Air Bag and Safety Belt Pretensioner SRS

AIR BAG AND SAFETY BELT PRETENSIONER SUPPLEMENTAL RESTRAINT SYSTEM (SRS)

The air bag supplemental restraint system (SRS) is designed to provide increased collision protection for front seat and second row outboard occupants in addition to that provided by the three-point safety belt system. Safety belt use is necessary to obtain the best occupant protection and to receive the full advantage of the SRS.

This vehicle line contains dual stage deployment (advanced restraint system) driver and front passenger air bag modules. These vehicles can also be equipped with optional safety canopies that deploy from the A-pillar to the C-pillar upon a side impact or if a rollover condition is detected. If equipped with safety canopies, a unique restraints control module (RCM) is used.

Air Bag And Safety Belt Pretensioner Supplemental Restraint System (SRS) Deployable Components:

See the illustration for deployable component location.

Air Bag And Safety Belt Pretensioner Suppleinental Restraint System (SRS) Sensor Components, Part 1:

Air Bag And Safety Belt Pretensioner Suppleinental Restraint System (SRS) Sensor Components, Part 2:

See the illustration for sensor component location.

Driver Air Bag Module
The driver air bag module:
- is installed new as an assembly.
- is mounted in the center of the steering wheel.
- cannot be interchanged between Expedition and Navigator vehicles.

Clockspring
The clockspring:
- is mounted on the steering column, behind the steering wheel.
- allows for continuous electrical connections between the driver air bag module and the restraints control module (RCM) when the steering wheel is turned.

Passenger Air Bag Module
The passenger air bag module:
- is installed new as an assembly.
- is mounted in the passenger side of the instrument panel.
- cannot be interchanged between Expedition and Navigator vehicles.

Safety Canopy Module
Some vehicles can be equipped with optional safety canopies for protection during side impacts or rollovers.

Vehicles equipped with safety canopies require a specific headliner. When installing a new headliner on a vehicle equipped with safety canopies, make sure a headliner for safety canopies is being used. The word "AIRBAG" will appear on the headliner where it meets each B-pillar trim panel.

The safety canopy module:
- is installed as an assembly.
- is mounted above the headliner.
- attaches from the A-pillar frame to the C-pillar frame.
- is standard equipment on the Navigator and optional on the Expedition.
- cannot be interchanged from side to side.

Safety Canopy Bridge Resistor

CAUTION: Do not deactivate the safety canopy module circuit by removing the bridge resistor from the electrical connector.

If the safety canopy bridge resistor is removed, an open circuit fault will be generated by the restraints control module (RCM).

If a restraint system diagnostic tool is installed at the safety canopy electrical connector, a low resistance fault will be generated.

The safety canopy bridge resistor:
- is equipped only on Expedition, without optional safety canopy modules.
- must not be removed during deactivation.
- can be accessed with the headliner dropped and is located just behind the RH side second row courtesy light.

Safety Belt Pretensioners
As part of the SRS, the driver and front outboard passenger safety belt buckles are equipped with pretensioners. The safety belt buckle pretensioners remove excess slack from the safety belt webbing. The pretensioners are activated by the restraints control module (RCM) when the module detects a crash event force exceeding a programmed limit.

Safety Belt Buckle Switches
As part of the supplemental restraint system (SRS), the driver and front outboard passenger safety belt buckles are equipped with safety belt buckle switches. The safety belt buckle switches indicate to the restraints control module (RCM) whether the safety belts are connected or disconnected. The RCM uses this information in determining the deployment rate of the dual-stage driver and passenger air bag modules.

Seat Track Position Sensor
The seat track position sensor is mounted to a bracket attached to the inboard side of the seat track. The seat track position sensor informs the restraints control module (RCM) of the driver seat position. The RCM uses this information in determining the deployment rate of the dual-stage driver air bag module.

Restraints Control Module (RCM)

WARNING:
- Do not handle, move or change the original horizontal mounting position of the restraints control module (RCM) while the RCM is connected and the ignition switch is ON. Failure to follow these instructions may result in the inadvertent deployment of the safety canopy and risk of personal injury.
- The restraints control module (RCM) orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) has been involved in a collision in which the center tunnel area has been damaged, inspect the mounting and bracket for deformation. If damaged, the RCM must be replaced whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.

NOTE: When installing a new restraints control module (RCM), always make sure the correct RCM is being installed. If an incorrect RCM is installed, erroneous DTCs will result.

The restraints control module (RCM) carries out the following functions:
- deploys the air bag(s) in the event of a deployable crash.
- activates the safety belt buckle pretensioners to remove slack from the safety belt.
- monitors the SRS for faults.
- illuminates the air bag indicator if a fault is detected.
- flashes the air bag indicator to indicate the lamp fault code (LFC) detected.
- communicates through the data link connector (DLC) the current or historical Diagnostic Trouble Codes (DTCs).
- signals the instrument cluster module to activate a chime if the air bag indicator is not available and another SRS fault exists.

The RCM monitors the SRS for possible faults. If a fault is detected while the ignition switch is in the ON position, the RCM will illuminate the air bag indicator located in the instrument cluster.

When the ignition is cycled (turned off and then on), the air bag indicator will prove out by lighting for six seconds and then off for two seconds. After the prove out, the air bag indicator will then flash the two-digit LFC. If an SRS fault exists, the air bag indicator will flash the LFC five times, then it will remain illuminated for the rest of the key cycle. The RCM will also communicate the current and historical DTCs through the DLC, to the scan tool. If the air bag indicator does not function, and the system detects a fault condition, the RCM will signal the instrument cluster module to activate an audible chime. The chime is a series of five sets of five tone bursts. If the chime is heard, the SRS and the air bag indicator require repair.

LFCs are prioritized. If two or more faults occur at the same time, the fault having the highest priority will be displayed. After that fault has been corrected, the next highest priority fault will be displayed.

The RCM includes a backup power supply. This feature provides sufficient backup power to deploy the front air bags and safety belt pretensioners 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 the battery ground cable is disconnected.

Electrical System
The electrical system that supports the air bag SRS:
- is powered from the battery through the ignition circuit.
- provides the electrical path from the restraints control module (RCM) to the SRS components.
- provides the electrical path from the RCM to the air bag indicator.
- provides the electrical path from the RCM to the data link connector (DLC).
- provides the electrical path from the RCM to the instrument cluster module.

Sensors

WARNING:
- The restraints control module (RCM) orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) has been involved in a collision in which the center tunnel area has been damaged, inspect the mounting and bracket for deformation. If damaged, the RCM must be replaced whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition.
- Vehicle sensor orientation is critical for correct system operation. If a vehicle equipped with an air bag supplemental restraint system (SRS) is involved in a collision, inspect the sensor mounting bracket and wiring pigtail for deformation. Replace and correctly position the sensor or any other damaged supplemental restraint system (SRS) components whether or not the air bag is deployed.

For these vehicles, the SRS Uses up to eight sensors. Within the RCM there can be up to three safing sensors which are not separately serviced. The RCM will always have at least one safing sensor for front impact. Two more safing sensors are used if the vehicle is equipped with safety canopy modules. The RCM is mounted to the center tunnel beneath the console or bench seat. All vehicles will have a front impact severity sensor that is located in the front-center of the vehicle, mounted near the bottom of the hood latch support bracket. If the vehicle is equipped with safety canopy modules, there are four additional side impact sensors external to the RCM. One front row side impact sensor is located behind each of the front door interior trim panels. One second row side impact sensor is located at the base of each C-pillar. Mounting orientation is critical for correct operation of all impact and rollover sensors.