100-00 General Information 2014 Fiesta
Description and Operation Procedure revision date: 08/5/2013

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.

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 DTC s.

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 DTC s 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 DTC s 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 DTC s from unresolved vehicle issues.

Ford On-Demand Diagnostic Trouble Codes

Ford Motor Company modules have a unique feature that performs a special diagnostic program at the request of the technician (using a diagnostic scan tool). This "On-demand" diagnostic program can exercise system outputs not normally running when the car is parked and record observed faults. These diagnostic codes are communicated to the scan tool, but are not recorded in module memory. An on-demand test is an effective tool for evaluating real input and output conditions during module activity – activity that might not normally be occurring during service bay conditions. For example, an air suspension module on-demand test can run the compressor, vent the system, and observe the report from the height sensor even when the car is already at correct trim height and not requiring height adjustment.

Network Communication Diagnostic Trouble Codes

Network DTC s (U-prefix codes) are often a result of intermittent concerns such as damaged wiring or low battery voltage occurrences. Additionally, vehicle repair procedures (such as module reprogramming or diagnostics with modules disconnected) often set network DTC s. Replacing a module to resolve a network DTC is unlikely to resolve the concern. To prevent recurrence of intermittent network concerns, inspect all network wiring, especially in-line and module connectors. Test the vehicle battery to make sure the vehicle voltage will be stable.

Recommended practice: Clear the DTC and retest. If the DTC repeats, test the vehicle communication network.

DTC Nomenclature (SAE J2012 and ISO 14229)

Many modules use 5-character DTC s followed by a 2-character failure-type code. The failure-type (sometimes called "fault byte") codes provide information about specific fault conditions such as opens or shorts to ground. Continuous memory DTC s have an additional 2-character DTC status code suffix to assist in determining DTC history.

Integrated Diagnostic System Scan Tool Usage

If The Integrated Diagnostic System Scan Tool Does Not Communicate With The Vehicle Communication Module

  1. Check the Vehicle Communication Module connection and power from the DLC .
  1. Check the communication between the scan tool and the Vehicle Communication Module.
  1. Follow scan tool instructions to retry.

If The Integrated Diagnostic System Scan Tool Does Not Communicate With The Vehicle

The IDS scan tool first attempts to communicate with the PCM . After establishing communication with the PCM , the scan tool then attempts to communicate with all other modules on the vehicle.

  1. Verify the scan tool operation with a known good vehicle.
  1. Verify the ignition is ON.
  1. If an IDS session cannot be established with the vehicle, ( IDS may state "No communication can be established with the PCM"):
  1. Using the tool box menu, run the network test.

Measuring Automotive Circuits

Wiring Pin (Terminal) Fit And The Use Of Rotunda Flex Probes

Checking Power-Providing Circuits

Checking Ground-Providing Circuits

Checking Circuit Continuity

Checking For Unintended Continuity (Shorts) To Other Circuits

Checking Circuits By Back-Probing A Connector

Circuit Analysis Using Jumper Wires (Creating Substitute Circuits)

Checking Modules