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P0031 Code – What Does It Mean & How To Fix It

This is one of the most frequent OBD2 trouble codes. Read the full article below to know what it means, how to fix it, and what other codes may show related to it.


Error code due to low voltage of the Bank1 HO2S1 (pre catalytic converter heated oxygen sensor) heating element.


P0031 is an automated generic code that occurs in OBD-II equipped vehicles. The fault P0031 shows up when the engine exhaust does not maintain the air-fuel ratio. The error code is caused by low voltage  of heating element Bank 1 HO2S1. For smoothly running the engine, it is vital to keep the air-fuel ratio of 14.7 to 1. The oxygen sensors are located in Bank 1 near the catalytic converter and at the back end of Bank2. The heated oxygen sensors (HO2S) detect the amount of oxygen and combustion in the car’s exhaust and send direct signals towards the Engine Control Module, generally known as ECM2. The primitive function of ECM is to alter the volume of fuel provided to the car’s engine as per its need. 

When the engine of a car is starting or warming up, it releases carbon. 

HO2S1 is a mechanically calibrated device that sends prompt signals to ECM to control carbon emissions. ECM or the vehicle’s mainframe computer adjusts the changes according to the oxygen content in the air and the air sucked in the engine. The gas sensor stops detecting the air-fuel ratio when your motor vehicle is parked in a cold area or has a low gas temperature. However, to overcome this, heaters are installed with the air-fuel sensor to record precise readings. 

The regular occurrence of the code P0031 refers to the heater circuit that has low resistance as compared to the normal range. 


The fault error P0031 can be indicated due to multiple reasons. After restarting the engine and resetting the code, if the error P0031 still shows up, then there might be a chance that your H02S1 sensor is not transmitting proper signals to the ECM. Some of the most prominent causes are listed below:

  • A flawed or defective heating element in sensors
  • Problems in the 12V battery connections
  • Fault in wirings, connectors, and sensors
  • Malfunctioned PCM/ ECM
  • Accumulated carbon on sensors and plugs


In addition to the lightning malfunction warning light, these prominent indications mentioned below can be observed by the driver when the Code P0031 is disturbing and affecting the car’s engine. 

  • Engine malfunction light will blink
  • ECM detecting low circuits in O2 sensors 
  • The engine system initiates a self mode
  • Malfunctioned heater 
  • Safe mode would produce reoccurring warnings
  • Unless the code is reset, the engine will run in safe mode
  • Low power, insufficient race, and other driving issues


Steps for Self-diagnosis: 

In order to discover the root cause of error code P0031, you need to carry out a detailed inspection of your car’s engine. If the error code P0031 shows up, you must follow the mentioned below steps to diagnose the exact problem:

  • Check whether the heater and 02 sensors are working effectively or not
  • Reset the ECM, and if the error code reappears, check for internal damages in the HO2S1 sensor
  • Search for any burnt and damaged wiring, internal switches, and circuits wired around Bank 1
  • Clean the carbon and soot particles in the engine and heater
  • Use a voltmeter to check whether the 12v battery is operational or dead
  • Check the ground circuit component

Steps for Professional Diagnosis:

 A professionally trained mechanic would start his initial examination by extracting all previous fault codes from the cache memory of the power control module. The mechanic would be using an OBD scanner to scan all error codes and find the root cause. To deduce the problem, the mechanic would follow one of the below-mentioned procedures:

  • The mechanic will reset the OBD-II code and then take a test run to check whether the error code or blinker is popping up. If the error still exists, the mechanic would check the power input and heating sensor. Moreover, he would also inspect the entire wiring loop around the bank 1 circuit. The direct heat from the exhaust and the catalytic converter might damage the wiring, providing current for the sensors. After a detailed inspection, the mechanic can only suggest if any part or circuit requires repairing or changes. 
  • The second method is to conduct a detailed diagnosis using a voltmeter to check for sensor and fuses’ voltage readings. If the mechanic feels that the battery is working perfectly fine, he will remove the entire circuit from ECM and check its resistance.

Common Mistakes

The mechanic or the automobile technician might replace the O2 sensors, but that might not solve the error code P0031 problem. It is wise to check all the wirings and circuit fittings of the 02 sensors. Moreover, the mechanic should ensure that there is 12v delivered to the sensor and the ground. It is essential to check whether the connectors are in place and working.

How Serious is This?

The blinking of engine warning light indicates a malfunction in one of the components of the engine. However, the vehicle can still be driven while it is showing the error code P0031. It is recommended to get your car checked to avoid any technical and mechanical issues such as sensor loop falling, poor operation, and excessive fuel consumption. If you are on a journey and the error code P0031 pops up, you can reset the OBD-II system and continue driving. 

How to Fix This?

Regular maintenance and tuning off the engine will keep your engine running smoothly. It is imperative to get your vehicle checked by certified mechanics to test heat sensors and their efficiency. As a user, you need to ensure that the connectors are in place and free from rust or carbon.

Related Codes

Other codes related to P0031 are P0036, P0037, P0038, and P0520


With timely maintenance and engine tuning, you can enjoy a smooth drive without the error code P0031 popping up. Although P0031 can cause multiple malfunctions and affect the efficiency of a vehicle, regular visits to the mechanic can reduce the chances of uncertain damages to various components of the engine.

P0031 Code – What Does It Mean & How To Fix It