Fuel Trim Malfunction (Bank 1)
The ECU detects that short-term and long-term fuel trim values on bank 1 are outside acceptable limits. Engine cannot maintain stoichiometric mixture — typically a vacuum leak, fuel pressure issue, or failing MAF/O2 sensor.
Affected components
- Intake system
- Fuel pressure regulator
- Mass air flow sensor
- Oxygen sensor b1s1
Common causes
- High likelihood: Vacuum leak (intake gasket, hose, PCV)
- Medium likelihood: Fuel pressure too low or too high
- Medium likelihood: MAF sensor reading drifted
Diagnostic notes
- The malfunction indicator lamp may illuminate
- This code can affect emissions
- A drive cycle may be required after repair
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.