Safety Warning
DIY auto repair can cause serious injury, fire, or vehicle damage. These guides are for informational purposes only. Always follow OEM torque specs, wear PPE, and consult a certified mechanic if you are unsure. You are solely responsible for your safety.
Code P0171, Fuel Trim Lean - "S" & "T" Series 4.3L (VIN W) Bank 1, Sensor 1: Notes
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. 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 if an excessively lean condition is detected.
- Visually/physically checking components/systems which may cause a lean condition may determine cause of code.
- Checks for proper fuel delivery system operation.
- Check for faults in EVAP purge system that may cause Code to set.
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When to See a Mechanic
Stop DIY work and contact a certified mechanic immediately if any of the following apply:
- • You smell fuel, burning insulation, or see smoke.
- • Brakes feel soft, pull hard to one side, or make grinding noises.
- • The engine overheats, stalls repeatedly, or misfires under load.
- • You are missing required tools, torque specs, or safe lifting equipment.
- • You are not confident in the next step or safety outcome.
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