The upstream oxygen sensor on bank 1 switches too slowly. The driver may see higher consumption with little other change.
Likely causes, most common first
- Aged or contaminated oxygen sensor
- Exhaust leak near the sensor
- Vacuum leak or fuel trim problem
- Wiring fault
Parts usually involved
- Oxygen sensor
- Sensor connector
Test before you replace
Watch the sensor signal live with the engine warm and confirm fuel trims are normal.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.