Isuzu N-Series. Manual - part 745

Engine Control System (4JH1) 6E-31

Brake Pedal 1 Switch
This parameter displays the state of the brake pedal as
determined by the ECM terminal (pin 30) based on an
input from the brake pedal 1 switch. This switch turns
On the stop lamps when the brake pedal is depressed.
The Tech 2 will display Applied when the brake pedal is
depressed.

Brake Pedal 2 Switch
This parameter displays the state of the brake pedal 2
switch as determined by the ECM terminal (pin 65).
The Tech 2 will display Released or Applied. Released
indicates the brake pedal is not being pushed down.
Applied indicates the brake switch is being depressed.

Clutch Pedal Switch
This parameter displays the state of the clutch pedal as
determined by the ECM terminal (pin 31) based on an
input from the clutch pedal switch. The Tech 2 will
display Release or Applied. Release indicates the
clutch pedal is not being push down. Applied indicates
the clutch switch is being depressed.

Engine Warm Up Switch
This parameter displays the input status of the engine
warm up switch to the ECM terminal (pin 46). The Tech
2 will display On or Off. On indicates the engine warm
up switch is closing the engine quick warm up system
request circuit to the ECM. Off indicates the engine
warm up switch is open.

Exhaust Brake Switch
This parameter displays the input status of the exhaust
brake switch to the ECM terminal (pin 64). The Tech 2
will display On or Off. On indicates the exhaust brake
switch is closing the exhaust brake request circuit to
the ECM and allowing to energize the intake throttle
solenoid and exhaust brake solenoid depending on
driving condition. Off indicates the exhaust brake
switch is open and exhaust brake will not engage.

Intake Throttle Solenoid Command
This parameter displays the commanded state of the
intake throttle solenoid valve control circuit (pin 95).
The Tech 2 will display On or Off. On indicates the
intake throttle solenoid valve circuit is being energized
by the ECM. Off indicates the intake throttle solenoid
valve is not being commanded On by the ECM.

Exhaust Brake Solenoid Command
This parameter displays the commanded state of the
exhaust brake solenoid valve control circuit (pin 40).
The Tech 2 will display On or Off. On indicates the
exhaust brake solenoid valve circuit is being energized
by the ECM. Off indicates the exhaust brake solenoid
valve is not being commanded On by the ECM.

ABS Input Signal
This parameter displays the input status of the exhaust
brake cut request from the EHCU (ABS unit) to the
ECM terminal (pin 32). The Tech 2 will display On or
Off. On indicates the EHCU is commanding to the
ECM to release the exhaust brake. Off indicates the
EHCU is not being commanded.

ABS Output Signal
This parameter displays a feedback (output) signal of
exhaust brake cut request from the ECM terminal (pin
62) to the EHCU (ABS unit). On indicates the ECM is
commanding to the EHCU to return a feedback signal.
Off indicates the ECM is not being commanded.

Vehicle Speed
This parameter displays the vehicle speed calculated
by the ECM based on an input from the vehicle speed
sensor (VSS). The Tech 2 will display a high value at
higher vehicle speeds, and low value at lower vehicle
speeds.

Glow Relay Command
This parameter displays the commanded state of the
glow plug relay control circuit (pin 94). The Tech 2 will
display On or Off. On indicates the glow plug relay
control circuit is being grounded by the ECM, allowing
voltage to the glow plugs. Off indicates the glow plug
relay is not being commanded On by the ECM.

Glow Indicator Lamp Command
This parameter displays the commanded state of the
glow indicator lamp control circuit (pin 43). The glow
indicator lamp should be On when the Tech 2 indicates
On. The glow indicator should be Off when the Tech 2
indicates Off.

Malfunction Indicator Lamp (MIL) Command
This parameter displays the commanded state of the
malfunction indicator lamp (MIL) control circuit (pin 42).
The MIL should be On when the Tech 2 indicates On.
The MIL should be Off when the Tech 2 indicates Off.
The ECM will command the MIL On for a certain length
of time when the ignition is On with the engine Off in
order to perform a bulb check.

A/C Request Signal
This parameter displays the state of the air
conditioning (A/C) request input to the ECM terminal
(pin 33) from the heating, ventilation, and air
conditioning (HVAC) controls. The Tech 2 will display
On or Off. On indicates the ECM is receiving a request
from the HVAC system to ground the A/C compressor
relay control circuit, engaging the A/C compressor
clutch. Off indicates the ECM is not receiving a request
from the HVAC system.

A/C Relay Command
This parameter displays the commanded state of the A/
C compressor relay control circuit (pin 41). The Tech 2
will display On or Off. On indicates the A/C compressor
relay control circuit is being grounded by the ECM,
allowing voltage to the A/C compressor clutch. Off
indicates the A/C compressor relay is not being
commanded On by the ECM.

6E-32 Engine Control System (4JH1)

Tech 2 Output Controls

Breaker Box

Breaker Box Connection Type A

Legend

1. Engine Control Module (ECM)
2. Harness Adapter
3. ECM – Harness Connector
4. Breaker Box
5. ECM disconnected

Although probe to the engine control module (ECM)
harness connector is possible by Test Adapter, Breaker
Box Connection Type A is suitable usage to prevent
misprobe and damage of female terminals when test
open circuit or short to ground between the ECM and
electrical components, since the terminals where the
harness connector of the ECM is thin have gathered.

Breaker Box Connection Type B

Legend

1. Engine Control Module (ECM)
2. Harness Adapter
3. ECM – Harness Connector
4. Breaker Box
5. ECM connected

The ECM and other connectors have water proof
terminal that is not allowed to back probe. Breaker Box
Connection Type B is suitable usage to test short to
voltage circuit or signal check between the ECM and
electrical components.

Tech 2 Output Control

Additional Menu

Selection(s)

Descriptions

EGR Solenoid Valve

Solenoids

The purpose of this test is for checking whether the EGR valve is correctly
moved with command. Restricted valve movement by foreign materials,
excessive deposits, a faulty vacuum hose routing, a faulty EGR valve or a
faulty EGR solenoid could be considered if the mass air flow (MAF) sensor is
not changed when commanded ON or OFF.

Engine Speed (RPM)

Control

—

The purpose of this test is for checking whether the actual engine idle speed
can change to match the commanded RPM.

Glow Indicator

Lamps

The purpose of this test is for checking whether the glow indicator lamp is
operating when commanded ON. Faulty circuit(s) or an open bulb could be
considered if not operating when commanded ON.

Glow Relay

Relays

The purpose of this test is for checking whether the glow relay is operating
when commanded ON. Faulty circuit(s) or a faulty glow relay could be
considered if not energizing when commanded ON.

Malfunction Indicator

Lamp

Lamps

The purpose of this test is for checking whether the malfunction indicator
lamp (MIL) is operating when commanded ON. Faulty circuit(s) or an open
bulb could be considered if not operating when commanded ON.

N6A3817E

N6A3818E

Engine Control System (4JH1) 6E-33

Engine Control System Check Sheet

ENGINE CONTROL SYSTEM CHECK SHEET

Inspectors Name

Customer’s Name

Model & Model Year

Driver’s Name

Chassis No.

Date Vehicle Brought In

Engine No.

License No.

Odometer Reading

Km/miles

Engine Does
Not Run

Engine does not crank

No initial combustion

No complete combustion

Hard Start

Engine cranks slowly

Other (

)

Abnormal idling speed

High idling speed ( RPM)

Low idling speed ( RPM)

Rough idling

Incorrect Idle

Other (

)

Hesitation, sag, stumble

Surge, chuggles

Cut out, misses

Lack of power, sluggishness, sponginess

Poor
Driveability

Other (

)

Soon after starting

After accelerator pedal depressed

Engine Stall

During A/C operation

After accelerator pedal released

Shifting from N to D

Other (

)

Black smoke

White smoke

Poor fuel economy

Fuel knock, combustion noise

robl

Others

Other (

)

Dates problem occurred

Constant

Intermittently ( times per day/month)

Once only

Problem frequency

Other (

)

Fine

Cloudy

Rainy

Snow

Weather

Various/Other (

)

Hot (approx. )

Warm

Cool

Cold (approx. )

Outside
Temperature

Any temperature
Highway

Suburbs

City area

Uphill

Place

Downhill

Rough road

Other (

)

Over (approx.

tons)

No load

Load Condition

Other (approx.

tons)

Cold

Warming up

After warming up

Any temperature

Engine
Temperature

Other (

)

Starting

Just after starting (

Min.)

Idling

Racing

Driving

Constant speed

Acceleration

Deceleration

A/C switch On/Off

Engine Operation

Other (

)

Fuel Amount

Full

Above 1/2

Below 1/2

Near empty

Condi

on When

robl

Fuel Bland

Condition of MIL

Remains On

Intermittently turns On

Does not turn On

Present Code

Nothing

P Code & Symptom Code
No. (

)

Diagnostic Trouble
Code (DTC) or Flash
Code

History Code

Nothing

P Code & Symptom Code
No. (

)

Other Additional
Condition

N6A3819E

6E-34 Engine Control System (4JH1)

Diagnostic Starting Point – Engine
Controls

Begin the system diagnosis with Diagnostic System
Check – Engine Controls. The Diagnostic System
Check – Engine Controls will provide the following
information:

• The identification of the control modules which

command the system.

• The ability of the control modules to communicate

through the serial data circuit.

• The identification of any stored diagnostic trouble

codes (DTCs) and their statuses.

The use of the Diagnostic System Check – Engine
Controls will identify the correct procedure for
diagnosing the system and where the procedure is
located.

Important:
Engine Control System Check Sheet must be used to
verify the customer complaint, you need to know the
correct (normal) operating behavior of the system and
verify that the customer complaint is a valid failure of
the system.

Diagnostic System Check – Engine
Controls

Description
The Diagnostic System Check – Engine Controls is an
organized approach to identifying a condition that is
created by a malfunction in the electronic engine
control system. The Diagnostic System Check must be
the starting point for any driveability concern. The
Diagnostic System Check directs the service technician
to the next logical step in order to diagnose the
concern. Understanding and correctly using the
diagnostic table reduces diagnostic time, and prevents
the replacement of good parts.

Test Description
The numbers below refer to the step numbers on the
diagnostic table.
2. Lack of communication may be because of a partial
or a total malfunction of the Keyword 2000 serial data
circuit. The specified procedure determines the
particular condition.

11. If there are other modules with DTCs set, refer to
the DTC list. The DTC list directs you to the
appropriate diagnostic procedure. If the control module
stores multiple DTCs, diagnose the DTCs in the
following order.

• Component level DTCs, such as sensor DTCs,

solenoid DTCs, actuator DTCs, and relay DTCs.
Diagnose the multiple DTCs within this category in
numerical order. Begin with the lowest numbered
DTC, unless the diagnostic table directs you
otherwise.

Diagnostic System Check – Engine Controls
Important:

• DO NOT perform this diagnostic if there is not a

driveability concern, unless another procedure
directs you to this diagnostic.

• Before you proceed with diagnosis, search for

applicable service bulletins.

• Unless a diagnostic procedure instructs you, DO

NOT clear the DTCs.

• If there is a condition with the starting system, refer

to the starting system section in the engine
mechanical.

• Ensure the battery has a full charge.
• Ensure the battery cables (+) (-) are clean and

tight.

• Ensure the ECM grounds are clean, tight, and in

the correct location.

• Ensure the ECM harness connectors are clean

and correctly connected.

• Ensure the ECM terminals are clean and correctly

mating.

• Ensure the fuel injection pump control unit (PCU)

ground is clean, tight, and in the correct location.

• Ensure the PCU harness connectors are clean and

correctly connected.

• Ensure the PCU terminals are clean and correctly

mating.

• Ensure the vehicle maintenance has been done

enough.

Step

Action

Value(s)

Yes

Install the Tech 2.

Does the Tech 2 turn ON?

—

Go to Step 2

Go to Tech 2 Does

Not Power Up

Turn ON the ignition, with the engine OFF.

Attempt to establish communication with the
engine control module (ECM).

Does the Tech 2 communicate with the ECM?

—

Go to Step 3

Go to Lost

Communication with

The Engine Control

Module (ECM)

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