DTC 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 A/F sensor 1. The 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 illuminates the MIL (2 trip detection logic).

Sensor	Input signal to ECM	ECM function	Actuator
A/F sensor 1	Density of oxygen in exhaust gas (Mixture ratio feedback signal)	Direct fuel injection control	Direct fuel injector

DTC DETECTION LOGIC

DTC		CONSULT screen terms(Trouble diagnosis content)	DTC detection condition
P0171	00	FUEL SYS-LEAN-B1(System too lean bank 1)	Diagnosis condition	-
			Signal (terminal)	-
			Threshold	Direct fuel injection system does not operate properly The amount of mixture ratio compensation is too large. (The mixture ratio is too lean.)
			Diagnosis delay time	-

POSSIBLE CAUSE

Intake air leakage
A/F sensor 1
Direct fuel injector
Exhaust gas leakage
Incorrect fuel pressure
Lack of fuel
Mass air flow sensor
Incorrect PCV hose connection

FAIL-SAFE

Engine operating condition in fail-safe mode
Fail safe mode		Vehicle behavior
Traveling control mode	Accelerator angle variation control	ECM controls the accelerator pedal depression speed to make it slower than actual speed. This causes a drop in accelerating performance and encourages the driver to repair malfunction. NOTE: ECM does not control the accelerator pedal releasing speed.
Combustion control mode	Idle speed control	Stops feedback control of idle speed and controls with specified speed.
Combustion control mode	Recovery speed control at decelerating	Stops recovery speed control by the fuel cut at decelerating and controls with specified speed.

DTC CONFIRMATION PROCEDURE

PRECONDITIONING
If DTC Confirmation Procedure has been previously conducted, always perform the following procedure before conducting the next test.

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GO TO 2.
PERFORM DTC CONFIRMATION PROCEDURE-1
1. Clear the mixture ratio self-learning value. Refer to Work Procedure .
2. Start engine.
Is it difficult to start engine?

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GO TO 3.

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GO TO 4.
RESTART ENGINE
If it is difficult to start engine, the fuel injection system has a malfunction, too. Crank engine while depressing accelerator pedal.

NOTE: When depressing accelerator pedal three fourths (3/4) or more, the control system does not start the engine. Do not depress accelerator pedal too much.

Does engine start?

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Proceed to Diagnosis Procedure .

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Check exhaust and intake air leakage visually.
PERFORM DTC CONFIRMATION PROCEDURE-2
1. Keep engine idle for at least 10 minutes.
2. Check 1st trip DTC.
Is 1st trip DTC detected?

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Proceed to Diagnosis Procedure .

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GO TO 5.
PERFORM DTC CONFIRMATION PROCEDURE-3
1. Turn ignition switch OFF and wait at least 10 seconds.
2. Start engine and Maintain the following conditions for at least 10 consecutive minutes. Hold the accelerator pedal as steady as possible.
  
  Vehicle speed 50 - 100 km/h (31 - 62 MPH)
  
  CAUTION:
  Always drive vehicle at a safe speed.
3. Check 1st trip DTC.
Is 1st trip DTC detected?

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Proceed to Diagnosis Procedure .

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To check malfunction symptom before repair: Refer to Intermittent Incident .

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Confirmation after repair: INSPECTION END