to have sensor faults that arise at start-up or during sustained driving.


You should use a compatible and advanced OBD scanner to verify the P0031 code is the issue.

  • Verify if there are any fault codes in addition to the P0031 code.
  • Examine the bank 1 pre catalytic converter oxygen sensor wire for fraying, damage or loose connections.
  • Check for continuity to ground on the ground side of the O2 sensor’s heater circuit. If there is no continuity, repair wiring as needed.
  • With the engine off and the key in the “on” position, use a voltmeter to check the power side of the O2 sensor heater for around 12 volts (the same voltage as the car battery).
  • If no voltage is detected, examine the fuse, if the fuse is fine, consider fixing the short/open circuit in the heater circuit wiring.
  • If low voltage is detected, check the wiring for excessive resistance.
  • If the voltmeter reads 12 volts, replace the heated oxygen sensor.

How to Fix

Check for all possible causes of P0031 and attempt the most likely repairs, then clear the OBD system of fault codes, test drive the vehicle and scan again.

If the code reappears after you’v attempted a fix, try the next repair option.

Common fixes for a P0031 fault code are to:

  1. Reset the code after verifying it using a professional OBD reader. After that, test drive the vehicle to determine whether the issue code has been cleared or if it reappears.
  2. If the code appears, check voltage and ground, then repair or replace any loose or faulty wiring to the HO2S.
  3. If this does not fix the P0031 issue, the HO2S sensor should be replaced.

It typically costs about $200-$300 for a new oxygen sensor and $100-$1000 for the wiring repair/replacement, depending on the issue, your vehicle make/model, and your location.

  • Andy Lewin

    Andy Lewin is a senior mechanic, ASE qualified master technician, and an experienced automotive engineer. He's passionate about serving the automotive community with the highest-quality and trustworthy information on all things automotive. He loves to write about car repairs, maintenance, car modifications and tuning, faults, and much more.

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