Ford Mustang (1999-2004) Service Manual: Diagnostic Instructions - Air Bag Supplemental Restraint System (SRS)

Special Tool(s)

Worldwide Diagnostic System (WDS) 418-F224, New Generation STAR (NGS) Tester 418-F052, or equivalent scan tool

The symptom chart can be used to help locate the air bag supplemental restraint system (SRS) concerns if no diagnostic trouble codes (DTCs) are retrieved and the listed symptoms are observed.

Whether or not the listed symptoms are observed, always perform the following.

1. Retrieve all DTCs stored in the restraints control module (RCM) memory. Refer to Retrieve/Clear Continuous DTCs in this section.

2. Run the On-Demand Self Test to determine what DTCs are currently being sensed by the restraints control module (RCM) (14B321). Refer to On-Demand Self Test in this section.

3. If the stored DTCs are different than the current DTCs, always repair the current DTCs first.

4. If memory displays different continuous DTCs than the On-Demand Self-Test, perform in the following order:

• On-Demand Self-Test.
• Memory (Retrieve/Clear Continuous DTCs).

A DTC can indicate several concerns. The DTCs are to assist in system diagnosis and are not to be considered definitive. Always refer to the pinpoint test corresponding to the DTC to determine where the concern lies and to repair the concern correctly.

The SRS diagnostics can be divided into three sections.

• Diagnostic test modes
• PID/data monitor and record
• Active command modes

Diagnostic Test Modes

Two menu options are available under the diagnostic test modes.

• Retrieve/Clear Continuous DTCs.
• On-Demand Self Test.

Retrieve/Clear Continuous DTCs

During vehicle operation, the restraints control module (RCM) will detect and store both intermittent and hard fault DTCs in nonvolatile memory. The DTC strategy employed by the RCM incorporates a time-out scheme for determining when a concern exists in the system. This requires a concern to exist for up to one minute in the system before the RCM will detect it. For the RCM to determine that a concern no longer exists, the concern must be absent for up to one minute. The actual detection timeouts vary with each DTC. The DTCs can be retrieved with a scan tool. Any DTCs stored in the RCM will be displayed on the scan tool along with a brief description of the DTC. If no DTCs are present, the scan tool will display a SYSTEM PASSED message. This option can also be used to clear DTCs from the RCM memory, as long as the concern no longer exists. Once 128 key cycles have been recorded since the concern was last detected, the DTC will automatically be removed from memory.

To retrieve or clear DTCs, follow these steps.

1. Connect the scan tool to the data link connector (DLC).

2. Turn the ignition switch to the RUN position.

3. Follow manufacturer's instructions for the scan tool being used.

4. All continuous DTCs will be displayed. Before proceeding with the clearing operation, make note of the DTCs displayed because, once cleared, they cannot be retrieved.

5. The scan tool will retrieve DTCs again after clearing DTCs and, if any remain, they will be displayed. Hard DTCs will be redisplayed after clearing DTCs since they cannot be cleared from the RCM.

On-Demand Self Test

The On-Demand Self Test option is used to verify that no electrical concerns exist with the air bag supplemental restraint system (SRS). Upon entering the self test, the restraints control module (RCM) will make an electrical check of each electrical component in the system. If a concern is detected, a DTC is displayed on the scan tool with a brief description of the DTC. Concerns detected during the self test are not stored in memory, unless the same concern was also detected during normal vehicle operation. The self test should always be run after any repair to verify that the repair was successful.

To run the On-Demand Self Test, follow these steps:

6. Connect a scan tool to the data link connector (DLC).

7. Turn the ignition switch to the RUN position.

8. Follow manufacturer's instructions for the scan tool being used.

9. The RCM will run the On-Demand Self Test and display on-demand DTCs (reflecting hard system concerns) on the screen.

PID/Data Monitor and Record

The PID/Data Monitor and Record option allows the scan tool operator to read the state of several parameter IDs (PIDs) to aid in diagnosing the system. PIDs are real time measurements of parameters such as voltages, resistances, etc., calculated by the restraints control module (RCM) and sent to the scan tool for display. Many of the PIDs supported by the RCM are calculated periodically and are, therefore, not true real time readings.

To retrieve PIDs, follow these steps:

1. Connect the scan tool to data link connector (DLC).

2. Turn the ignition switch to the RUN position.

3. Follow manufacturer's instructions for the scan tool being used.

4. PIDs are continuously updated on the display.

Active Commands

This command allows the technician to verify operation of the air bag indicator and chime. When the air bag output command is executed, the indicator and the chime are activated simultaneously for approximately four seconds. Both devices are deactivated automatically.

Restraints Control Module (RCM) Diagnostic Trouble Code (DTC) Priority Table

a - DTC: Diagnostic Trouble Code, retrieved using a scan tool.

b - LFC: Lamp fault code, flashed on air bag indicator.

c - Tone will sound only if additional DTCs are present.

Inspection and Verification

1. Verify the customer concern by checking the air bag indicator in the instrument cluster. Refer to Prove Out the System in this section.

2. Visually inspect for obvious signs of mechanical and electrical damage using the following chart:

Visual Inspection Chart

3. If the concern is not visually evident, use the scan tool to retrieve diagnostic trouble codes (DTCs) and perform the on-demand self test.

4. WARNING: The restraint system diagnostic tool is for restraint system service only.

Remove from vehicle prior to road use. Failure to remove could result in injury and possible violation of vehicle safety standards. If the on-demand self test is passed and no DTCs are retrieved, GO to Symptom Chart .

5. If DTCs are retrieved, proceed to the Restraints Control Module (RCM) Diagnostic Trouble Code (DTC) Priority Table.

Symptom Chart