Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Service manual — part 204
ENGINE DRIVEABILITY AND EMISSIONS
6E–57
Step 3: Simulate the symptom and isolate the
problem
Simulate the symptom and isolate the system by
reproducing all possible conditions suggested in Step 1
while monitoring suspected circuits/components/
systems to isolate the problem symptom. Begin with the
most logical circuit/component.
Isolate the circuit by dividing the suspect system into
simpler circuits. Next, confine the problem into a smaller
area of the system. Begin at the most logical point (or
point of easiest access) and thoroughly check the
isolated circuit for the fault, using basic circuit tests.
Hints
You can isolate a circuit by:
• Unplugging connectors or removing a fuse to
separate one part of the circuit from another
• If only component fails to operate, begin testing the
component
• If a number of components do not operate, begin test
at areas of commonality (such as power sources,
ground circuits, switches, main connectors or major
components)
• Substitute a known good part from the parts
department or the vehicle system
• Try the suspect part in a known good vehicle
See Symptom Simulation Tests on the next page for
problem simulation procedures. Refer to service manual
sections 6E and 8A for information about intermittent
diagnosis. Follow procedures for basic circuit testing in
service manual section 8A.
What resources you should use
Whenever appropriate, you should use the following
resources to assist in the diagnostic process:
• Service manual
• Bulletins
• Digital multimeter (with a MIN/MAX feature)
• Tech II and Tech II upload function
• Circuit testing tools (including connector kits/
harnesses and jumper wires)
• Experience
• Intermittent problem solving simulation methods
• Customer complaint check sheet
Symptom Simulation Tests
1. Vibration
This method is useful when the customer complaint
analysis indicates that the problem occurs when the
vehicle/system undergoes some form of vibration.
For connectors and wire harness, slightly shake
vertically and horizontally. Inspect the connector joint
and body for damage. Also, tapping lightly along a
suspected circuit may be helpful.
For parts and sensors, apply slight vibration to the part
with a light tap of the finger while monitoring the system
for a malfunction.
2. Heat
This method is important when the complaint suggests
that the problem occurs in a heated environment. Apply
moderate heat to the component with a hair drier or
similar tool while monitoring the system for a
malfunction.
CAUTION: Care must be take to avoid overheating
the component.
3. Water and Moisture
This method may be used when the complaint suggests
that the malfunction occurs on a rainy day or under
conditions of high humidity. In this case, apply water in a
light spray on the vehicle to duplicate the problem.
CAUTION: Care must be take to avoid directly
exposing electrical connections to water.
4. Electrical loads
This method involves turning systems ON (such as the
blower, lights or rear window defogger) to create a load
on the vehicle electrical system at the same time you
are monitoring the suspect circuit/component.
5e. Vehicle Operates as Designed
This condition refers to instances where a system
operating as designed is perceived to be unsatisfactory
or undesirable. In general, this is due to:
• A lack of understanding by the customer
• A conflict between customer expectations and vehicle
design intent
• A system performance that is unacceptable to the
customer
What you should do
You can verify that a system is operating as designed
by:
• Reviewing manual functional/diagnostic
checks
• Examining bulletins and other service information for
supplementary information
• Compare system operation to an identical vehicle
If the condition is due to a customer misunderstanding
or a conflict between customer expectation and system
operation, you should explain the system operation to
the customer.
If the complaint is due to a case of unsatisfactory
system performance, you should contact Technical
Assistance for the latest information.
What resources you should use
Whenever possible, you should use the following
resources to facilitate the diagnostic process:
6E–58
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
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–59
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–60
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.
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