- Strategy Based Diagnosis

Diagnostic Chart:

STRATEGY BASED DIAGNOSTICS
The strategy based diagnostic is a uniform approach to repair all electrical and electronics systems. The diagnostic flow can always be used to resolve a system problem and is the place to start when repairs are necessary. The steps that the technician should follow are outlined below:

1. Verify the Customer Complaint
To verify the customer complaint the technician will need to know the correct or normal operation of the system and verify the customer complaint is a deviation from normal operation. Technician should review and complete driveability and repair history worksheets. Refer to Technical Management Support and see Vehicle Inspection Forms & Symptom Checklists.

2. Preliminary Checks
^ Always begin diagnosis of engine/emission related complaints with a careful visual inspection. Refer to Computers and Control Systems / System Diagnosis / Procedures / Checking The Basics for additional information. Testing and Inspection

This step is a visual confirmation of systems or components that are malfunctioning. With the additional information gained the technician may now conduct a thorough visual inspection, consult the service history, be aware of unusual noises or odors.

^ After complaint verification and visual inspection, technicians should then perform On-Board Diagnostic System Check for diagnostic code information to further effect a good repair. Refer to Computers And Control Systems / System Diagnosis / Procedures / On-Board Diagnostic System Check. Testing and Inspection

3. Check Technical Service Bulletins and Other Service Information
Check all available service information. This includes training videos, periodical newsletters, service bulletins, PROM or system updates. Difficult to diagnose problems are often described in periodical publications by experienced technicians who have encountered like symptoms in similar vehicles.

4. Service information - System Check(s)
Most systems will have "System Checks" or "Functional Checks" that verify proper operation of the system and lead the technician on a very organized approach to diagnostics that closely follows the original development process and failure mode testing. Refer to Computers And Control Systems / Testing and Inspection / Procedures. Testing and Inspection

5. Service Diagnostics

5a. Diagnostic Trouble Code (DTC) Stored - Follow the designated DTC chart exactly to make an effective repair. Refer to Computers And Control Systems / System Diagnosis / Procedures / Diagnostic Tables. Testing and Inspection

NOTE: Do not use diagnostic trouble code charts for diagnosis unless codes are present, then use the chart(s) applicable to the code(s) displayed. All DTC charts presume the DTC failure conditions have been detected, and the code is stored.

5b. No DTC - Select the symptom from the symptom tables and follow the diagnostic paths or suggestions to complete the repair. Refer to Computers And Control Systems / System Diagnosis / Procedures / Diagnosis By Symptom. Testing and Inspection

5c. No Matching Symptom - Analyze the complaint and develop a plan for diagnostics utilizing the wiring diagrams, theory of operation, and technician knowledge combined with efficient use of available service information. Review theory of operation under Description and Operation for the suspected component or system.

5d. Intermittents - Conditions that are not always present are intermittent. These may be resolved by observing history DTC's, evaluating the symptoms and conditions described by the customer and using a check sheet or other method to pinpoint the circuit or electrical system component. Most important is to follow the suggestions for intermittent diagnosis found in the service documentation. The Tech 1, Tech 2 Scan Tools and Fluke 87 multimeter both have excellent data capture capabilities that can assist in detection of intermittents.

5e. Vehicle operates as designed/No trouble Found - This condition exists when the vehicle is found to operate normally. It is most important to verify that the condition described by the owner is normal compared to other vehicles. The condition may be intermittent so verify the complaint under the conditions described by the customer before the vehicle is released.

6. 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 found to be intermittent or normal as per 5c or 5e above.

7. Repair and Verification Tests
After a cause has been isolated, repairs should be made and validated for proper operation and verification that the symptom has been corrected. This may involve road testing or other methods to verify the complaint has been resolved under the conditions noted by the customer. Clear any stored DTCs and operate vehicle under the described problem conditions to verify DTCs do not recur.