Diagnostic Methods
Effective Diagnostic Techniques
NOTE: Do not use this document in place of Ford-prescribed Symptom Based Diagnostics or Workshop Manual diagnostics. Diagnostic Methods is intended to provide Ford vehicle diagnostic information only for support of Ford-prescribed diagnostics.
The following diagnostic process is critical for consistently successful diagnoses. Random methods work inconsistently and often lead to multiple repairs and the accompanying frustration.
Understand and verify the symptom .
Understanding a symptom requires understanding normal operation. Duplicate the concern. Recreate the same conditions that demonstrated the original concern (road testing may be necessary).
Determine the responsible system .
Gather data, such as a visual inspection and an OASIS report. Perform system tests, such as pressure tests or DTC retrieval.
Identify the responsible component .
Test the suspect component and related parts.
Determine the root cause
Examine related components (wiring faults, misalignments, incorrect adjustments) that may be the actual cause or may have caused the component failure. Repair all related faults to avoid repeat failures. Verify the repair has corrected the concern (and not created any new ones) using the identical conditions that demonstrated the original concern.
Diagnostic Scan Tool Testing
Network Test
Performing a network test is always recommended for analysis of electronic system concerns. Always solve network issues before addressing individual symptoms or DTCs.
Recommended Practices: Refer to section 418-00 Module Communications Network, Diagnosis and Testing, to diagnose a network outage or no response from an individual module (or modules).
Diagnostic Trouble Code Retrieval
Generally, a good diagnostic strategy is to resolve all on-demand codes related to the system concern. Retrieving all continuous DTCs can also be beneficial to understand historic issues or issues outside of the suspect system that may be affecting your concern. On-demand testing should be done to ensure the fault represented by a continuous DTC is still present.
Continuous Memory Diagnostic Trouble Codes
Modules that produce diagnostic trouble codes have a program that evaluates system conditions, normally while the vehicle or system is in use. Module inputs can be checked for values indicating an electrical fault with the monitoring circuit or component. Module outputs can be monitored for correct function. Codes are stored when predefined limits are exceeded and retained even if the ignition is turned off (generally a DTC is retained for 40+ ignition cycles). Not all continuous codes have a matching on-demand code - and vice versa. This varies with different modules. For example, some network communication codes are continuous only. It is important to note that the presence of a continuous DTC does not guarantee that the fault currently exists.
Clearing Continuous Memory Diagnostic Trouble Codes
Continuous Memory DTCs caused by the issue being repaired or created during the diagnosis and repair must be cleared or they will confuse future diagnosis. NOTE: Do not clear DTCs from unresolved vehicle issues.
2016 Mustang workshop publication supplied to Mustang Atlas. Original technical text and illustrations; HTML formatting by Mustang Atlas. Source page numbering is retained for traceability. Follow the configuration, revision, warnings, and cross-references in the material. About this edition.