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HOMESERVICE MANUALSCHEVROLET1997CHEVY EXPRESS G3500, VAN CARGO, 6.5 FREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 33 (ENGINE CONTROLS - TESTS W/CODES - 3.8L)TROUBLE CODE CHARTSCODE P0171, FUEL TRIM LEANNOTES
1997 Chevrolet Chevy Express G3500, Van Cargo, 6.5 F

Code P0171, Fuel Trim Lean: Notes

1997 Chevrolet Chevy Express G3500, Van Cargo, 6.5 FSECTION Notes
WARNING: This page is about a different car, the 1995 Pontiac Trans Sport, 1995 Oldsmobile Silhouette, and 1995 Chevrolet Lumina APV. However, it is still accessible from the selected car via links, so may be relevant.

A closed loop air/fuel metering system is used to provide the best possible combination of driveability, fuel economy and emission control. While in closed loop, control module monitors oxygen sensor signal voltage and adjusts fuel delivery based on signal voltage. The Tech 1 monitors fuel trim values, and will indicate a change made to fuel delivery by the long and short term fuel trim values.

Ideal fuel trim values are about 128. If oxygen sensor signal indicates a lean condition, control module will add fuel, resulting in a fuel trim value greater than 128. If a rich condition is detected, fuel trim values will be less than 128, indicating control module is reducing amount of fuel delivered. Control module will set Code P0171 if an excessively lean condition is detected.

NOTE: Test numbers refer to numbers on diagnostic chart.
  1. Visually/physically checking components/systems which may cause a lean condition may determine cause of Code P0171.
  2. MAF sensor which causes control module to read a lower than actual airflow can cause a lean condition, and Code P0171 to set.
  3. Check for faults in EVAP purge system that may cause Code P0171 to set.
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