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P0031 Fault Code (Causes & Fixes) HO2S Heater Control Circuit Low

Updated: Feb 4

✔ This article has been fact checked.

The P0031 code is caused by a low voltage in the bank 1 HO2S1 (pre catalytic converter heated oxygen sensor) heating element.

If a DTC is associated to the powertrain, an OBD scanner will read it as starting with P, thus the letter "P". Generic fault codes are those of the format P0xxx.

Table of Contents:

The Meaning of a P0031 Fault Code

Heated O2 sensors contain a separate heater within the sensor to quickly reach operational temperature.

The quicker your O2 sensors reach working temperature, the sooner your car is in a fuel-efficient and emission-friendly state. The oxygen sensor heater is not operational if this code is set.

When there is a problem with the HO2S heating element, the error code P0031 appears.

Is It Serious?

This error number will not stop your car from functioning. Lower fuel efficiency and poor vehicle operation are the most common issues. However, if this issue is not resolved, it may increase the probability of your car running rough and causing harm to other components.

As a result, the car may be driven, but it should be brought in for diagnostic tests and repair as soon as possible to avoid potential issues such as the following.

  • poor performance

  • lower fuel efficiency

  • sensor loop failure

  • damage to other components

Signs & Symptom

While there may be various indications and signs associated with an OBD-II fault code triggering in many cases, this is not the case with the P0031. Unless you scan the car, there may be few signs.

However, you may notice the following signs:

  • Check engine light (CEL) illumination

  • Poor performance and drivability

  • Lower fuel efficiency

Possible Causes

There are numerous possible causes for the P0031 trouble code, but the following are the most common.

  • Faulty heated oxygen sensor

  • Faulty or blown heater circuit fuse

  • Damaged heater circuit wiring or connectors

  • Malfunctioning PCM / ECM

Diagnosing the P0031 Trouble Code

A professional OBD scanner or a diagnostic check with a knowledgeable technician are the best ways to diagnose a problem code.

Try resetting the code before any diagnostic tests, this may solve the issue. Many vehicles with over 80,000-100,000 miles have sensor faults that arise during start-up or sustained driving.

  1. Clear your Check Engine Light and verify if there are any additional codes in addition to the P0031 code.

  2. Examine the bank 1 pre catalytic converter oxygen sensor wire for fraying, damage or disconnection.

  3. Check for continuity to ground on the ground side of the O2 sensor's heater circuit. If there is no continuity, the wiring should be repaired.

  4. With the engine off and the key "on," use a voltmeter to check the power side of the O2 sensor heater for around 12 volts (this should be the same voltage as the car battery).

  5. If no voltage is detected, examine the fuse; if the fuse is in good working order, consider fixing the short/open in the heater circuit wiring.

  6. If low voltage is detected, inspect the wiring for excessive resistance.

  7. If the voltmeter reads 12 volts, replace the heated oxygen sensor.

Possible Fixes for a P0031 Code

It is recommended that you test drive the vehicle after each repair to see whether the fault code has been resolved. If the error code reappears, go to the next repair option.

Try the following fixes for a P0031 error code:

  1. Reset the trouble code after verifying the code using a professional OBD reader. After that, do a test drive to see whether the error code has been erased completely.

  2. If the code appears, check voltage and ground and repair or replace any loose or faulty wiring to the HO2S.

  3. If this does not fix the problem, the HO2S should be replaced.

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


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