Isuzu N-Series. Manual - part 743

 Engine Control System (4JH1)    6E-23

Exhaust Brake Solenoid Valve

Fuel Injection Pump Control Unit (PCU)

3

BLU/RED

Engine Warm Up Switch 12V 
Feed

4

BRN/RED

Indicator Lamp Voltage Feed 
From Switch Signal

5

BLK

Illumination Lamp Ground

6

BRN/RED

Engine Warm Up Switch Signal

Connector No.

J-31

Connector Color

Black

Test Adapter No.

J-35616-33

Pin

Wire Color

Pin Function

1

BLK

Ignition Voltage

2

LT GRN

Exhaust Brake Solenoid Control

Connector No.

B-31

Connector Color

Gray

Test Adapter No.

J-35616-42

Pin

Wire Color

Pin Function

1

2

N6A3807E

Connector No.

E-110

Connector Color

Black

Test Adapter No.

J-35616-8

Pin

Wire Color

Pin Function

1

BLU

CAN Low Signal

2

YEL

CAN High Signal

3

—

Not Used

4

—

Not Used

5

ORN

Engine Shutoff (ESO) Solenoid 
Valve Control Signal Input

6

BLK

Ground

7

RED/WHT

Battery voltage 

8

PNK

CKP Sensor Signal Input

9

—

Not Used

2

3

4

5

6

1

9

8

7

N6A3808E

6E-24    Engine Control System (4JH1) 

Glow Plug

Idle Switch

Intake Throttle Solenoid Valve

Mass Air Flow (MAF) / Intake Air Temperature
Sensor

Connector No.

J-122

Connector Color

Silver

Pin

Wire Color

Pin Function

1

BLK/YEL

Power Supply

Connector No.

B-340

Connector Color

Black

Test Adapter No.

J-35616

Pin

Wire Color

Pin Function

1

GRN/BLK

Idle Switch Signal

2

BLK

Idle Switch Ground

N6A3809E

1 2

N6A3810E

Connector No.

J-40

Connector Color

Brown

Test Adapter No.

J-35616-4A

Pin

Wire Color

Pin Function

1

BLU/RED

Ignition Voltage

2

LT GRN/ 

WHT

Intake Throttle Solenoid Control

Connector No.

J-182

Connector Color

Black

Test Adapter No.

J-35616-4A

Pin

Wire Color

Pin Function

1

BLK/BLU

IAT Sensor Signal

1

2

N6A3811E

1

2

3

4

5

N6A3812E

 Engine Control System (4JH1)    6E-25

Vehicle Speed Sensor (VSS)

2

BLU/RED

MAF Sensor Ignition Voltage 
Feed

3

BLK/RED

MAF Sensor & IAT Sensor Low 
Reference

4

WHT/RED

MAF Sensor 5 Volts Reference

5

GRN/RED

MAF Sensor Signal

Connector No.

J-32

Connector Color

Gray

Test Adapter No.

J-35616-64A

Pin

Wire Color

Pin Function

1

BLK/YEL

VSS 12 Volts Feed

2

BLK

VSS Low Reference

3

YEL/GRN

VSS Signal

Connector No.

J-182

Connector Color

Black

Test Adapter No.

J-35616-4A

Pin

Wire Color

Pin Function

1

2

3

N6A3813E

6E-26    Engine Control System (4JH1) 

Diagnostic Information and Procedures

General Service Information

Non-OEM Parts
All of the on-board diagnostic (OBD) has been
calibrated to run with original equipment manufacturer
(OEM) parts.  Accordingly, if commercially sold sensor
or switch is installed, it makes a wrong diagnosis and
turn on the malfunction indicator lamp (MIL).
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may indicate
electromagnetic interference (EMI) into the control
system if they are improperly installed.  This may cause
a false sensor reading and turn on the MIL.

Poor Vehicle Maintenance
The sensitivity of OBD will cause the MIL turn on if the
vehicle is not maintained properly.  Restricted oil filters,
fuel filters, and crankcase deposits due to lack of oil
changes or improper oil viscosity can trigger actual
vehicle faults that were not previously monitored prior
to OBD.  Poor vehicle maintenance cannot be
classified as a “non-vehicle fault”, but with the
sensitivity of OBD diagnostics, vehicle maintenance
schedules must be more closely followed.

Visual/Physical Engine Compartment Inspection
Perform a careful visual and physical engine
compartment inspection when performing any
diagnostic procedure or diagnosing the cause of an
emission test failure.  This can often lead to repairing a
problem without further steps.  Use the following
guidelines when performing a visual/physical
inspection:

• Inspect all vacuum hoses for punches, cuts,

disconnects, and correct routing.

• Inspect hoses that are difficult to see behind other

components.

• Inspect all wires in the engine compartment for

proper connections, burned or chafed spots,
pinched wires, contact with sharp edges or contact
with hot exhaust manifolds or pipes.

Basic Knowledge of Tools Required
Lack of basic knowledge of this powertrain when
performing diagnostic procedures could result in an
incorrect diagnosis or damage to powertrain
components.  Do not attempt to diagnose a powertrain
problem without this basic knowledge.  A basic
understanding of hand tools is necessary to effectively
use this section of the service manual.

Malfunction Indicator Lamp (MIL)
Basically, the MIL is turned on when the ECM detects a
DTC that will impact the vehicle emissions.  When the
MIL remains “ON” while the engine is running, or when
a malfunction is suspected due to a driveability or
emissions problem, a Diagnostic System Check must
be performed.  The procedures for these checks are
given in Diagnostic System Check – Engine Controls.

DTC Types
Characteristic of Code

• Non-Emissions related
• Dose not request illumination of any lamp
• Stores a DTC on the first trip with a fail

Reading Flash Diagnostic Trouble Codes
The provision for communicating with the ECM is the
Data Link Connector (DLC).  The DTCs stored in the
ECM memory can be read either through a hand-held
diagnostic scanner such as Tech 2 plugged into the
DLC or by counting the number of flashes of the MIL
when the diagnostic test terminal of the DLC is
grounded.  The DLC terminal “6” (diagnostic request
switch) is pulled “Low” (grounded) by jumped to DLC
terminal “4”, which is a ground wire.
Once terminals “4” and “6” have been connected, the
ignition switch must be moved to the “ON” position, with
the engine not running.  The MIL will initially flash 12.
Then, the MIL will flash the first stored DTC three
times, second stored DTC three times and so on.  All
the stored DTCs are flashed, then return 12 and
continue to flash the DTC.  If no DTC exists, the MIL
flashes 12 continuously.  The flash DTC display will
continue as long as the DLC is shorted.