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.
^ To verify the customer complaint, the technician should know the normal operation of the system.
2. Perform preliminary checks.
^ Conduct a thorough visual inspection.
^ Review the service history.
^ Detect unusual sounds or odors.
^ Gather diagnostic trouble code information to achieve an effective repair.
3. Check bulletins and other service information.
^ This includes videos, newsletters, etc.
4. Refer to service information (manual) system check(s).
^ "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 freeze-frame 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 1 and the J 39200 (Fluke model 87 DVOM), 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:
^ Conditions noted by the customer
^ 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 II system diagnostics. Following a repair, the technician should perform the following steps:

Important: Follow the steps below when you verify repairs on OBD II 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 Fame 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.