System Too Lean Off Idle Bank 1
Fuel trim values on bank 1 indicate a lean condition during off-idle operation. The ECU has to add significant fuel correction to maintain stoichiometric mixture above idle.
Affected components
- Intake manifold
- Vacuum hoses
- Mass air flow sensor
- Fuel pump
- Fuel injector
Common causes
- High likelihood: Vacuum leak under load
- Medium likelihood: Low fuel pressure / weak pump
- Medium likelihood: Contaminated MAF sensor
Possible symptoms
- Check engine light on
- Rough idle, possible stalling
- Hesitation or hard cold start
- Power loss under load
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
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.