The mixture on bank 1 has too much air or too little fuel, and the computer has reached its correction limit. The driver may notice hesitation, rough idle or nothing beyond the engine light.
Likely causes, most common first
- Vacuum leak after the air flow sensor
- Dirty or faulty MAF sensor
- Low fuel pressure
- Exhaust leak before the oxygen sensor
Parts usually involved
- Intake hoses and gaskets
- MAF sensor
- Fuel pump
- Fuel filter
Test before you replace
Compare fuel trims at idle and at 2500 rpm, smoke test the intake and measure fuel pressure.
General guidance for generic OBD2 codes. Always follow the maker's procedure for the car in front of you.