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Home >> Ford >> 2012 >> Mustang V8-5.4L SC >> Repair and Diagnosis >> Restraints and Safety Systems >> Air Bag Systems >> Testing and Inspection >> Initial Inspection and Diagnostic Overview >> Principles Of Operation

Principles Of Operation




Air Bag and Safety Belt Pretensioner Supplemental Restraint System (SRS)

Principles of Operation

The Restraints Control Module (RCM) continuously receives/monitors all inputs from the following Supplemental Restraint System (SRS) components:

- Front impact severity sensor (frontal restraints sensor)

- First row side impact sensor (mounted on inner rocker panel) (left/right side restraints sensor 1)

- Safety belt buckle switches (driver and passenger)

- Driver seat track position sensor

- Occupant Classification System Module (OCSM)

If the RCM (Restraints Control Module) detects sudden vehicle deceleration and/or lateral deceleration based on the information received from all sensors and switches and determines that deployment is required, the RCM (Restraints Control Module) sends voltage and current to deploy the appropriate SRS (Supplemental Restraint System) components.

During a frontal or side crash, the RCM (Restraints Control Module) may deploy the following SRS (Supplemental Restraint System) components, based on crash severity and sensor input.

- Safety belt retractor pretensioner(s)

- Seat side air bag(s)

- Driver/passenger dual-stage air bag (one or both stages)

The fact that the safety belt retractor pretensioner(s) or air bags did not activate for both front seat occupants in a crash does not mean that something is wrong with the system.

The RCM (Restraints Control Module) performs a self-test of the complete SRS (Supplemental Restraint System) during each startup. If a SRS (Supplemental Restraint System) fault exists, the air bag warning indicator will illuminate and remain illuminated for the rest of the ignition cycle. In addition to the self-test at start up, the RCM (Restraints Control Module) continuously monitors all of its SRS (Supplemental Restraint System) components and circuitry for correct operation.

Air Bag Warning Indicator

The air bag warning indicator:

- located in the Instrument Panel Cluster (IPC) will prove out by lighting for 6 seconds and then turn off.

- will flash and/or illuminate based on the message the IPC (Instrument Panel Cluster) receives from the RCM (Restraints Control Module).

- will illuminate if the IPC (Instrument Panel Cluster) does not receive a message from the RCM (Restraints Control Module).

Air Bag Module Second Stage Deployment Check

Because the driver and passenger front air bags each have 2 deployment stages, it is possible that Stage 1 has deployed and Stage 2 has not.

If a front air bag module has deployed, it is mandatory that the front air bag module be remotely deployed using the appropriate air bag disposal procedure.

- For information on driver air bag module and/or passenger air bag module remote deployment, refer to Pyrotechnic Device Disposal Service and Repair.

Clockspring

The clockspring:

- allows for continuous electrical connections between the driver air bag module and the RCM (Restraints Control Module) when the steering wheel is turned.

Driver Air Bag Module

The driver air bag module:

- is a dual-stage air bag, upon receiving a flow of current from the RCM (Restraints Control Module) , deploying at 1 of 2 different rates depending upon vehicle impact severity and sensor input.

Event Notification Signal

In the event of a crash, the RCM (Restraints Control Module) provides an event notification signal to the fuel pump driver module(s) to disable the fuel system.

The RCM (Restraints Control Module) does not monitor the event notification signal circuit for faults and will not set a DTC if a fault occurs.

High Speed Controller Area Network (HS-CAN)

This vehicle utilizes a communication system called a High Speed Controller Area Network (HS-CAN). The RCM (Restraints Control Module) communicates with various modules for required information about the vehicle. Refer to Information Bus for information about the HS-CAN (High Speed Controller Area Network).

Impact Sensor

The SRS (Supplemental Restraint System) uses 3 satellite sensors in addition to the RCM (Restraints Control Module). The RCM (Restraints Control Module) is mounted to the center tunnel beneath the console. The front impact severity sensor (frontal restraint sensor) is located in the front of the vehicle, behind the grille mounted on the radiator support. The side impact sensors are mounted on the inner rocker panels. Mounting orientation is critical for correct operation of all impact sensors.

Occupant Classification System (OCS)

The Occupant Classification System (OCS) is found only on the front passenger seat. The front passenger seat OCS (Occupant Classification System) is comprised of a silicone gel-filled bladder mounted between the seat cushion foam and pan. An integrated OCSM (Occupant Classification System Module) with pressure sensor is attached to the bladder by a flexible hose. The integrated OCSM (Occupant Classification System Module) with pressure sensor is mounted to the seat frame. Pressure is applied to the OCS (Occupant Classification System) bladder when weight of any occupant or object in the front passenger seat is present. The pressure is then transferred through a tube and is sensed by the OCS (Occupant Classification System) pressure sensor. The OCSM (Occupant Classification System Module) communicates front passenger classification information to the RCM (Restraints Control Module) via the HS-CAN (High Speed Controller Area Network). The RCM (Restraints Control Module) uses this information when determining if the passenger air bag module is to be deployed in the event of a deployable crash. The RCM (Restraints Control Module) also uses this information for Passenger Air Bag Deactivation (PAD) indicator illumination strategy.

The OCSM (Occupant Classification System Module) monitors the OCS (Occupant Classification System) for faults.

The OCS (Occupant Classification System) is also used for operation of the passenger Belt Minder(R). For information on the passenger Belt Minder(R) feature, refer to Seat Belt Systems. To deactivate or reactivate the passenger Belt Minder(R) feature, refer to Instrument Panel, Gauges and Warning Indicators or the Owner's Literature.

Belt Tension Sensor (BTS)

The Belt Tension Sensor (BTS) :

- is a 3-wire Hall-effect sensor located at the safety belt anchor point and is part of the front passenger safety belt and retractor assembly.

- is used in conjunction with the OCS (Occupant Classification System).

The BTS (Belt Tension Sensor) is used by the OCS (Occupant Classification System) to identify the presence of a child safety seat on the front passenger seat. The BTS (Belt Tension Sensor) senses the tension on the safety belt assembly then provides an output to the OCSM (Occupant Classification System Module) , indicating that the safety belt assembly is cinched. After sensing the weight applied to the seat by the occupant and using the BTS (Belt Tension Sensor) input, the OCSM (Occupant Classification System Module) determines how the occupant should be classified and communicates the information to the RCM (Restraints Control Module). If the occupant is classified as a child, the RCM (Restraints Control Module) then automatically deactivates the passenger air bag module and illuminates the PAD (Passenger Air Bag Deactivation) indicator.

Passenger Air Bag Deactivation (PAD) Indicator

The Restraints Control Module (RCM) controls the state of the Passenger Air Bag Deactivation (PAD) indicator through a direct hard-wire connection, based on information provided by the OCS (Occupant Classification System) system. An exemption to this is when the front passenger seat is determined to be empty, and therefore indication of a deactivated passenger air bag module is not necessary. In all other cases, the PAD (Passenger Air Bag Deactivation) indicator is off when the passenger air bag module is enabled.

When the ignition is ON, the RCM (Restraints Control Module) briefly activates the PAD (Passenger Air Bag Deactivation) indicator to prove out the indicator function and verify to the front occupants correct functional operation of the PAD (Passenger Air Bag Deactivation) indicator.

The following table indicates the passenger air bag status and the PAD (Passenger Air Bag Deactivation) indicator status based on the size of the front passenger occupant.

Passenger Air Bag and Passenger Air Bag Deactivation (PAD) Indicator Status






Passenger Air Bag Module

The passenger air bag module:

- is a dual-stage air bag, deploying at 1 of 2 different rates depending upon vehicle impact severity and sensor input.

Restraints Control Module (RCM)

WARNING: If a vehicle has been in a crash, inspect the restraints control module (RCM) and the impact sensor (if equipped) mounting areas for deformation. If damaged, restore the mounting areas to the original production configuration. A new RCM and sensors must be installed whether or not the air bags have deployed. Failure to follow these instructions may result in serious personal injury or death in a crash.

NOTE: Carrying out Programmable Module Installation (PMI) will not enable the 911 assist option that is disabled.

The RCM (Restraints Control Module) carries out the following functions:

- Activates the driver, passenger and/or side air bag modules depending upon vehicle impact severity and the sensor inputs.

- Activates the driver and passenger retractor pretensioner(s) to control the tension of the driver and passenger safety belts in the event of a deployable crash

- Monitors the SRS (Supplemental Restraint System) for faults

- Sends a message to the IPC (Instrument Panel Cluster) to illuminate the air bag warning indicator if a fault is detected

- Communicates through the Data Link Connector (DLC) the current or historical DTCs

The RCM (Restraints Control Module) monitors the SRS (Supplemental Restraint System) for possible faults. If a fault is detected, the RCM (Restraints Control Module) will request the IPC (Instrument Panel Cluster) to illuminate the air bag warning indicator. When the ignition is turned OFF and then ON, the IPC (Instrument Panel Cluster) will prove out the air bag warning indicator by lighting for 6 seconds. If no faults are detected by the RCM (Restraints Control Module) , the IPC (Instrument Panel Cluster) will turn the air bag warning indicator off and it will remain off. If the RCM (Restraints Control Module) detects a fault, it will send a message to the IPC (Instrument Panel Cluster) to turn the air bag warning indicator on and it will remain on for the rest of the ignition cycle. If the RCM (Restraints Control Module) requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the IPC (Instrument Panel Cluster) will automatically activate an audible chime. The chime is a series of 5 sets of 5 tone bursts. If the chime is heard, the SRS (Supplemental Restraint System) and the air bag warning indicator require repair.

The RCM (Restraints Control Module) includes a backup power supply. This feature provides sufficient backup power to deploy the air bags in the event that the ignition circuit is lost or damaged during impact. The backup power supply will deplete its stored energy approximately one minute after power and/or ground has been removed from the RCM (Restraints Control Module).

Safety Belt Buckle Switches

The safety belt buckles are comprised of integrated circuits called Hall-effect switches. The safety belt buckle switches indicate to the RCM (Restraints Control Module) whether the safety belts are buckled or unbuckled.

The RCM (Restraints Control Module) supplies current to the safety belt buckle switch. Current flows through the switch, buckled or unbuckled to ground. The RCM (Restraints Control Module) will sense the difference in this current draw, approximately 6 mA (unbuckled) or 15 mA (buckled), and use this information in determining the deployment rate of the dual-stage driver and passenger air bag modules. If the RCM (Restraints Control Module) detects current out of this range, it will set a DTC.

The RCM (Restraints Control Module) also communicates the driver safety belt buckle switch status to the IPC (Instrument Panel Cluster) , which monitors the information to control the safety belt warning indicator. For information on the safety belt warning indicator, refer to Instrument Panel, Gauges and Warning Indicators.

Safety Belt Retractor Pretensioner

Safety belt retractor pretensioners are pyrotechnic devices integrated to the safety belt retractor assemblies. Safety belt retractor pretensioners control the tension of the driver and passenger safety belts in the event of a deployable crash.

Seat Track Position Sensors

The seat track position sensors are comprised of integrated circuits called Hall-effect switches. The seat track position sensors indicate to the RCM (Restraints Control Module) the position of the driver and passenger seat. The RCM (Restraints Control Module) uses this information in determining the deployment rate of the dual-stage air bag modules.

Secondary Air Bag Warning (Chime)

The secondary air bag warning chime is an audible chime located in and controlled by the IPC (Instrument Panel Cluster). If a fault is detected with the air bag warning indicator, a DTC will be stored in memory of the IPC (Instrument Panel Cluster). Upon receiving the message from the RCM (Restraints Control Module) that a SRS (Supplemental Restraint System) fault has been detected, the IPC (Instrument Panel Cluster) will sound the secondary air bag warning chime in a pattern of 5 sets of 5 beeps.

Seat Side Air Bag Module

The side air bag module is mounted in the seat backrest and will deploy upon receiving a flow of current from the RCM (Restraints Control Module).

Fault PIDs

There are 2 types of fault PIDs that can be reported by the OCSM (Occupant Classification System Module). 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 is 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 B2909 (BTS (Belt Tension Sensor) Fault). DTC B2909 can have up to 3 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 fault PIDs, 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.

While the RCM (Restraints Control Module) does not utilize fault PIDs for this vehicle, the OCSM (Occupant Classification System Module) has fault PIDs for certain faults.

Prove Out Procedure

Turn ignition from OFF to the ON position and monitor the air bag warning indicator with all SRS (Supplemental Restraint System) components connected. The IPC (Instrument Panel Cluster) will illuminate the air bag warning indicator continuously for approximately 6 seconds and then turn off. If a SRS (Supplemental Restraint System) fault is present, the air bag warning indicator will:

- fail to light.

- remain lit continuously.

- flash.

The air bag warning indicator may not illuminate to indicate a fault is present 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 (Restraints Control Module) to complete the testing of the SRS (Supplemental Restraint System). If the air bag warning indicator is inoperative and a SRS (Supplemental Restraint System) fault is detected, 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.
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