Strategy-Based Diagnostics
Strategy Based Diagnostics
Strategy Based Diagnostics Chart
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 E Saves time by avoiding testing and/or replacing good parts E Allows you to look at the problem from different perspectives
- Guides you to determine what level of understanding about system operation is needed:
- Owners manual level
- Service manual level
- In-depth (engineering) level
- Owners 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
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, https://www.einet.isuzu. co.jp//
- Videotapes
- Service manual
4. Perform Diagnostic Checks
What you should do
The System Checks in most 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
- Assistance to identify what systems work correctly
What resources you should use
Whenever possible, you should use the following resources to perform checks:
- Technical equipment (for viewing DTCs and analyzing data)
- Digital multimeter and circuit testing tools
- Other tools as needed
5a and 5b. Perform Diagnostic Procedures
NOTE: An estimated 40 percent of successful vehicle repairs are diagnosed with these steps!
What you should do
When directed by 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 diagnostic procedures:
- 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, 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 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 (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 extreme temperatures?
- Are there areas subjected to vibration or movement (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.
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 E 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
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 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 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 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
- information and publications