P0031
HO2S Heater Control Circuit Low (Bank 1 Sensor 1)
O2 sensor heater control circuit on bank 1, sensor 1 reports low voltage. Likely shorted to ground or open in the heater control wire. The heater warms the sensor element to operating temperature (~600 °C); without it the sensor stays inactive in closed loop and the ECM cannot trim mixture.
- Check engine light: Yes
- Emissions related: Yes
- Repair difficulty: easy
Common causes
Ordered by how often each turns out to be the cause.
- Heater control wire shorted to groundCommon
- Heater element internally shortedPossible
- Connector pins corroded - high contact resistanceLess likely
Parts involved
- Oxygen Sensor Heater
- Sensor Wiring
P0031 is a generic OBD-II code defined by SAE J2012. Exact wording and diagnostic procedure vary by manufacturer and model. Code definitions are drawn from the public-domain OBDex dataset; the workshop notes are our own.