2007 ISUZU KB P190 Engine

ENGINE DRIVEABILITY AND EMISSIONS 6E–59
POSITIVE CRANKCASE VENTILATION
(PCV) SYSTEM
Crankcase Ventilation System Purpose
The crankcase ventilation system is used to consume
crankcase vapors in the combustion process instead of
venting them to the atmosphere. Fresh air from the
throttle body is supplied to the crankcase and mixed
with blow-by gases. This mixture is then passed through
the positive crankcase ventilation (PCV) port into the
intake manifold.
While the engine is running, exhaust gases and small
amounts of the fuel/air mixture escape past the piston
rings and enter the crankcase. these gases are mixed
with clean air entering through a tube from the air intake
duct.
During normal, part-throttle operation, the system is
designed to allow crankcase gases to flow through the
PCV hose into the intake manifold to be consumed by
normal combustion.
A plugged positive crankcase ventilation port or PCV
hose may cause the following conditions:
• Rough idle.
• Stalling or slow idle speed.
• Oil leaks.
• Sludge in the engine.
A leaking PCV hose would cause:
• Rough idle.
• Stalling.
• High idle speed.

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6E–60 ENGINE DRIVEABILITY AND EMISSIONS
A/C CLUTCH DIAGNOSIS
A/C Clutch Circuit Operation
A 12-volt signal is supplied to the A/C request input of
the ECM when the A/C is selected through the A/C
control switch.
The A/C compressor clutch relay is controlled through
the ECM. This allows the ECM to modify the idle air
control position prior to the A/C clutch engagement for
better idle quality. If the engine operating conditions are
within their specified calibrated acceptable ranges, the
ECM will enable the A/C compressor relay. This is done
by providing a ground path for the A/C relay coil within
the ECM. When the A/C compressor relay is enabled,
battery voltage is supplied to the compressor relay is
enabled, battery voltage is supplied to the compressor
clutch coil.
The ECM will enable the A/C compressor clutch
whenever the engine is running and the A/C has been
requested. The ECM will not enable the A/C
compressor clutch if any of the following conditions are
met:
• The engine speed is greater than 6000 RPM.
• The ECT is greater than 122°C (251°F).
• The throttle is more than 95% open.
A/C Clutch Circuit Purpose
The A/C compressor operation is controlled by the
engine control module (ECM) for the following reasons:
• It improves idle quality during compressor clutch engagement.
• It improves wide open throttle (WOT) performance.
• It provides A/C compressor protection from operation with incorrect refrigerant pressures.
The A/C electrical system consists of the following
components:
• The A/C control switch.
• The A/C refrigerant pressure switches.
• The A/C compressor clutch.
• The A/C compressor clutch relay.
•The ECM.
A/C Request Signal
This signal tells the ECM when the A/C mode is
selected at the A/C control switch. The ECM uses this
input to adjust the idle speed before turning on the A/C
clutch. The A/C compressor will be inoperative if this
signal is not available to the ECM.
Refer to A/C Clutch Circuit Diagnosis for A/C wiring
diagrams and diagnosis for the A/C electrical system.

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ENGINE DRIVEABILITY AND EMISSIONS 6E–61
ISUZU STRATEGY BASED DIAGNOSTICS
Overview
As a retail service technician, you are part of the ISUZU
service team. The team goal is FIX IT RIGHT THE
FIRST TIME for the satisfaction of every customer. You
are a very important member of the team as you
diagnose and repair customer vehicles. You have maximum efficiency in diagnosis when you
have an effective, organized plan for your work.
Strategy Based Diagnostics (refer to Figure 1) provides
you with guidance as you create and follow a plan of
action for each specific diagnostic situation.
STRATEGY BASED DIAGNOSTICS CHART

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6E–62 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 of understanding about system operation is needed:
– Owner’s manual level
– Service manual level
– In-depth (engineering) level – 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 of 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 on
ISUZU Web site.
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 or movements
• Investigate the vehicle service history (call other dealerships, if appropriate)
What resources you should use
Whenever appropriate, you should use the following
resources for assistance in performing preliminary
checks:
• Tech II 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

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ENGINE DRIVEABILITY AND EMISSIONS 6E–63
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 distributioncharts 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 example)?
– 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 (componentlocators and wire harness routing diagrams):
– Are there areas where wires could be chafed or pinched (brackets or frames)?
– Are there areas subjected to extreme temperatures?

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6E–64 ENGINE DRIVEABILITY AND EMISSIONS
– Are there areas subjected to vibration ormovement (engine, transmission or
suspension)?
– Are there areas exposed to moisture, road salt or other corrosives (battery acid, oil or other
fluids)?
– Are there common mounting areas with other systems/components?
– Have previous repairs been performed to wiring, connectors, components or mounting areas
(causing pinched wires between panels and
drivetrain or suspension components without
causing and immediate problem)?
– Does the vehicle have aftermarket or dealer- installed equipment (radios, telephone, etc.)
Step 2: Isolate the problem
At this point, you should have a good idea of what could
cause the present condition, as well as could not cause
the condition. Actions to take include the following:
• Divide (and separate, where possible) the system or circuit into smaller sections
• Confine the problem to a smaller area of the vehicle (start with main harness connections while removing
panels and trim as necessary in order to eliminate
large vehicle sections from further investigation)
• For two or more circuits that do not share a common power or ground, concentrate on areas where
harnesses are routed together or connectors are
shared (refer to the following hints)
Hints
Though the symptoms may vary, basic electrical failures
are generally caused by:
• Loose connections: – Open/high resistance in terminals, splices,connectors or grounds
• Incorrect connector/harness routing (usually in new vehicles or after a repair has been made):
– Open/high resistance in terminals, splices, connectors of grounds
• Corrosion and wire damage:
– Open/high resistance in terminals, splices,connectors of grounds
• Component failure: – Opens/short and high resistance in relays,modules, switches or loads
• Aftermarket equipment affecting normal operation of other systems
You may isolate circuits by:
• Unplugging connectors or removing a fuse to separate one part of the circuit from another part
• Operating shared circuits and eliminating those that function normally from the suspect circuit
• If only one component fails to operate, begin testing at the component
• If a number of components do no operate, begin tests at the area of commonality (such as power sources,
ground circuits, switches or major connectors)
What resources you should use
Whenever appropriate, you should use the following
resources to assist in the diagnostic process:
• Service manual
• Technical equipment (for data analysis)
• Experience
• Technical Assistance
• Circuit testing tools
5d. Intermittent Diagnosis
By definition, an intermittent problem is one that does
not occur continuously and will occur when certain
conditions are met. All these conditions, however, may
not be obvious or currently known. Generally,
intermittents are caused by:
• Faulty electrical connections and wiring
• Malfunctioning components (such as sticking relays, solenoids, etc.)
• EMI/RFI (Electromagnetic/radio frequency interference)
• Aftermarket equipment
Intermittent diagnosis requires careful analysis of
suspected systems to help prevent replacing good
parts. This may involve using creativity and ingenuity to
interpret customer complaints and simulating all
external and internal system conditions to duplicate the
problem.
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.

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ENGINE DRIVEABILITY AND EMISSIONS 6E–65
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 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:

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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

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