Check the "Possible Causes" listed above. Visually inspect the related wiring harness and connectors. Check for damaged components and look for broken, bent, pushed out, or corroded connector's pins.
If the P0171 is combined with the P0174 code, it's highly likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the Mass Air Flow (MAF) Sensor. If the problem persists the Air Fuel Ratio (A/F) Sensor (Front Oxygen Sensor) may need to be replaced. If the vehicle runs out of fuel, the air-fuel ratio is lean and DTC P0171 may be stored.
There is a factory service bulletin for the following Toyota models:
2005–2007 Toyota Avalon
2007–2008 Toyota Camry
2005-2007 Toyota Avalon, 2007-2008 Toyota Camry Factory Service Bulletin OBDII Code P0171
2005-2006 Toyota Corolla
2005-2006 Toyota Matrix
2005-2006 Toyota Corolla, Matrix Factory Service Bulletin OBDII Code P0171
The cost of diagnosing the P0171 Toyota code is 1.0 hour of labor. The auto repair labor rates vary by location, your vehicle's make and model, and even your engine type. Most auto repairs shops charge between $75 and $150 per hour.
The fuel trim is related to the feedback compensation value, not to the basic injection duration. The fuel trim consists of both short-term and long-term fuel trims.
The short-term fuel trim is fuel compensation that is used to constantly maintain the air-fuel ratio at stoichiometric levels. The signal from the air-fuel ratio sensor indicates whether the air-fuel ratio is rich or lean compared to the stoichiometric ratio. This triggers a reduction in the fuel injection volume if the air-fuel ratio is rich and an increase in the fuel injection volume if lean.
Factors such as individual engine differences, wear over time, and changes in the operating environment cause short-term fuel trim to vary from the central value. The long-term fuel trim, which controls overall fuel compensation, compensates for long-term deviations in the fuel trim from the central value caused by the short-term fuel trim compensation.
Under closed-loop fuel control, fuel injection volumes that deviate from those estimated by the Engine Control Module (ECM) cause changes in the long-term fuel trim compensation value. The long-term fuel trim is adjusted when there are persistent deviations in the short-term fuel trim values. Deviations from the fuel injection volumes estimated by the ECM also affect the average fuel trim learned value, which is a combination of the average short-term fuel trim (fuel feedback compensation value) and the average long-term fuel trim (learned value of the air fuel ratio). If the average fuel trim learned value exceeds the malfunction thresholds, the ECM interprets this as a fault in the fuel system and stores a Diagnostic Trouble Code (DTC).
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