System too lean — bank 1

What the code means

Closed-loop fuel correction reached a calibrated lean threshold on bank 1.

Severity and driving

Service soon; urgent with misfire or power loss

Plausible causes

Unmetered intake air
Low fuel delivery
Exhaust leak near sensor
Biased airflow or oxygen-sensor signal

Next checks

Record short- and long-term fuel trim at idle and raised RPM
Inspect only visible intake hoses with engine off
Check related misfire or airflow codes

Source and boundary

Code structure follows SAE J2012. Manufacturer-specific definitions, pinpoint tests, wiring, torque, fluids, and repair procedures require authoritative information for the exact vehicle.

SAE J2012 Diagnostic Trouble Code DefinitionsReviewed 2026-08-13

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