check engine ISUZU TF SERIES 2004 Workshop Manual
[x] Cancel search | Manufacturer: ISUZU, Model Year: 2004, Model line: TF SERIES, Model: ISUZU TF SERIES 2004Pages: 4264, PDF Size: 72.63 MB
Page 2053 of 4264
3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-57
Starting Mode
When the ignition is first turned "ON," the ECM
energizes the fuel pump relay for two seconds to allo
w
the fuel pump to build up pressure. The ECM then
checks the engine coolant temperature (ECT) senso
r
and the throttle position sensor to determine the proper
air/fuel ratio for starting.
The ECM controls the amount of fuel delivered in the
starting mode by adjusting how long the fuel injectors
are energized by pulsing the injectors for very short
times.
Fuel Metering System Components
The fuel metering system is made up of the following
parts.
Fuel injector
Throttle Body
Fuel Rail
Fuel Pressure regulator
ECM
Crankshaft position (CKP) sensor
Camshaft position (CMP) sensor
Idle air control valve
Fuel pump
Fuel Injector
The sequential multi-port fuel injection fuel injector is a
solenoid operated device controlled by the ECM. The
ECM energizes the solenoid, which opens a valve to
allow fuel delivery.
The fuel is injected under pressure in a conical spray
pattern at the opening of the intake valve. Excess fuel
not used by the injectors passes through the fuel
pressure regulator before being returned to the fuel
tank.
Fuel Pressure Regulator
The fuel pressure regulator is a diaphragm-operated
relief valve mounted on the fuel rail with fuel pump
pressure on one side and manifold pressure on the
other side. The fuel pressure regulator maintains the
fuel pressure available to the injector at three times
barometric pressure adjusted for engine load. It may be
serviced separate.
If the pressure is too low, poor performance and a DTC
P0131, P0151, P0171, P0174, P1171 or P1174 will be
the result. If the pressure is too high, excessive odo
r
and/or a DTC P0132, P0152, P0172 or P0175 will be
the result. Refer to Fuel System Diagnosisfo
r
information on diagnosing fuel pressure conditions.
Fuel Rail
The fuel rail is mounted to the top of the engine and
distributes fuel to the individual injectors. Fuel is
delivered to the fuel inlet tube of the fuel rail by the fuel
lines. The fuel goes through the fuel rail to the fuel
pressure regulator. The fuel pressure regulato
r
maintains a constant fuel pressure at the injectors.
Remaining fuel is then returned to the fuel tank.
055RV009
Fuel Pump Electrical Circuit
When the key is first turned "ON," the ECM energizes
the fuel pump relay for two seconds to build up the fuel
pressure quickly. If the engine is not started within two
seconds, the ECM shuts the fuel pump off and waits
until the engine is cranked. When the engine is cranked
and the 58 X crankshaft position signal has been
detected by the ECM, the ECM supplies 12 volts to the
fuel pump relay to energize the electric in-tank fuel
pump.
An inoperative fuel pump will cause a "no-start"
condition. A fuel pump which does not provide enough
pressure will result in poor performance.
Camshaft Position (CMP) Sensor Signal
The ECM uses this signal to determine the position o
f
the number 1 piston during its power stroke, allowing
the ECM to calculate true sequential multiport fuel
injection. Loss of this signal will set a DTC P0341. If the
CMP signal is lost while the engine is running, the fuel
injection system will shift to a calculated sequential fuel
injection based on the last fuel injection pulse, and the
engine will continue to run. The engine can be restarted
and will run in the calculated sequential mode as long
as the fault is present, with a 1-in-6 chance of being
correct.
Page 2055 of 4264
3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-59
Carbon fouling of the spark plug is indicated by dry,
black carbon (soot) deposits on the portion of the spark
plug in the cylinder. Excessive idling and slow speeds
under light engine loads can keep the spark plug
temperatures so low that these deposits are not burned
off. Very rich fuel mixtures or poor ignition system
output may also be the cause. Refer to DTC P0172.
Oil fouling of the spark plug is indicated by wet oily
deposits on the portion of the spark plug in the cylinder,
usually with little electrode wear. This may be caused by
oil during break-in of new or newly overhauled engines.
Deposit fouling of the spark plug occurs when the
normal red-brown, yellow or white deposits o
f
combustion by products become sufficient to cause
misfiring. In some cases, these deposits may melt and
form a shiny glaze on the insulator around the cente
r
electrode. If the fouling is found in only one or two
cylinders, valve stem clearances or intake valve seals
may be allowing excess lubricating oil to enter the
cylinder, particularly if the deposits are heavier on the
side of the spark plug facing the intake valve.
TS23995
Excessive gap means that the air space between the
center and the side electrodes at the bottom of the
spark plug is too wide for consistent firing. This may be
due to excessive wear of the electrode during use.
A
check of the gap size and comparison to the gap
specified for the vehicle in Maintenance and Lubrication
will tell if the gap is too wide. A spark plug gap that is
too small may cause an unstable idle condition.
Excessive gap wear can be an indication of continuous
operation at high speeds or with engine loads, causing
the spark to run too hot. Another possible cause is an
excessively lean fuel mixture.
TS23992
Low or high spark plug installation torque or improper
seating can result in the spark plug running too hot and
can cause excessive center electrode wear. The plug
and the cylinder head seats must be in good contact fo
r
proper heat transfer and spark plug cooling. Dirty or
damaged threads in the head or on the spark plug can
keep it from seating even though the proper torque is
applied. Once spark plugs are properly seated, tighten
them to the torque shown in the Specifications Table.
Low torque may result in poor contact of the seats due
to a loose spark plug. Over tightening may cause the
spark plug shell to be stretched and will result in poo
r
contact between the seats. In extreme cases, exhaus
t
blow-by and damage beyond simple gap wear may
occur.
Cracked or broken insulators may be the result o
f
improper installation, damage during spark plug heat
shock to the insulator material. Upper insulators can be
broken when a poorly fitting tool is used during
installation or removal, when the spark plug is hit from
the outside, or is dropped on a hard surface. Cracks in
the upper insulator may be inside the shell and no
t
visible. Also, the breakage may not cause problems
until oil or moisture penetrates the crack later.
Page 2060 of 4264
6E-64 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Diagnostic Thought Process
As you follow a diagnostic plan, every box on the
Strategy Based Diagnostics chart requires you to use
the diagnostic thought process. This method of thinking
optimizes your diagnosis in the following ways:
Improves your understanding and definition of the
customer complaint
Saves time by avoiding testing and/or replacing
good parts
Allows you to look at the problem from different
perspectives
Guides you to determine what level o
f
understanding about system operation is needed:
Owner’s manual level
Service manual level
In-depth (engineering) level
1. Verify the Complaint
What you should do
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 o
f
the system.
The following information will help you verify the
complaint:
WHAT the vehicle model/options are
WHAT aftermarket and dealer-installed
accessories exist
WHAT related system(s) operate properly
WHEN the problem occurs
WHERE the problem occurs
HOW the problem occurs
HOW LONG the condition has existed (and if the
system ever worked correctly)
HOW OFTEN the problem occurs
Whether the severity of the problem has
increased, decreased or stayed the same
What resources you should use
Whenever possible, you should use the following
resources to assist you in verifying the complaint:
Service manual Theory or Circuit Description
sections
Service manual “System Performance Check”
Owner manual operational description
Technician experience
Identical vehicle for comparison
Circuit testing tools
Vehicle road tests
Complaint check sheet
Contact with the customer
2. Perform Preliminary Checks
NOTE: An estimated 10 percent of successful
vehicle repairs are diagnosed with this step!
What you should do
You perform preliminary checks for several reasons:
To detect if the cause of the complaint is
VISUALLY OBVIOUS
To identify parts of the system that work correctly
To accumulate enough data to correctly and
accurately search for a ISUZU Service Bulletin.
The initial checks may vary depending on the
complexity of the system and may include the following
actions:
Operate the suspect system
Make a visual inspection of harness routing and
accessible/visible power and ground circuits
Check for blown fuses
Make a visual inspection for separated connectors
Make a visual inspection of connectors (includes
checking terminals for damage and tightness)
Check for any DTCs stored by the on-board
computers
Sense unusual noises, smells, vibrations o
r
movements
Investigate the vehicle service history (call othe
r
dealerships, if appropriate)
What resources you should use
Whenever appropriate, you should use the following
resources for assistance in performing preliminary
checks:
Tech 2 or other technical equipment for viewing
DTCs
Service manual information:
Component locations
Harness routing
Wiring schematics
Procedures for viewing DTCs
Dealership service history file
Vehicle road test
Identical vehicle or system for comparison
Page 2061 of 4264
3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-65
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 related
to 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 experience 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 o
r
normally closed?
Is the power switched or is the ground
switched?
Is it a variable resistance circuit (ECT senso
r
or TPS, for example)?
Is it a signal generating device (MAF senso
r
of VSS, for example)?
Page 2063 of 4264
3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-67
What you should do
Step 1: Acquire information
A thorough and comprehensive customer check sheet
is critical to intermittent problem diagnosis. You should
require this, since it will dictate the diagnostic starting
point. The vehicle service history file is another
source for accumulating information about the
complaint.
Step 2: Analyze the intermittent problem
Analyze the customer check sheet and service history
file to determine conditions relevant to the suspect
system(s).
Using service manual information, you must identify,
trace and locate all electrical circuits related to the
malfunctioning system(s). If there is more than one
system failure, you should identify, trace and locate
areas of commonality shared by the suspect circuits.
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 smalle
r
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 powe
r
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 fo
r
problem simulation procedures. Refer to service
manual sections 6E and 8A for information abou
t
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 2 and Tech 2 upload function
Circuit testing tools (including connecto
r
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 complain
t
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 join
t
and body for damage. Also, tapping lightly along a
suspected circuit may be helpful.
For parts and sensors, apply slight vibration to the par
t
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 o
r
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 unde
r
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.
Page 2064 of 4264
6E-68 3.5L ENGINE DRIVEABILITY AND EMISSIONS
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 service 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:
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 o
f
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
Page 2066 of 4264
6E-70 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Fuel Quality
Fuel quality is not a new issue for the automotive
industry, but its potential for turning on the MIL (“Check
Engine" lamp) with OBD systems is new.
Fuel additives such as “dry gas" and “octane
enhancers" may affect the performance of the fuel. The
Reed Vapor Pressure of the fuel can also create
problems in the fuel system, especially during the spring
and fall months when severe ambient temperature
swings occur. A high Reed Vapor Pressure could sho
w
up as a Fuel Trim DTC due to excessive canister
loading. High vapor pressures generated in the fuel
tank can also affect the Evaporative Emission
diagnostic as well.
Using fuel with the wrong octane rating for your vehicle
may cause driveability problems. Many of the majo
r
fuel companies advertise that using “premium" gasoline
will improve the performance of your vehicle. Mos
t
premium fuels use alcohol to increase the octane rating
of the fuel. Although alcohol-enhanced fuels may raise
the octane rating, the fuel's ability to turn into vapor in
cold temperatures deteriorates. This may affect the
starting ability and cold driveability of the engine.
Low fuel levels can lead to fuel starvation, lean engine
operation, and eventually engine misfire.
Non-OEM Parts
All of the OBD diagnostics have been calibrated to run
with OEM parts.
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 MIL
(“Check Engine" lamp).
Environment
Temporary environmental conditions, such as localized
flooding, will have an effect on the vehicle ignition
system. If the ignition system is rain-soaked, it can
temporarily cause engine misfire and turn on the MIL
(“Check Engine" lamp).
Vehicle Marshaling
The transportation of new vehicles from the assembly
plant to the dealership can involve as many as 60 key
cycles within 5Km miles of driving. This type o
f
operation contributes to the fuel fouling of the spark
plugs and will turn on the MIL (“Check Engine" lamp).
Poor Vehicle Maintenance
The sensitivity of OBD diagnostics will cause the MIL
(“Check Engine" lamp) to turn on if the vehicle is no
t
maintained properly. Restricted air filters, fuel filters,
and crankcase deposits due to lack of oil changes o
r
improper oil viscosity can trigger actual vehicle faults
that were not previously monitored prior to OBD. Poo
r
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.
Severe Vibration
The Misfire diagnostic measures small changes in the
rotational speed of the crankshaft. Severe driveline
vibrations in the vehicle, such as caused by an
excessive amount of mud on the wheels, can have the
same effect on crankshaft speed as misfire.
Related System Faults
Many of the OBD system diagnostics will not run if the
ECM detects a fault on a related system or component.
One example would be that if the ECM detected a
Misfire fault, the diagnostics on the catalytic converte
r
would be suspended until Misfire fault was repaired. If
the Misfire fault was severe enough, the catalytic
converter could be damaged due to overheating and
would never set a Catalyst DTC until the Misfire faul
t
was repaired and the Catalyst diagnostic was allowed to
run to completion. If this happens, the customer may
have to make two trips to the dealership in order to
repair the vehicle.
Maintenance Schedule
Refer to the Maintenance Schedule.
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 othe
r
components.
Inspect all wires in the engine compartment fo
r
proper connections, burned or chafed spots, pinched
wires, contact with sharp edges or contact with ho
t
exhaust manifolds or pipes.
Page 2067 of 4264
3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-71
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.
Serial Data Communications
Class II Serial Data Communications
This vehicle utilizes the “Class II" communication
system. Each bit of information can have one of two
lengths: long or short. This allows vehicle wiring to be
reduced by transmitting and receiving multiple signals
over a single wire. The messages carried on Class II
data streams are also prioritized. If two messages
attempt to establish communications on the data line at
the same time, only the message with higher priority will
continue. The device with the lower priority message
must wait. The most significant result of this regulation
is that it provides Tech 2 manufacturers with the
capability to access data from any make or model
vehicle that is sold.
The data displayed on the other Tech 2 will appear the
same, with some exceptions. Some scan tools will only
be able to display certain vehicle parameters as values
that are a coded representation of the true or actual
value. For more information on this system of coding,
refer to Decimal/Binary/Hexadecimal Conversions.On
this vehicle the Tech 2 displays the actual values fo
r
vehicle parameters. It will not be necessary to perform
any conversions from coded values to actual values.
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 curren
t
ignition cycle.
The fault identified by the diagnostic test is no
t
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.
Remember, a fuel trim DTC may be triggered by a list o
f
vehicle faults. Make use of all information available
(other DTCs stored, rich or lean condition, etc.) when
diagnosing a fuel trim fault.
Comprehensive Component Monitor
Diagnostic Operation
Input Components:
Input components are monitored for circuit continuity
and out-of-range values. This includes rationality
checking. Rationality checking refers to indicating a
fault when the signal from a sensor does not seem
reasonable, i.e.throttle position sensor that indicates
high throttle position at low engine loads. Inpu
t
components may include, but are not limited to the
following sensors:
Vehicle Speed Sensor (VSS)
Inlet Air Temperature (IAT) Sensor
Crankshaft Position (CKP) Sensor
Throttle Position Sensor (TPS)
Engine Coolant Temperature (ECT) Sensor
Camshaft Position (CMP) Sensor
Mass Air Flow (MAF) Sensor
In addition to the circuit continuity and rationality check
the ECT sensor is monitored for its ability to achieve a
steady state temperature to enable closed loop fuel
control.
Output Components:
Output components are diagnosed for proper response
to control module commands. Components where
functional monitoring is not feasible will be monitored fo
r
circuit continuity and out-of-range values if applicable.
Output components to be monitored include, but are no
t
limited to, the following circuit:
Idle Air Control (IAC) Valve
Control module controlled EVAP Canister Purge
Valve
Electronic Transmission controls
A/C relays
VSS output
MIL control
Refer to ECM and Sensors in General Descriptions.
Page 2068 of 4264
6E-72 3.5L ENGINE DRIVEABILITY AND EMISSIONS
Passive and Active Diagnostic Tests
A passive test is a diagnostic test which simply monitors
a vehicle system or component. Conversely, an active
test, actually takes some sort of action when performing
diagnostic functions, often in response to a failed
passive test.
Intrusive Diagnostic Tests
This is any on-board test run by the Diagnostic
Management System which may have an effect on
vehicle performance or emission levels.
Warm-Up Cycle
A warm-up cycle means that engine at temperature
must reach a minimum of 70
C (160F) andrise at
least 22
C (40F) over the course of a trip.
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 MIL (“Check Engine" lamp) on and
off
DTC logging and clearing
Freeze Frame data for the first emission related DTC
recorded
Current status information on each diagnostic
The Diagnostic Executive records DTCs and turns on
the MIL when emission-related faults occur. It can also
turn off the MIL if the conditions cease which caused
the DTC to set.
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 no
t
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 MIL (“Check
Engine" lamp) is illuminated.
Check Engine Lamp (MIL)
The Check Engine Lamp (MIL) looks the same as the
MIL you are already familiar with (“Check Engine"
lamp).
Basically, the MIL is turned on when the ECM detects a
DTC that will impact the vehicle emissions.
The MIL is under the control of the Diagnostic
Executive. The MIL will be turned on if an
emissions-related diagnostic test indicates a
malfunction has occurred. It will stay on until the
system or component passes the same test, for three
consecutive trips, with no emissionsrelated faults.
Extinguishing the MIL
When the MIL is on, the Diagnostic Executive will turn
off the MIL after three consecutive trips that a “tes
t
passed" has been reported for the diagnostic test tha
t
originally caused the MIL to illuminate.
Although the MIL has been turned off, the DTC will
remain in the ECM memory (both Freeze Frame and
Failure Records) until forty(40) warm-up cycles after no
faults have been completed.
If the MIL was set by either a fuel trim or misfire-related
DTC, additional requirements must be met. In addition
to the requirements stated in the previous paragraph,
these requirements are as follows:
The diagnostic tests that are passed must occur with
375 RPM of the RPM data stored at the time the las
t
test failed.
Plus or minus ten (10) percent of the engine load tha
t
was stored at the time the last failed.
Similar engine temperature conditions (warmed up o
r
warming up ) as those stored at the time the last tes
t
failed.
Meeting these requirements ensures that the fault which
turned on the MIL has been corrected.
The MIL (“Check Engine" lamp) is on the instrumen
t
panel and has the following functions:
It informs the driver that a fault that affects vehicle
emission levels has occurred and that the vehicle
should be taken for service as soon as possible.
As a bulb and system check, the MIL will come “ON"
with the key “ON" and the engine not running. When
the engine is started, the MIL will turn “OFF."
When the MIL 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.
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3.5L ENGINE DRIVEABILITY AND EMISSIONS 6E-73
Intermittent Check Engine Lamp
In the case of an “intermittent" fault, the MIL (“Check
Engine" lamp) may illuminate and then (after three trips)
go “OFF". However, the corresponding diagnostic
trouble code will be stored in the memory. When
unexpected diagnostic trouble codes appear, check fo
r
an intermittent malfunction.
A diagnostic trouble code may reset. Consult the
“Diagnostic Aids" associated with the diagnostic trouble
code. A physical inspection of the applicable sub–
system most often will resolve the problem.
Data Link Connector (DLC)
The provision for communication with the control
module is the Data Link Connector (DLC). The DLC is
used to connect to a Tech 2. Some common uses o
f
the Tech 2 are listed below:
Identifying stored Diagnostic Trouble Codes (DTCs).
Clearing DTCs.
Performing out put control tests.
Reading serial data.
060RW046
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 and/or Freeze
Frame data for the DTC which has been diagnosed
(Freeze Frame data will only be stored for an A or B
type diagnostic and only if the MIL has been
requested).
2. Clear DTC(s).
3. Operate the vehicle within conditions noted in the
Fail Records and/or Freeze Frame data.
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 are very important in verifyin
g
repairs on OBD systems. Failure to follow these steps
could result in unnecessary repairs.
Reading Flash Diagnostic Trouble Codes
The provision for communicating with the Engine
Control Module (ECM) is the Data Link Connecto
r
(DLC). The DLC is located behind the lower front
instrument panel. It is used in the assembly plant to
receive information in checking that the engine is
operating properly before it leaves the plant.
The diagnostic trouble code(s) (DTCs) stored in the
ECM's memory can be read either through a hand-held
diagnostic scanner plugged into the DLC or by counting
the number of flashes of the Check Engine Lamp (MIL)
when the diagnostic test terminal of the DLC is
grounded. The DLC terminal “6" (diagnostic request) is
pulled “Low" (grounded) by jumpering to DLC terminal
“4", which is a ground wire.
This will signal the ECM that you want to “flash" DTC(s),
if any are present. Once terminals “4" and “6" have
been connected, the ignition switch must be moved to
the “ON" position, with the engine not running. At this
point, the “Check Engine" MIL should flash DTC12
three times consecutively.
This would be the following flash, sequence: "flash,
pause, flash?flash, long pause, flash, pause,
flash?flash, long pause, flash, pause, flash?flash". DTC
12 indicates that the ECM's diagnostic system is
operating. If DTC 12 is not indicated, a problem is
present within the diagnostic system itself, and should
be addressed by consulting the appropriate diagnostic
chart in DRIVEABILITY AND EMISSIONS.
Following the output of DTC 12, the “Check Engine" MIL
will indicate a DTC three times if a DTC is present, or i
t
will simply continue to output DTC12. If more than one
DTC three has been stored in the ECM's memory, the
DTC(s) will be output from the lowest to the highest,
with each DTC being displayed three times.
Reading Diagnostic Trouble Codes Using a
TECH 2
The procedure for reading diagnostic trouble code(s) is
to used a diagnostic Tech 2. When reading DTC(s),
follow instructions supplied by Tech 2 manufacturer.
For the 1998 model year, Isuzu dealer service
departments will continue to use Tech 2.