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P0171 TOYOTA

P0171 TOYOTA - Air/Fuel Mixture System Lean Bank 1

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Possible causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection
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Tech notes
If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.

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 Service Bulletin OBDII Code P0171

2005-2006 Toyota Corolla
2005-2006 Toyota Corolla Service Bulletin OBDII Code P0171
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When is the code detected?
- Fuel injection system does not operate properly.
- The amount of mixture ratio compensation is too small. (The mixture ratio is too lean.)
Symptoms
- Engine Light ON (or Service Engine Soon Warning Light)
- Excessive Fuel Consumption
P0171 TOYOTA Description
With the Air/Fuel Mixture Ratio Self-Learning Control, the actual mixture ratio can be brought closely to the theoretical mixture ratio based on the mixture ratio feedback signal from the heated oxygen sensors 1. The Engine Control Module (ECM) calculates the necessary compensation to correct the offset between the actual and the theoretical ratios.
In case the amount of the compensation value is extremely large (The actual mixture ratio is too lean.), the ECM judges the condition as the fuel injection system malfunction and light up the MIL (2 trip detection logic).
TOYOTA Technical Service Bulletins for P0171 code
2000 TOYOTA CELICA ENGINE AND ENGINE COOLING:ENGINE Details
2000 TOYOTA MR2 ENGINE AND ENGINE COOLING:ENGINE Details
2001 TOYOTA CELICA ENGINE AND ENGINE COOLING:ENGINE Details
2001 TOYOTA MR2 ENGINE AND ENGINE COOLING:ENGINE Details
2002 TOYOTA CELICA ENGINE AND ENGINE COOLING:ENGINE Details
2002 TOYOTA MR2 ENGINE AND ENGINE COOLING:ENGINE Details
2003 TOYOTA CELICA ENGINE AND ENGINE COOLING:ENGINE Details
2003 TOYOTA COROLLA ENGINE AND ENGINE COOLING:ENGINE Details
2003 TOYOTA MATRIX ENGINE AND ENGINE COOLING:ENGINE Details
2003 TOYOTA MR2 SPYDER ENGINE AND ENGINE COOLING:ENGINE Details
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