Diagnostic Instructions
Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)
Diagnostic Instructions
The symptom chart can be used to help locate Supplemental Restraint System (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. Retrieve all DTCs stored in the Restraints Control Module (RCM) memory. Refer to Retrieve/Clear Continuous DTCs.
2. Run the On-Demand Self Test to determine what DTCs are currently being sensed by the RCM.
3. If on-demand DTCs are different than continuous memory DTCs, always repair 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 Restraints Control Module (RCM) 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.
Once 128 key cycles have been recorded since the concern was last detected, the DTC will automatically be removed from memory.
Lamp Fault Code (LFC)
When the Restraints Control Module (RCM) detects a system fault, it will flash a coded sequence which is called a Lamp Fault Code (LFC) on the air bag warning indicator located in the Instrument Cluster (IC) module. The code is 2 digits. The first digit is flashed with a 0.5-second interval between pulses. There is a 2-second pause before the second digit is flashed, which also has a 0.5-second interval between pulses. There is a 5-second pause between each display of an LFC.
Each LFC is flashed 3 times after which the air bag indictor will remain lit for the remainder of the key-on cycle (except for DTC B2792 [cross link between firing loops] which only flashes one LFC). If there are multiple LFCs, each LFC will flash in order of priority.
Fault PIDs
There are 2 types of fault PIDs that can be reported by the Restraints Control Module (RCM). 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, 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, 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 (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.
Prove Out Procedure
Turn the ignition from the OFF to the ON position and monitor the air bag warning indicator with all Supplemental Restraint System (SRS) components connected or restraint system diagnostic tools installed. 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 flashing might not occur until approximately 30 seconds after the ignition has been turned from the OFF to the ON position. This is the time required for the Restraints Control Module (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.