Diagnostic Instructions
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Diagnostic Instructions
The symptom chart can be used to help locate SRS concerns if no DTCs are retrieved and the listed symptoms are observed. Whether or not the listed symptoms are observed, always carry out the following:
1. Run the Self Test to determine what on-demand and continuous memory DTCs are being sensed by the RCM and OCSM.
2. Retrieve all SRS DTCs and fault PIDs stored in the RCM and OCSM memory.
3. If on-demand DTCs are different than continuous memory DTCs, always diagnose the on-demand DTCs first.
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.
Self-Test/Continuous Memory and Clear DTCs
During vehicle operation, the RCM and OCSM will detect and store both intermittent and hard failure DTCs in non-volatile 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 time-outs vary with each DTC and module.
Once 75 hours of operation have been recorded by the RCM and/or the OCSM since the concern was last detected, all RCM and/or OCSM CMDTCs will automatically be removed from memory.
Lamp Fault Codes (LFCs)
This vehicle supports Lamp Fault Codes (LFCs) only when the RCM is in plant mode, a rapid flash of the air bag warning indicator. A new RCM installed to a vehicle will be in plant mode until:
- Programmable Module Installation (PMI) has been carried out.
- the RCM sees a fault-free SRS (no DTCs present).
If a LFC is present after completing PMI, a fault is present in the SRS and on-demand DTCs must be retrieved and diagnosed.
Bit-Mapped DTCs
Many of the continuous memory and on-demand DTCs that can be present in the RCM/OCSM provide general fault information and require accessing the bit-mapped PIDs (fault PIDs) to identify the specific concern. DTCs that use fault PIDs are conceptually different from conventional DTCs.
Conventional DTCs identify a specific concern for a given component and point to a particular diagnostic path. In the diagnostic path, PIDs are sometimes used to determine the root cause.
DTCs that use fault PIDs do not identify the specific concern. The DTC identifies the component(s) or type of components in which the concern exists. The next level, fault PIDs, identifies the specific device and fault condition. Fault PIDs are available for both on-demand (active) and continuous memory (historic) DTCs. Those associated PIDs are an extension of the information provided by the DTC and are identified by the same DTC number. Using both DTC and the fault PID is necessary to define the specific fault present (in the same manner as normal DTCs).
A scan tool must be used to view DTCs and their fault PIDs. Once a scan tool has retrieved a DTC, use the scan tool to view the fault PIDs. Viewing the fault PIDs must be carried out to identify the specific concern that is present. When the viewing of fault PIDs has been carried out, the scan tool can display the PIDs associated with that DTC, including the status or state that exists (on-demand DTC) or existed (CMDTC). Refer to the manufacturer's instructions for the scan tool being used on how to view fault PIDs.
Fault PIDs
There are 2 types of faults that can be reported by the RCM and or OCSM. The first type, considered conventional, has only one level of fault reporting and identifies a specific concern for a given component and points to a particular diagnostic path (for example, DTC B1317 [Battery Voltage High]).
The second type uses a process within the software of the controller that maps the byte and bit to name a specific device and fault condition. This process is called Bit-mapping and referred to as fault PIDs in the diagnosis of the vehicle. This type does not identify the specific concern or component on the first level of fault reporting (for example: DTC B2293 [Restraint System - Airbag Fault]). DTC B2293 can have up to 28 specific on-demand fault PIDs (areas of concern) associated with this DTC.
Those associated fault PIDs are an extension of the information provided by the DTC and are identified by the same DTC number. A scan tool must be used to view DTCs and their fault PIDs. Once a scan tool has retrieved a DTC, use the scan tool to view the fault PIDs. In the diagnostic path, other types of PIDs are sometimes used to determine the root cause (for example, resistance or voltage PIDs).
When viewing of fault PIDs has been carried out, the scan tool can display the PIDs associated with that DTC, including the status or state that exists (on-demand [active] DTC) or existed (continuous memory [historic]) DTC. Refer to the manufacturer instructions for the scan tool being used on how to view fault PIDs.
Deployment Loop
The deployment loop is made up of the RCM, deployable device, air bag(s), safety belt pretensioners (safety canopies, deployable steering columns, load limiting retractor, adaptive tether, adaptive vent, if equipped) and associated circuits and input from various sensors throughout the vehicle. Each deployable device contain an initiating device called a squib. Air bag/safety canopies modules can contain more than one squib, some vehicles may have up to 4 squibs in one air bag module. A squib (igniter) is a device designed to convert electrical energy to the heat energy necessary to deploy a pyrotechnic restraints system device. Squibs are often referred to as loops during the diagnostic process.
Prove Out Procedure
Turn the ignition from the OFF to the ON position and visually monitor the air bag warning indicator with all SRS components connected. The air bag warning indicator will light continuously for approximately 6 seconds and then turn off. If an SRS fault is present, the air bag warning indicator will:
- fail to light.
- remain lit continuously.
- flash.
The air bag warning indicator may not illuminate until approximately 30 seconds after the ignition has been turned from the OFF to the ON position. This is the time required for the RCM to complete the testing of the SRS. If the air bag warning indicator is inoperative and an SRS fault exists, a chime will sound in a pattern of 5 sets of 5 beeps. If this occurs, the air bag warning indicator will need to be repaired before diagnosis can continue.