diagram ISUZU TF SERIES 2004 Workshop Manual

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–17
ECM CIRCUIT DIAGRAM (4JH1-TC)

6E–46 4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
ECM WIRING DIAGRAM (1/7)

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–47
ECM WIRING DIAGRAM (2/7)

6E–48 4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
ECM WIRING DIAGRAM (3/7)

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–49
ECM WIRING DIAGRAM (4/7)

6E–50 4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
ECM WIRING DIAGRAM (5/7)

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–51
ECM WIRING DIAGRAM (6/7)

6E–52 4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
ECM WIRING DIAGRAM (7/7)

6E–78 4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS
3. Check Bulletins and
Troubleshooting Hints
NOTE: As estimated 30 percent of successful vehicle
repairs are diagnosed with this step!
What you should do
You should have enough information gained from
preliminary checks to accurately search for a bulletin
and other related service information. Some service
manual sections provide troubleshooting hints that
match symptoms with specific complaints.
What resources you should use
You should use the following resources for assistance in
checking for bulletins and troubleshooting hints:
Printed bulletins
Access ISUZU Bulletin Web site.
Videotapes
Service manual
4. Perform Service Manual
Diagnostic Checks
What you should do
The “System Checks” in most service manual sections
and in most cells of section 8A (electrical) provide you
with:
A systematic approach to narrowing down the
possible causes of a system fault
Direction to specific diagnostic procedures in the
service manual
Assistance to identify what systems work correctly
What resources you should use
Whenever possible, you should use the following
resources to perform service manual checks:
Service manual
Technical equipment (for viewing DTCs and
analyzing data)
Digital multimeter and circuit testing tools
Other tools as needed
5a and 5b. Perform Service Manual
Diagnostic Procedures
NOTE: An estimated 40 percent of successful vehicle
repairs are diagnosed with these steps!
What you should do
When directed by service manual diagnostic checks,
you must then carefully and accurately perform the
steps of diagnostic procedures to locate the fault relatedto the customer complaint.
What resources you should use
Whenever appropriate, you should use the following
resources to perform service manual diagnostic
procedures:
Service manual
Technical equipment (for analyzing diagnostic data)
Digital multimeter and circuit testing tools
Essential and special tools
5c. Technician Self Diagnoses
When there is no DTC stored and no matching
symptom for the condition identified in the service
manual, you must begin with a thorough understanding
of how the system(s) operates. Efficient use of the
service manual combined with you ex perience and a
good process of elimination will result in accurate
diagnosis of the condition.
What you should do
Step 1: Identify and understand the suspect
circuit(s)
Having completed steps 1 through 4 of the Strategy
Based Diagnostics chart, you should have enough
information to identify the system(s) or sub-system(s)
involved. Using the service manual, you should
determine and investigate the following circuit
characteristics:
Electrical:
–How is the circuit powered (power distribution
charts and/or fuse block details)?
–How is the circuit grounded (ground distribution
charts)?
–How is the circuit controlled or sensed (theory of
operation):
–If it is a switched circuit, is it normally open or
normally closed?
–Is the power switched or is the ground
switched?
–Is it a variable resistance circuit (ECT sensor
or TP sensor, for ex ample)?
–Is it a signal generating device (MAF sensor of
VSS, for example)?
–Does it rely on some mechanical/vacuum
device to operate?
Physical:
–Where are the circuit components (component
locators and wire harness routing diagrams):
–Are there areas where wires could be chafed
or pinched (brackets or frames)?
–Are there areas subjected to ex treme
temperatures?

4JA1/4JH1 ENGINE DRIVEABILITY AND EMISSIONS 6E–361
SYMPTOM DIAGNOSIS
PRELIMINARY CHECKS
Before using this section, perform the “On-Board
Diagnostic (OBD) System Check” and verify all of the
following items:
The engine control module (ECM) and check engine
lamp (MIL=malfunction indicator lamp are operating
correctly.
There are no Diagnostic Trouble Code(s) stored.
Tech 2 data is within normal operating range. Refer to
Typical Scan Data Values.
Verify the customer complaint and locate the correct
symptom in the table of contents. Perform the
procedure included in the symptom chart.
VISUAL/PHYSICAL CHECK
Several of the symptom procedures call for a careful
visual/physical check. This can lead to correcting a
problem without further checks and can save valuable
time. This check should include the following items:
ECM grounds for cleanliness, tightness and proper
location.
Vacuum hoses for splits, kinks, and proper
connection. Check thoroughly for any type of leak or
restriction.
Air intake ducts for collapsed or damaged areas.
Air leaks at throttle body mounting area, mass air flow
(MAF) sensor and intake manifold sealing surfaces.
Wiring for proper connections, pinches and cuts.
INTERMITTENT
Important: An intermittent problem may or may not turn
on the check engine lamp (MIL=malfunction indicator
lamp) or store a Diagnostic Trouble Code. Do NOT use
the Diagnostic Trouble Code (DTC) charts for
intermittent problems.
The fault must be present to locate the problem.
Most intermittent problems are cased by faulty electrical
connections or wiring. Perform a careful visual/physical
check for the following conditions.
Poor mating of the connector halves or a terminal not
fully seated in the connector (backed out).
Improperly formed or damaged terminal.
All connector terminals in the problem circuit should
be carefully checked for proper contact tension.
Poor terminal-to-wire connection. This requires
removing the terminal form the connector body to
check.
Check engine lamp (MIL=malfunction indicator lamp)
wire to ECM shorted to ground.
Poor ECM grounds. Refer to the ECM wiring
diagrams.Road test the vehicle with a Digital Multimeter
connected to a suspected circuit. An abnormal voltage
when the malfunction occurs is a good indication that
there is a fault in the circuit being monitored.
Using Tech 2 to help detect intermittent conditions. The
Tech 2 have several features that can be used to
located an intermittent condition. Use the following
features to find intermittent faults:
To check for loss of diagnostic code memory,
disconnect the MAF sensor and idle the engine until the
check engine lamp (MIL=malfunction indicator lamp)
comes on. Diagnostic Trouble Code P0100 should be
stored and kept in memory when the ignition is turned
OFF.
If not, the ECM is faulty. When this test is completed,
make sure that you clear the Diagnostic Trouble Code
P0100 from memory.
An intermittent check engine lamp (MIL=malfunction
indicator lamp) with no stored Diagnostic Trouble Code
may be caused by the following:
Check engine lamp (MIL=malfunction indicator lamp)
wire to ECM short to ground.
Poor ECM grounds. Refer to the ECM wiring
diagrams.
Check for improper installation of electrical options such
as light, cellular phones, etc. Check all wires from ECM
to the ignition control module for poor connections.
Check for an open diode across the A/C compressor
clutch and check for other open diodes (refer to wiring
diagrams in Electrical Diagnosis).
If problem has not been found, refer to ECM connector
symptom tables.
Check the “Broadcast Code” of the ECM, and
compare it with the latest Isuzu service bulletins and/
or Isuzu EEPROM reprogramming equipment to
determine if an update to the ECM's reprogrammable
memory has been released.
This identifies the contents of the reprogrammable
software and calibration contained in the ECM.
If the “Broadcast Code” is not the most current
available, it is advisable to reprogram the ECM's
EEPROM memory, which may either help identify a
hard-to find problem or may fix the problem.
The Service Programming System (SPS) will not allow
incorrect software programming or incorrect calibration
changes.