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.
Failure Conditions (Long-Term Fuel Trim)
ECM will set a DTC and MIL will illuminate if long-term multiplicative value is less than 77 percent for 30 seconds (for P0171) or if long-term fuel trim value goes to 10-15 percent lean (for P0172) for 30 seconds during 2 driving cycles when following conditions are met:
- Engine load exceeds 1.8 milliseconds.
- ECM is in close loop operation (for P0171).
- Engine coolant temperature is more than 158°F (70°C).
- EVAP canister purge system is not operating.
- Mass airflow is 5.5 grams per second or less.
- Engine speed is below 1000 RPM (for P0172).
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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.