Nissan Xterra. Manual - part 255

EC-146

< DTC/CIRCUIT DIAGNOSIS >

[VQ40DE]

TROUBLE DIAGNOSIS - SPECIFICATION VALUE

OK or NG

OK

>> INSPECTION END

NG

>> GO TO 15.

15.

DISCONNECT AND RECONNECT ECM HARNESS CONNECTOR

1. Stop the engine.

2. Disconnect ECM harness connector. Check pin terminal and connector for damage, and then reconnect it.

>> GO TO 16.

16.

CHECK “A/F ALPHA-B1”, “A/F ALPHA-B2”

1. Start engine.

2. Select “A/F ALPHA-B1”, “A/F ALPHA-B2” in “SPEC” of “DATA MONITOR” mode, and check that each

indication is within the SP value.

OK or NG

OK

>> INSPECTION END

NG

>> Detect malfunctioning part according to 

EC-489, "Symptom Matrix Chart"

.

17.

CHECK “B/FUEL SCHDL”

Select “B/FUEL SCHDL” in “SPEC” of “DATA MONITOR” mode, and check that the indication is within the SP

value.
OK or NG

OK

>> INSPECTION END

NG (More than the SP value)>>GO TO 18.

NG (Less than the SP value)>>GO TO 25.

18.

DETECT MALFUNCTIONING PART

1. Check for the cause of large engine friction. Refer to the following.

-

Engine oil level is too high

-

Engine oil viscosity

-

Belt tension of power steering, alternator, A/C compressor, etc. is excessive

-

Noise from engine

-

Noise from transmission, etc.

2. Check for the cause of insufficient combustion. Refer to the following.

-

Valve clearance malfunction

-

Intake valve timing control function malfunction

-

Camshaft sprocket installation malfunction, etc.

>> Repair or replace malfunctioning part, and then GO TO 30.

19.

CHECK INTAKE SYSTEM

Check for the cause of uneven air flow through mass air flow sensor. Refer to the following.

• Crushed air ducts

• Malfunctioning seal of air cleaner element

• Uneven dirt of air cleaner element

• Improper specification of intake air system
OK or NG

OK

>> GO TO 21.

NG

>> Repair or replace malfunctioning part, and then GO TO 20.

20.

CHECK “A/F ALPHA-B1”, “A/F ALPHA-B2”, AND “B/FUEL SCHDL”

Select “A/F ALPHA-B1”, “A/F ALPHA-B2”, and “B/FUEL SCHDL” in “SPEC” of “DATA MONITOR” mode, and

check that each indication is within the SP value.
OK or NG

OK

>> INSPECTION END

NG (“B/FUEL SCHDL” is more, “A/F ALPHA-B1”, “A/F ALPHA-B2” are less than the SP value)>>GO TO 21.

21.

DISCONNECT AND RECONNECT MASS AIR FLOW SENSOR HARNESS CONNECTOR

TROUBLE DIAGNOSIS - SPECIFICATION VALUE

EC-147

< DTC/CIRCUIT DIAGNOSIS >

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1. Stop the engine.

2. Disconnect mass air flow sensor harness connector. Check pin terminal and connector for damage and

then reconnect it again.

>> GO TO 22.

22.

CHECK “A/F ALPHA-B1”, “A/F ALPHA-B2”

1. Start engine.

2. Select “A/F ALPHA-B1”, “A/F ALPHA-B2” in “SPEC” of “DATA MONITOR” mode, and check that each

indication is within the SP value.

OK or NG

OK

>> 1. Detect malfunctioning part of mass air flow sensor circuit and repair it. Refer to 

EC-172

.

2. GO TO 29.

NG

>> GO TO 23.

23.

CHECK “MAS A/F SE-B1”

Select “MAS A/F SE-B1” in “SPEC” of “DATA MONITOR” mode, and check that the indication is within the SP

value.
OK or NG

OK

>> GO TO 24.

NG (More than the SP value)>>Replace  mass  air flow sensor, and then GO TO 29. Refer to 

EM-24,

"Exploded View"

.

24.

REPLACE ECM

CAUTION:

Perform Additional Service When Replacing ECM. Refer to 

EC-122, "Additional Service When Replac-

ing ECM"

.

Replace ECM.

>> GO TO 29.

25.

CHECK INTAKE SYSTEM

Check for the cause of uneven air flow through mass air flow sensor. Refer to the following.

• Crushed air ducts

• Malfunctioning seal in air cleaner element

• Uneven dirt in air cleaner element

• Improper specification in intake air system
OK or NG

OK

>> GO TO 27.

NG

>> Repair or replace malfunctioning part, and then GO TO 26.

26.

CHECK “B/FUEL SCHDL”

Select “B/FUEL SCHDL” in “SPEC” of “DATA MONITOR” mode, and check that the indication is within the SP

value.
OK or NG

OK

>> INSPECTION END

NG (Less than the SP value)>>GO TO 27.

27.

CHECK “MAS A/F SE-B1”

Select “MAS A/F SE-B1” in “SPEC” of “DATA MONITOR” mode, and check that the indication is within the SP

value.
OK or NG

OK

>> GO TO 28.

NG (Less than the SP value)>>Replace mass air flow sensor, and then GO TO 30. Refer to 

EM-24,

"Exploded View"

.

28.

CHECK INTAKE SYSTEM

Check for the cause of air leak after the mass air flow sensor. Refer to the following.

EC-148

< DTC/CIRCUIT DIAGNOSIS >

[VQ40DE]

TROUBLE DIAGNOSIS - SPECIFICATION VALUE

• Disconnection, looseness, and cracks in air duct

• Looseness of oil filler cap

• Disconnection of oil level gauge

• Open stuck, breakage, hose disconnection, or cracks of PCV valve

• Disconnection or cracks in EVAP purge hose, stuck open of EVAP canister purge volume control solenoid

valve

• Malfunctioning seal un rocker cover gasket

• Disconnection, looseness, or cracks in hoses, such as a vacuum hose, connecting to intake air system parts

• Malfunctioning seal in intake air system, etc.

>> GO TO 30.

29.

CHECK “A/F ALPHA-B1”, “A/F ALPHA-B2”, AND “B/FUEL SCHDL”

Select “A/F ALPHA-B1”, “A/F ALPHA-B2”, and “B/FUEL SCHDL” in “SPEC” of “DATA MONITOR” mode, and

check that each indication is within the SP value. 
OK or NG

OK

>> INSPECTION END

NG

>> Detect malfunctioning part according to 

EC-489, "Symptom Matrix Chart"

.

30.

CHECK “B/FUEL SCHDL”

Select “B/FUEL SCHDL” in “SPEC” of “DATA MONITOR” mode, and then check that the indication is within

the SP value.
OK or NG

OK

>> INSPECTION END

NG

>> Detect malfunctioning part according to 

EC-489, "Symptom Matrix Chart"

.

POWER SUPPLY AND GROUND CIRCUIT

EC-149

< DTC/CIRCUIT DIAGNOSIS >

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POWER SUPPLY AND GROUND CIRCUIT

Diagnosis Procedure

INFOID:0000000009483824

1.

INSPECTION START

Start engine.

Is engine running?
Yes or No

Yes

>> GO TO 8.

No

>> GO TO 2.

2.

CHECK ECM POWER SUPPLY CIRCUIT-I

1. Turn ignition switch OFF and then ON.

2. Check voltage between ECM terminal 109 and ground with CONSULT or tester.

OK or NG

OK

>> GO TO 4.

NG

>> GO TO 3.

3.

DETECT MALFUNCTIONING PART

Check the following.

• Fuse block (J/B) connector M4

• Harness connectors M31, E152

• 10A fuse (No.1)

• Harness for open or short between ECM and fuse

>> Repair harness or connectors.

4.

CHECK GROUND CONNECTIONS

1. Turn ignition switch OFF.

2. Loosen and retighten three ground screws on the body. Refer to 

EC-152, "Ground Inspection"

.

OK or NG

OK

>> GO TO 5.

NG

>> Repair or replace ground connections.

5.

CHECK ECM GROUND CIRCUIT FOR OPEN AND SHORT-I

1. Disconnect ECM harness connector.

2. Check harness continuity between ECM terminals 12, 123, 124 and ground.

Refer to Wiring Diagram.

3. Also check harness for short to power.
OK or NG

OK

>> GO TO 7.

NG

>> GO TO 6.

Voltage: Battery voltage

BBIA0539E

Continuity should exist.