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.
DTC P0171: Fuel System Too Lean: General Description
The engine control module (ECM) detects the oxygen content in the exhaust gas from the air/fuel ratio (A/F) sensor (sensor 1) signal voltage, and it performs fuel feedback control to maintain the optimal air/fuel ratio. The air/fuel ratio coefficient for correcting the amount of injected fuel is the short term fuel trim. The ECM varies short term fuel trim continuously to keep the air/fuel ratio close to the stoichiometric ratio for all driving conditions.
Long term fuel trim is computed from short term fuel trim and is used to regulate long term deviation from the stoichiometric air/fuel ratio, which occurs when fuel metering components deteriorate with age or system failures occur. In addition, long term fuel trim is stored in the ECM memory and is used to determine when fuel metering components malfunction. When long term fuel trim is higher than normal, which is about 1.0 (0 %), the amount of injected fuel must be increased, and when lower than normal, it must be decreased. If long term fuel trim is higher than normal (too lean), a malfunction in the fuel metering components is detected and a DTC is stored.
| Execution | Once per driving cycle(1) | ||
| Sequence | None | ||
| Duration | Every 7 seconds | ||
| DTC Type | Two drive cycles, MIL ON | ||
| OBD Status | N/A | ||
|
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| Condition | Minimum | Maximum |
|---|---|---|
| Engine coolant temperature | 156°F (69°C) | - |
| Intake air temperature | 20°F (-7°C) | - |
| Engine speed | 800 rpm | 4,700 rpm |
| MAP value | 20 kPa (6.0 in.Hg, 150 mmHg) | - |
| Fuel feedback | Closed loop | |
| Monitoring priority | P0420, P0456, P0457, P0497 | |
| No active DTCs | P0107, P0108, P0112, P0113, P0117, P0118, P0134, P0135, P0137, P0138, P0300, P0301, P0302, P0303, P0304, P0335, P0339, P0443, P0496, P1109, P1128, P1129, P1157, P1172, P2195, P2227, P2228, P2229, P2238, P2252, P2270, P2271, P2646, P2647, P2648, P2649 | |
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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.