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.
Short Term Fuel Trim
The Short Term fuel trim values change rapidly in response to the heated oxygen sensor (HO2S) signal voltages. These changes fine tune the engine fueling. The ideal fuel trim values are around 0 percent. A positive fuel trim value indicates that the powertrain control module (PCM) is adding fuel in order to compensate for a lean condition. A negative fuel trim value indicates that the PCM is reducing the amount of fuel in order to compensate for a rich condition.
When the PCM determines that the Short Term fuel trim is out of the operating range, the following DTCs will set:
- DTC P0171 Bank 1 Too Lean
- DTC P0172 Bank 1 Too Rich
- DTC P0174 Bank 2 Too Lean
- DTC P0175 Bank 2 Too Rich
NO RELATED
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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.