Infiniti QX56 (Z62). Manual - part 571

EC-262

< DTC/CIRCUIT DIAGNOSIS >

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P0139, P0159 HO2S2

6.

REPLACE HEATED OXYGEN SENSOR 2

Replace malfunctioning heated oxygen sensor 2. Refer to 

EM-40, "Exploded View"

.

CAUTION:

• Discard any heated oxygen sensor which has been dropped from a height of more than 0.5 m (19.7

in) onto a hard surface such as a concrete floor; use a new one.

• Before installing new oxygen sensor, clean exhaust system threads using Oxygen Sensor Thread

Cleaner [commercial service tool (J-43897-18 or J-43897-12)] and approved anti-seize lubricant
(commercial service tool).

>> INSPECTION END

P0171, P0174 FUEL INJECTION SYSTEM FUNCTION

EC-263

< DTC/CIRCUIT DIAGNOSIS >

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P0171, P0174 FUEL INJECTION SYSTEM FUNCTION

DTC Logic

INFOID:0000000006217825

DTC DETECTION LOGIC

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).

DTC CONFIRMATION PROCEDURE

1.

PRECONDITIONING

1.

Turn ignition switch OFF and wait at least 10 seconds.

2.

Turn ignition switch ON.

3.

Turn ignition switch OFF and wait at least 10 seconds.

>> GO TO 2.

2.

PERFORM DTC CONFIRMATION PROCEDURE-I

1.

Clear the mixture ratio self-learning value. Refer to 

EC-152, "Work Procedure"

.

2.

Start engine.

Is it difficult to start engine?

YES

>> GO TO 3.

NO

>> GO TO 4.

3.

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?

YES

>> Proceed to 

EC-264, "Diagnosis Procedure"

.

NO

>> Check exhaust and intake air leakage visually.

4.

PERFORM DTC CONFIRMATION PROCEDURE-II

1.

Keep engine idle for at least 5 minutes.

2.

Check 1st trip DTC.

Is 1st trip DTC detected?

YES

>> Proceed to 

EC-264, "Diagnosis Procedure"

.

Sensor

Input signal to ECM

ECM function

Actuator

A/F sensor 1

Density of oxygen in exhaust gas
(Mixture ratio feedback signal)

Fuel injection control

Fuel injector

DTC No.

Trouble diagnosis name

(Trouble diagnosis content)

DTC detecting condition

Possible cause

P0171

FUEL SYS-LEAN-B1
[Fuel injection system too 
lean (bank 1)]

• Fuel injection system does not operate properly.
• The amount of mixture ratio compensation is too 

large. (The mixture ratio is too lean.)

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

P0174

FUEL SYS-LEAN-B2
[Fuel injection system too 
lean (bank 2)]

EC-264

< DTC/CIRCUIT DIAGNOSIS >

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P0171, P0174 FUEL INJECTION SYSTEM FUNCTION

NO

>> GO TO 5.

5.

PERFORM DTC CONFIRMATION PROCEDURE-III

1.

Turn ignition switch OFF and wait at least 10 seconds.

2.

Turn ignition switch ON.

3.

Turn ignition switch OFF and wait at least 10 seconds.

4.

Start engine.

5.

Maintain the following conditions for at least 10 consecutive minutes. 
Hold the accelerator pedal as steady as possible.

CAUTION:

Always drive vehicle at a safe speed.

6.

Check 1st trip DTC.

Is 1st trip DTC detected?

YES

>> Proceed to 

EC-264, "Diagnosis Procedure"

.

NO

>> INSPECTION END

Diagnosis Procedure

INFOID:0000000006217826

1.

CHECK EXHAUST GAS LEAKAGE

1.

Start engine and run it at idle.

2.

Listen for an exhaust gas leakage before three way catalyst (manifold).

Is exhaust gas leakage detected?

YES

>> Repair or replace malfunctioning part.

NO

>> GO TO 2.

2.

CHECK FOR INTAKE AIR LEAKAGE

1.

Listen for an intake air leakage after the mass air flow sensor.

2.

Check PCV hose connection.

Is intake air leakage detected?

YES

>> Repair or replace malfunctioning part.

NO

>> GO TO 3.

3.

CHECK A/F SENSOR 1 CIRCUIT

1.

Turn ignition switch OFF.

2.

Disconnect corresponding A/F sensor 1 harness connector.

3.

Disconnect ECM harness connector.

4.

Check the continuity between A/F sensor 1 harness connector and ECM harness connector.

Vehicle speed

50 - 120 km/h (31 - 75 MPH)

PBIB1216E

P0171, P0174 FUEL INJECTION SYSTEM FUNCTION

EC-265

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5.

Check the continuity between A/F sensor 1 harness connector and ground, or ECM harness connector
and ground.

6.

Also check harness for short to power.

Is the inspection result normal?

YES

>> GO TO 4.

NO

>> Repair open circuit, short to ground or short to power in harness or connectors.

4.

CHECK FUEL PRESSURE

Check fuel pressure. Refer to 

EC-153, "Work Procedure"

.

Is the inspection result normal?

YES

>> GO TO 6.

NO

>> GO TO 5.

5.

 DETECT MALFUNCTIONING PART

Check fuel hoses and fuel tubes for clogging.

Is the inspection result normal?

YES

>> Replace “fuel filter and fuel pump assembly”. Refer to 

FL-5, "Removal and Installation"

.

NO

>> Repair or replace malfunctioning part.

6.

CHECK MASS AIR FLOW SENSOR

 WITH CONSULT-III

1.

Install all removed parts.

2.

Check “MASS AIR FLOW” in “DATA MONITOR” mode with CONSULT-III.
For specification, refer to 

EC-538, "Mass Air Flow Sensor"

.

 WITH GST

1.

Install all removed parts.

2.

Check mass air flow sensor signal in Service $01 with GST.
For specification, refer to 

EC-538, "Mass Air Flow Sensor"

.

Is the measurement value within the specification?

YES

>> GO TO 7.

NO

>> Check connectors for rusted terminals or loose connections in the mass air flow sensor circuit or

grounds. Refer to 

EC-201, "Diagnosis Procedure"

.

7.

CHECK FUNCTION OF FUEL INJECTOR

DTC

A/F sensor 1

ECM

Continuity

Bank

Connector

Terminal

Connector

Terminal

P0171

1

F67

3

F110

88

Existed

4

90

6

94

P0174

2

F68

3

78

4

80

6

74

DTC

A/F sensor 1

ECM

Continuity

Continuity

Bank

Connector

Terminal

Connector

Terminal

P0171

1

F67

3

F110

88

Existed

Not existed

4

90

6

94

P0174

2

F68

3

78

4

80

6

74