The upstream oxygen sensor on bank 1 reads low voltage for too long. The driver may notice poor running or higher consumption.
Likely causes, most common first
- Real lean mixture or vacuum leak
- Exhaust leak near the sensor
- Faulty oxygen sensor
- Short in the sensor wiring
Parts usually involved
- Oxygen sensor
- Sensor connector
- Intake gaskets
Test before you replace
Check fuel trims and exhaust leaks, then test the sensor signal and wiring.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.