System Too Rich (Bank 1)
Long-term fuel trim on bank 1 is at the lower limit — the ECU is removing fuel from baseline but mixture remains too rich. Indicates excess fuel delivery, restricted air flow, or a faulty oxygen sensor reporting falsely lean.
Affected components
- Fuel pressure regulator
- Fuel injector
- Air filter
- Oxygen sensor upstream
- Mass air flow sensor
Common causes
- High likelihood: Fuel pressure regulator stuck closed
- Medium likelihood: Leaking fuel injector
- Medium likelihood: Severely blocked air filter
- Low likelihood: Oxygen sensor reporting incorrectly
Possible symptoms
- Check engine light on
- Increased fuel consumption
- Black smoke from exhaust on acceleration
- Smell of unburned fuel, fouled spark plugs
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.