Isuzu D-Max / Isuzu Rodeo (TFR/TFS). Manual - part 822

6E–17

3.2L ENGINE DRIVEABILITY AND EMISSIONS

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3.2L ENGINE DRIVEABILITY AND EMISSIONS

Fuse and Relay Panel (Underhood Electrical Center)

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3.2L ENGINE DRIVEABILITY AND EMISSIONS

Diagnosis

Strategy-Based Diagnostics

Strategy-Based Diagnostics

The strategy-based diagnostic is a uniform approach to
repair all Electrical/Electronic (E/E) systems.  The
diagnostic flow can always be used to resolve an E/E
system problem and is a starting point when repairs are
necessary.  The following steps will instruct the technician
how to proceed with a diagnosis:
1. Verify the customer complaint.

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To verify the customer complaint, the technician
should know the normal operation of the system.

2. Perform preliminary checks.

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Conduct a thorough visual inspection.

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Review the service history.

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Detect unusual sounds or odors.

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Gather diagnostic trouble code information to
achieve an effective repair.

3. Check bulletins and other service information.

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This includes videos, newsletters, etc.

4. Refer to service information (manual) system

check(s).

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“System checks” contain information on a system
that may not be supported by one or more DTCs.
System checks verify proper operation of the
system.  This will lead the technician in an
organized approach to diagnostics.

5. Refer to service diagnostics.

DTC Stored

Follow the designated DTC chart exactly to make an
effective repair.

No DTC

Select the symptom from the symptom tables.  Follow the
diagnostic paths or suggestions to complete the repair.
You may refer to the applicable component/system check
in the system checks.

No Matching Symptom

1. Analyze the complaint.
2. Develop a plan for diagnostics.
3. Utilize the wiring diagrams and the theory of

operation.

Call technical assistance for similar cases where repair
history may be available.  Combine technician knowledge
with efficient use of the available service information.

Intermittents

Conditions that are not always present are called
intermittents.  To resolve intermittents, perform the
following steps:
1. Observe history DTCs, DTC modes, and freezeframe

data.

2. Evaluate the symptoms and the conditions described

by the customer.

3. Use a check sheet or other method to identify the

circuit or electrical system component.

4. Follow the suggestions for intermittent diagnosis

found in the service documentation.

Most scan tools, such as the Tech 2 and the J
39200:DVM, have data-capturing capabilities that can
assist in detecting intermittents.

No Trouble Found

This condition exists when the vehicle is found to operate
normally.  The condition described by the customer may
be normal.  Verify the customer complaint against another
vehicle that is operating normally.  The condition may be
intermittent.  Verify the complaint under the conditions
described by the customer before releasing the vehicle.
1. Re-examine the complaint.

When the complaint cannot be successfully found or
isolated, a re-evaluation is necessary.  The complaint
should be re-verified and could be intermittent as
defined in 

Intermittents, or could be normal.

2. Repair and verify.

After isolating the cause, the repairs should be made.
Validate for proper operation and verify that the
symptom has been corrected.  This may involve road
testing or other methods to verify that the complaint
has been resolved under the following conditions:

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Conditions noted by the customer.

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If a DTC was diagnosed, verify a repair by
duplicating conditions present when the DTC was
set as noted in the Failure Records or Freeze
Frame data.

Verifying Vehicle Repair

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

IMPORTANT:

Follow the steps below when you verify

repairs on OBD systems.  Failure to follow these steps
could result in unnecessary repairs.

1. Review and record the Failure Records and the

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 (“Check
Engine” lamp) has been requested).

2. Clear the DTC(s).
3. Operate the vehicle within conditions noted in the

Failure Records and 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.

6E–20

3.2L ENGINE DRIVEABILITY AND EMISSIONS

General Service Information

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 show 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 major fuel
companies advertise that using “premium” gasoline will
improve the performance of your vehicle.  Most 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 of 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 not
maintained properly.  Restricted air 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.

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 converter 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 fault 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.

Maitenance 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:

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Inspect all vacuum hoses for punches, cuts,
disconnects, and correct routing.

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Inspect hoses that are difficult to see behind other
components.

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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 effec-
tively use this section of the Service Manual.