System Too Lean at Higher Load (Bank 1)
Bank 1 fuel trim hits the lean limit only at higher engine load. Pattern points to a fuel-supply restriction — failing fuel pump, blocked filter, or weak injectors — rather than a vacuum leak (which would dominate at idle).
Affected components
- Fuel pump
- Fuel filter
- Fuel injector
- Mass air flow sensor
Common causes
- High likelihood: Fuel pump weak under load
- Medium likelihood: Fuel filter clogged
- Medium likelihood: MAF reads low at high airflow
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.