P0170 — 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.
General code reference. Confirm the definition and diagnostic procedure for your vehicle's year, model and engine. A stored code alone does not identify a failed part.
Affected components
- Intake system
- Fuel pressure regulator
- Mass air flow sensor
- Oxygen sensor b1s1
Possible causes to check
These are possible checks, not a ranked diagnosis. Follow the vehicle manufacturer's test procedure before replacing parts.
- Vacuum leak (intake gasket, hose, PCV)
- Fuel pressure too low or too high
- 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
Check each reference's vehicle and model-year scope. General background links do not establish which fault is most likely on your vehicle.
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.