Part 1

PRINCIPLES OF OPERATION

The supplemental restraint system (SRS) consists of a driver and passenger air bag module, safety belt pretensioners and safety canopies (containing an inflator/squib or gas generator and an air bag), impact sensors, a restraints control module (RCM), a clockspring, an air bag warning indicator lamp, occupant classification sensor (OCS) system and a passenger air bag deactivation (PAD) indicator lamp. These components are all interconnected by a wiring harness and powered by the vehicle's battery. The RCM includes a backup power supply. This feature provides sufficient backup power to deploy the SRS 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. If a SRS fault exists, the air bag warning indicator will illuminate and remain illuminated for the rest of the key cycle. In addition to the self-test at start up, the RCM continuously monitors all of its external and internal circuitry for faults.

In a frontal collision, the impact sensors located in the front of the vehicle detect the sudden deceleration and send an electrical signal to the RCM. The RCM uses the information from the impact sensors and the OCS module in the deployment determination. If the RCM determines that deployment is required, the RCM sends voltage and current to the squib(s) causing the solid chemical propellant to undergo a rapid chemical reaction. This controlled reaction produces harmless nitrogen gas that fills the air bag(s)/safety canopies and/or activates the safety belt pretensioners to remove slack from the safety belt(s).

The RCM communicates through the data link connector (DLC) the current and historical diagnostic trouble codes (DTCs) on the high-speed controller area network (HS-CAN). The RCM also communicates over the HS-CAN to the instrument cluster module, powertrain control module (PCM) and the OCS module.

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.

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

Electrical System
The electrical system that supports the air bag supplemental restraint system (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 a communication path from the RCM to the air bag warning indicator, located in the instrument cluster module, via the high speed controller area network (HS-CAN).
- provides the electrical communication path from the RCM to the data link connector (DLC) and all other modules on the HS-CAN.

High Speed Controller Area Network (HS-CAN)
This vehicle utilizes a communication system called a high-speed controller area network (HS-CAN). The HS-CAN consists of a twisted pair of wires connected to the following:
- Anti-lock brake system (ABS) module
- Instrument cluster module
- Powertrain control module (PCM)
- Transmission control module (TCM)
- Restraints control module (RCM)
- Occupant classification sensor (OCS) system
- Air suspension (vehicle dynamics module [VDM]) (if equipped)
- Data link connector (DLC)

The HS-CAN circuits use a bias voltage of approximately 2.5 volts, one is a positive 2.5 volts while the other is a negative 2.5 volts. The HS-CAN also uses 2 terminating resistors, one contained within the PCM, the other in the instrument cluster module. The terminating resistors are not serviced separately. The terminating resistors have a value of 120 ohms each, for a normal operating system total of 60 ohms. The HS-CAN will operate with only one terminating resistor and has the capability to communicate some messages to some of the control modules with only one circuit functioning, but at a reduced rate of performance. Refer to Information Bus (Module Communications Network).

Loops/Squibs
All deployable devices contain an initiating device called a squib. The squib is part of the deployment loop. Air bag/safety canopy modules can contain more than one squib, some vehicles may have up to 4 squibs in one air bag module. Squibs are often referred to as loops during the diagnostic process.

Occupant Classification Sensor (OCS) System
The occupant classification sensor (OCS) system is found only on the front passenger seat. The front passenger OCS system is comprised of the following: 4 OCS weight sensor bolts that are mounted to each corner of the seat track and an OCS module (electronic control unit) which is mounted to the electrical bracket underneath the seat cushion pan. All the components that make up the OCS system are all serviced separately. The weight of any occupant or object on the front passenger seat is electronically communicated to the OCS module.

The OCS 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.

When the front passenger seat is removed for service, the Zero Seat Weight Test must be carried out after the installation of the front passenger seat. When an OCS system component is installed new, the System Reset must be carried out after the installation of the front passenger seat. The Zero Seat Weight Test and/or System Reset must be carried out only as instructed to do so. For information on the Zero Seat Weight Test and/or System Reset, refer to Occupant Classification Sensor (OCS) System Zero Seat Weight Test or Occupant Classification Sensor (OCS) System Reset. Component Tests and General Diagnostics Programming and Relearning

In the event of a deployable crash, a new passenger seat track with OCS weight sensor bolts must be installed. Refer to Occupant Classification Sensor - Manual Seat Track or Occupant Classification Sensor - Power Seat Track. Occupant Classification Sensor - Manual Seat Track Occupant Classification Sensor - Power Seat Track

Occupant Classification Sensor (OCS) System Module
Based on programmed limits, the occupant classification sensor (OCS) module will inform the restraints control module (RCM), via a high speed controller area network (HS-CAN), of the necessary information. The RCM uses this information in determining if the passenger air bag module or passenger seat side air bag module is to be deployed in the event of a deployable collision.

The OCS module monitors the OCS system for faults and communicates on-demand and continuous diagnostic trouble codes (DTCs) via the data link connector (DLC) with the use of a scan tool.

Passenger Air Bag Deactivation (PAD) Indicator
The passenger air bag deactivation (PAD) indicator is a visual indicator used to inform the front seat occupants of the passenger air bag deactivation state. The PAD indicator is a stand-alone lamp installed into the vehicle instrument panel in a position visible to each front seat occupant.

The restraints control module (RCM) controls the state of the PAD indicator through a direct hardwire connection, based on information provided by the occupant classification sensor (OCS) system. The PAD indicator illuminates to indicate the passenger air bag module is disabled. An exemption to this is when the front passenger seat is determined to be empty and the passenger safety belt is unbuckled, therefore indication of a deactivated passenger air bag module is not necessary. In all other cases, the PAD indicator is unlit when the passenger air bag module is enabled.

When the ignition switch is in the ON position, the PAD indicator prove-out period is initiated by the RCM. The RCM briefly activates the PAD indicator to prove-out the indicator function and verify to the front occupants correct functional operation of the PAD indicator.

When the OCS module detects a fault that causes diagnostic trouble code (DTC) B2290 and/or B1013 to set on-demand in the OCS system, the OCS module sends a message to the RCM. Upon receiving the fault message from the OCS module, the RCM disables the passenger air bag module, illuminates the PAD indicator indicating the passenger air bag module is disabled and sends a message to the instrument cluster to illuminate the air bag warning indicator. The passenger air bag module will remain disabled until the cause for the on-demand DTC has been corrected. For information on the OCS system, refer to Occupant Classification Sensor System.

Passenger Air Bag and PAD Indicator Status:

The table indicates the passenger air bag status and the PAD indicator status based the size of the front outboard passenger occupant.

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

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 accidental deployment of the safety canopy and risk of serious 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, a new RCM must be installed whether or not the air bags have deployed. In addition, make sure the area of the RCM mounting is restored to its original condition. Failure to follow these instructions may increase the risk of serious personal injury or death in a collision.

CAUTION: Prior to removal of the restraints control module (RCM) module, it is necessary to upload module configuration information to the scan tool. This information needs to be downloaded into the new RCM module once installed. Refer to Information Bus (Module Communications Network).

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 diagnostic trouble codes (DTCs) will result.

The restraints control module (RCM) carries out the following functions:
- deploys the air bag(s)/safety canopies in the event of a deployable collision.
- activates the safety belt buckle pretensioners to remove slack from the safety belt in the event of a deployable collision.
- monitors the supplemental restraint system (SRS) for faults.
- sends a message to the instrument cluster module to illuminate the air bag warning indicator if a fault is detected.
- communicates through the data link connector (DLC) the current or historical diagnostic trouble codes (DTCs).

The RCM monitors the SRS for possible faults. If a fault is detected, the RCM will request illumination of the air bag warning indicator.

When the ignition is cycled (turned OFF and then ON), the instrument cluster will prove out the air bag warning indicator by lighting for 6 seconds and then off. If a current SRS fault exists, the RCM requests illumination of the air bag warning indicator and will remain illuminated for the rest of the key cycle. During that same key cycle some faults that recover, i.e. Loss of Communication with the PCM, the RCM will send a request to the instrument cluster module to turn the air bag warning indicator off IF no other fault is present. The RCM will also communicate the on-demand (current) and continuous (historical) DTCs through the DLC, to the scan tool. If the RCM requests illumination of the air bag warning indicator and the air bag warning indicator does not function, the instrument cluster module 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 and the air bag warning indicator require repair.

The RCM includes a backup power supply. This feature provides sufficient backup power to deploy the SRS in the event that the ignition circuit is lost or damaged during a collision. The backup power supply will deplete its stored energy approximately one minute after the battery ground cable is disconnected.

Safety Belt Buckle Switches
As part of the supplemental restraint system (SRS), the driver and front 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 of the dual-stage driver and passenger air bag modules.

Safety Belt Pretensioners
As part of the supplemental restraint system (SRS), the driver and front 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 collision exceeding a programmed limit.

Safety Canopy Module
Vehicles are equipped with safety canopies for protection during side impacts or rollovers.

Safety canopies require a specific headliner. 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.
- cannot be interchanged from side-to-side.

Seat Track Position Sensor
The seat track position sensor is mounted to a bracket attached to the inboard side of the driver 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 of the dual-stage driver air bag module.

Impact Sensors

WARNING: 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. Install a new and correctly position the sensor or any other damaged supplemental restraint system (SRS) components whether or not the air bag is deployed. Failure to follow these instructions may increase the risk of serious personal injury or death in a collision.

For this vehicle line, the supplemental restraint system (SRS) uses 6 satellite sensors in addition to the restraints control module (RCM). The RCM is mounted to the center tunnel beneath the console. All vehicles have 2 front impact severity sensors located in the front-center area of the vehicle, behind the grille mounted on the hood latch bracket. The first row impact sensors are mounted behind the trim panel near the floor on the B-pillar, the second row sensors are located on each C-pillar. Mounting orientation is critical for correct operation of all impact sensors.

Side Air Bag Module

NOTE:
- References to side air bag modules refer to the seat side air bag module, not to the steering wheel or instrument panel mounted air bag components of the supplemental restraint system (SRS).
- When servicing a seat equipped with a side air bag module, refer to Seats.

A side air bag module provides protection of the thorax area (between the neck and abdomen) of the body, working in conjunction with the head protection provided by a safety canopy module.

The side air bag module:
- will deploy upon receiving a flow of current from the restraints control module (RCM), initiated by the side impact sensor and internal RCM circuitry.
- is installed as an assembly.
- is mounted in the driver or passenger seat backrest.
- is used in conjunction with a safety canopy module.

Diagnostic Instructions
The symptom chart can be used to help locate 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 carry out the following:
1. Run the Self Test to determine what on-demand and continuous memory DTCs are being sensed by the restraints control module (RCM) and occupant classification sensor (OCS) module.
2. Retrieve all SRS DTCs and fault PIDs stored in the RCM and OCS modules 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. Pinpoint Tests

Diagnostic Test Options
Scan tool options:
- Self Test/On-Demand
- Self Test/Continuous Memory and Clear DTCs

Refer to the manufacturer's literature for the scan tool being used for correct scan tool test options.