Code P0031 OBD2 refers to the Oxygen Sensor (O2) located in bank number 1, in the front of the Catalytic Converter. It should be noted that the Oxygen Sensor (O2) that goes behind the Catalytic Converter is number 2.
The function of both sensors is to detect the amount of oxygen in the exhaust gas to compare it with the outside air. All this in order to achieve an ideal fuel or stoichiometric air / fuel mixture, for this the Powertrain Control Module (PCM) adjusts the air / fuel ratio entering the engine.
Its performance is affected when the temperature of the exhaust gases low, for that reason they are equipped with a heating element, which, when activated, helps to make the readings of the Oxygen Sensor (O2) are the most correct.
Basically, diagnostic code P0031 is established when the Powertrain Control Module (PCM) has detected that the resistance of the heating element circuit is below the expected level. Generally, that level of resistance should be below 0.8 amps.