Isuzu KB P190. Manual - part 559

6E–66

ENGINE DRIVEABILITY AND EMISSIONS

• Vehicle service information (service manual, etc.)

• ISUZU field support

• Experience

• Identical vehicle or system for comparison

6. Re-examine the complaint

When you do not successfully find/isolate the problem
after executing a diagnostic path, you should re-
examine the complaint.

What you should do

In this case, you will need to backtrack and review
information accumulated from step 1 through 4 of
Strategy Based Diagnostics. You also should repeat any
procedures that require additional attention.
A previous path may be eliminated from consideration
only if you are certain that all steps were executed as
directed. You must then select another diagnostic path
(step 5a, 5b, 5c or 5d). If all possible options have been
explored, you may call or seek ISUZU field support.

What resources you should use

Whenever possible, you should use the following
resources to facilitate the diagnostic process:

• Service manual

• Accumulated information form a previous diagnostic

path

• Service information and publications

• ISUZU field support

7. Repair and Verify Fix

What you should do

After you have located the cause of the problem, you
must execute a repair by following recommended
service manual procedures.
When the repair is completed, you should verify the fix
by performing the system checks under the conditions
listed in the customer complaint.
If applicable, you should carry out preventive measures
to avoid a repeat complaint.

What resources you should use

Whenever possible, you should use the following
resources to facilitate the repair process:

• Electrical repair procedures

• Service manual information and publications

ENGINE DRIVEABILITY AND EMISSIONS

6E–67

GENERAL SERVICE INFORMATION

Aftermarket Electrical and Vacuum 
Equipment

Aftermarket (add-on) electrical and vacuum equipment
is defined as any equipment which connects to the
vehicle's electrical or vacuum systems that is installed
on a vehicle after it leaves the factory. No allowances
have been made in the vehicle design for this type of
equipment.
NOTE: No add-on vacuum equipment should be added
to this vehicle.
NOTE:  Add-on electrical equipment must only be
connected to the vehicle's electrical system at the
battery (power and ground).
Add-on electrical equipment, even when installed to
these guidelines, may still cause the electric system to
malfunction. This may also include equipment not
connected to the vehicle electrical system such as
portable telephones and radios. Therefore, the first step
in diagnosing any electric problem is to eliminate all
aftermarket electrical equipment from the vehicle. After
this is done, if the problem still exists, it may be
diagnosed in the normal manner.

Electrostatic Discharge Damage

Electronic components used in the ECM are often
designed to carry very low voltage. Electronic
components are susceptible to damage caused by
electrostatic discharge. Less than 100 volts of static
electricity can cause damage to some electronic
components. By comparison, it takes as much as 4000
volts for a person to feel even the zap of a static
discharge.
There are several ways for a person to become
statically charged. The most common methods of
charging are by friction and induction.

• An example of charging by friction is a person sliding

across a vehicle seat.

• Charge by induction occurs when a person with well-

insulated shoes stands near a highly charged object
and momentarily touches ground. Charges of the
same polarity are drained off leaving the person
highly charged with the opposite polarity. Static
charges can cause damage, therefore it is important
to use care when handling and testing electronic
components.

Non-OEM Parts

All of the OBD diagnostics have been calibrated to run
with OEM parts.   Accordingly, if commercially sold
sensor or switch is installed, it makes a wrong diagnosis
and turns on the check engine lamp.
Aftermarket electronics, such as cellular phones,
stereos, and anti-theft devices, may radiate EMI into the
control system if they are improperly installed.  This may
cause a false sensor reading and turn on the check
engine lamp.

Poor Vehicle Maintenance

The sensitivity of OBD diagnostics will cause the check
engine lamp to 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 can not be classified as a “non-vehicle
fault”, but with the sensitivity of OBD diagnostics,
vehicle maintenance schedules must be more closely
followed.

Related System Faults

Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or component.

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

NOTE:  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.

6E–68

ENGINE DRIVEABILITY AND EMISSIONS

On-Board Diagnostic (OBD)

On-Board Diagnostic Tests

A diagnostic test is a series of steps, the result of which
is a pass or fail reported to the diagnostic executive.
When a diagnostic test reports a pass result, the
diagnostic executive records the following data:

• The diagnostic test has been completed since the

last ignition cycle.

• The diagnostic test has passed during the current

ignition cycle.

• The fault identified by the diagnostic test is not

currently active.

When a diagnostic test reports a fail result, the
diagnostic executive records the following data:

• The diagnostic test has been completed since the

last ignition cycle.

• The fault identified by the diagnostic test is currently

active.

• The fault has been active during this ignition cycle.
• The operating conditions at the time of the failure.

The Diagnostic Executive

The Diagnostic Executive is a unique segment of
software which is  designed to coordinate and prioritize
the diagnostic procedures as well as define the protocol
for recording and displaying their results.  The main
responsibilities of the Diagnostic Executive are listed as
follows:

• Commanding the check engine lamp on and off
• DTC logging and clearing
• Current status information on each diagnostic

Diagnostic Information

The diagnostic charts and functional checks are
designed to locate a faulty circuit or component through
a process of logical decisions.  The charts are prepared
with the requirement that the vehicle functioned
correctly at the time of assembly and that there are not
multiple faults present.
There is a continuous self-diagnosis on certain control
functions.  This diagnostic capability is complemented
by the diagnostic procedures contained in this manual.
The language of communicating the source of the
malfunction is a system of diagnostic trouble codes.
When a malfunction is detected by the control module, a
diagnostic trouble code is set and the check engine
lamp is illuminated.

Check Engine Lamp

The check engine lamp looks the same as the check
engine lamp you are already familiar with, the “Check
Engine” lamp. 
Basically, the check engine lamp is turned on when the
ECM detects a DTC that will impact the vehicle
emissions.

• When the check engine lamp remains “ON” while the

engine is running, or when a malfunction is

suspected due to a driveability or emissions problem,
a Powertrain  On-Board Diagnostic (OBD) System
Check must be performed.  The procedures for these
checks are given in On-Board Diagnostic (OBD)
System Check. These checks will expose faults
which may not be detected if other diagnostics are
performed first.

Data Link Connector (DLC)

The provision for communication with the contorl
module is the Data Link Connector (DLC).   It is located
behind the lower front instrument panel.   The DLC is
used to connect to a Tech2.  Some common uses of the
Tech2 are listed below:

• Identifying stored Diagnostic Trouble Codes (DTCs).
• Clearing DTCs.

• Reading serial data.

Verifying Vehicle Repair

Verification of vehicle repair will be more
comprehensive for vehicles with OBD system
diagnostic.  Following a repair, the technician should
perform the following steps:

1. Review and record the Fail Records for the DTC

which has been diagnosed.

2. Clear DTC(s).

3. Operate the vehicle within conditions noted in the

Fail Records.

4. Monitor the DTC status information for the specific

DTC which has been diagnosed until the diagnostic
test associated with that DTC runs.

Following these steps is very important in verifying
repairs on OBD systems.  Failure to follow these steps
could result in unnecessary repairs.

ENGINE DRIVEABILITY AND EMISSIONS

6E–69

Reading Diagnostic Trouble Codes Using a 
Tech 2

The procedure for reading diagnostic trouble code(s) is
to used a diagnostic Tech2.  When reading DTC(s),
follow instructions supplied by Tech2 manufacturer. 

Clearing Diagnostic Trouble Codes

To clear Diagnostic Trouble Codes (DTCs), use the
Tech2 “clear DTCs” or “clear information” function.
When clearing DTCs follow instructions supplied by the
Tech2 manufacturer.

Diagnosis With Tech 2

If no codes are set:

• Refer  to  F1: Data Display and identify the electrical

faults that are not indicated by trouble code.

• Refer to “SYMPTOM DIAGNOSIS”.

If codes are set:

1. Record all trouble codes displayed by Tech 2 and

check id the codes are intermittent.

2. Clear the codes.

3. Drive the vehicle for a test to reproduce the faulty

status.

4. Check trouble codes again using the Tech 2.

5. If no codes is displayed by test driving, the fault is

intermittent. In this case, refer to “DIAGNOSIS
AIDS”.

6. If a code is present, refer to DTC Chart for

diagnosis.

7. Check trouble codes again using the Tech 2.

Tech 2 CONNECTION

Tech 2 scan tool is used to electrically diagnose the
automatic transmission system and to check the
system. The Tech 2 enhances the diagnosis efficiency
though all the troubleshooting can be done without the
Tech 2.

1. Configuration of Tech 2

• Tech 2 scan tool kit (No. 7000086), Tech 2 scan

tool (No. 7000057) and DLC cable (No.
3000095).

• SAE 16/19 adapter (No. 3000098) (3), RS232

loop back connector (No. 3000112) (2) and
PCMCIA card (No. 3000117) (1).

2. Tech 2 Connection

• Check the key switch is turn OFF.

• Insert the PCMCIA card (1) into the Tech 2 (5).

• Connect the SAE 16/19 adapter (3) to the DLC

cable (4).

• Connect the DLC cable (4) to the Tech 2 (5).

• Connect the SAE 16/19 adapter (3) to the data

link connector of the vehicle.

• Turn the key switch of the vehicle ON and press

the “PWR” key of the Tech 2.

• Check the display of the Tech 2.

NOTE:  Be sure to check that the power is not supplied
to the Tech 2 when attaching or removing the PCMCIA
card.