Bank 1 Air-Fuel Ratio Imbalance
The fuel-trim values across cylinders on bank 1 differ enough that the bank-average air-fuel ratio is biased — a single cylinder is significantly leaner or richer than the rest. Detected by short-term-fuel-trim variance or by the wide-band O2 sensor harmonic monitor.
Affected components
- Fuel injector
- Oxygen sensor
- Intake manifold
Common causes
- High likelihood: One injector clogged or leaking
- Medium likelihood: Vacuum leak at one intake runner
- Low likelihood: Low compression on one cylinder
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
Related codes
Sources
Diagnostic information is provided for reference only. Confirm the code with a compatible scan tool and follow the vehicle manufacturer's service procedures before replacing components.