P0171 TOYOTA

P0171 TOYOTA - Air/Fuel Mixture System Lean Bank 1

Repair Importance Level: 3/3

Repair Difficulty Level: 3/3

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

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 replace the air filter and clean the air flow meter. If the problem persists 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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What does this mean?

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.)

Possible 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).

OBDII Code P0171 Toyota - Air/Fuel Mixture System Lean Bank 1 - AutoCodes.com

P0171 Toyota Information for specific Toyota models

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