Land Rover Discovery Owners & Service Manuals

Land Rover Discovery: Supplemental Restraint System - Component Location

Component location


Right Hand Drive (RHD) installation shown, Left Hand Drive (LHD) installation similar

Location 1 of 2

Location 1 of 2

  1. Engine Control Module (ECM)
  2. Battery
  3. Battery Junction Box (BJB)
  4. Steering column collapse actuator
  5. Clockspring (CLKSPG)
  6. Driver lower airbag
  7. Driver airbag
  8. Restraints Control Module (RCM)
  9. Central Junction Box (CJB)
  10. Passenger airbag
  11. Passenger airbag deactivation indicator
  12. Right front impact sensor
  13. Left front impact sensor

Location 2 of 2

Location 2 of 2

  1. Right impact pressure sensor
  2. Driver seatbelt retractor and pretensioner
  3. Driver side airbag
  4. Right side air curtain
  5. Right rear side impact sensor
  6. Left rear side impact sensor
  7. Left side air curtain
  8. Passenger side airbag
  9. Passenger seatbelt retractor and pretensioner
  10. Left impact pressure sensor
  11. Left front seatbelt buckle
  12. Right front seatbelt buckle


The Supplemental Restraint System (SRS) provides additional protection for vehicle occupants in certain impact conditions by selective activation of driver and passenger airbags, side airbags, side air curtains and seatbelt pretensioners. Operation of the system is controlled by a Restraints Control Module (RCM).

The RCM receives inputs from various sensors around the vehicle to determine which devices, if any, should be activated during an accident. The inputs include those from an occupant classification system for the front passenger seat (North American Specification (NAS) vehicles only), front and side impact sensors and side impact pressure sensors.

On all except NAS, Australia and Japan market vehicles, the passenger airbag can be enabled and disabled using the vehicle set-up menu in the Instrument Cluster (IC).

For additional information, refer to: Instrument Cluster (413-01 Instrument Cluster, Description and Operation).

The activation status of the passenger airbag is given by an indicator in the front overhead console. The status of the SRS is given by an airbag warning indicator in the IC.

The airbags and air curtains feature hybrid inflators, which use a selfcontained pyrotechnic device to heat a cylinder of compressed inert gas within the inflator. Above a calibrated pressure, the cylinder bursts and releases the gas into the airbag. The benefits of hybrid inflators are a cooler inflation gas, resulting in lower airbag surface temperatures, and elimination of the post-deployment effluent associated with solid pyrotechnic inflators.




The Restraints Control Module (RCM) is installed on top of the floor tunnel, under the floor console, and controls operation of the Supplemental Restraint System (SRS). The main functions of the RCM include:

  • Crash detection and recording.
  • Airbags, pedestrian protection system and seatbelt pretensioners firing.
  • Self-test and system monitoring, with status indication via the airbag warning indicator, and non-volatile storage of fault information.
  • Supply of yaw rate and lateral acceleration data for the Anti-lock Brake System (ABS) control module.

The RCM determines which elements of the SRS are to be deployed by using two internal areas:

  • Crash severity evaluation.
  • Deployment handler.

Crash severity evaluation uses data from the RCM internal accelerometer, the front impact sensors and the seatbelt buckle switches. Based on this data, the RCM decides which level of airbag module deployment is required and forwards the information to the second area, the deployment handler.

The deployment handler evaluates the status of the seat position sensors, seatbelt buckle switches and, on North American Specification (NAS) vehicles, the occupant classification system, before a final decision is made about which restraints should be deployed.

Data from the side impact and pressure sensors is used by the RCM in conjunction with acceleration data from the RCM internal accelerometer to make a deployment decision. The RCM processes the acceleration data and, subject to an impact being of high enough severity, decides whether the side airbag and air curtain should be deployed.

Yaw rate and lateral acceleration data for the ABS control module is derived from the internal accelerometer and transmitted on the High Speed (HS) Controller Area Network (CAN) chassis and powertrain buses.

On board testing of the airbags, pedestrian protection system and pretensioner firing circuits, the warning indicator circuits and the RCM status is performed by the RCM, together with the storing of fault codes. The impact and pressure sensors perform basic self-tests.

The RCM drives the airbag warning indicator via a High Speed (HS) Controller Area Network (CAN) signal. If the warning indicator fails, a fault code is recorded and a warning tone is sounded in place of the indicator if a further fault occurs. In the event of a crash, the RCM records certain data which can be accessed via the diagnostic connector.

A sensor in the RCM provides confirmation of an impact to verify if airbags, pedestrian protection system and pretensioner activation is necessary. A roll-over sensor monitors the lateral attitude of the vehicle. Various firing strategies are employed by the RCM to ensure that during an accident only the appropriate airbags, pedestrian protection system and pretensioners are fired. The firing strategy used also depends on the inputs from the seatbelt buckle switches and, on NAS vehicles, the occupant classification system.

An energy reserve in the RCM ensures there is always a minimum of 150 milliseconds of stored energy available if the power supply from the ignition circuit is disrupted during a crash. The stored energy is sufficient to produce firing signals for the driver airbag, the passenger airbag and the seatbelt pretensioners.

When the ignition is switched on the RCM performs a self-test and then performs cyclical monitoring of the system. If a fault is detected the RCM stores a related fault code and illuminates the airbag warning indicator. The faults can be retrieved by Land Rover approved diagnostic equipment. If a fault that could cause a false fire signal is detected, the RCM disables the respective firing circuit, and keeps it disabled during a crash event.



The driver airbag forms the center pad of the steering wheel. It provides head and chest protection for the driver when deployed during a frontal impact.

Lines, molded into the inner surface of the airbag cover, provide weak points that split open in a controlled manner when the airbag deploys. The driver airbag has a single stage inflator for Rest of World (ROW) and dual stage for North American Specification (NAS) markets.



The passenger airbag is located in the instrument panel, behind the upper glovebox. It provides head and chest protection when deployed during a frontal impact.

The top of the passenger airbag is attached to a channel chute underneath the top pad of the instrument panel. Doors in the top of the channel chute are forced open, and split the top pad, when the airbag deploys.

The passenger airbag has a single stage inflator for ROW and dual stage for NAS markets.



The driver lower airbag has a single stage inflator. The module has an integral door and is attached to the lower trim panel beneath the steering column. Weak points in the door break in a control manner to allow the door to hinge downward when the airbag deploys.



The side airbags are attached to the outside of each front seat backrest frame, under the backrest cover. They provide protection for the thorax, rib and pelvis when deployed during a side impact.

The side airbags are handed and each consists of a folded airbag and an inflator in a soft cover/wrapper. When the airbag deploys it fills within a deployment chute integrated into the seat trim, and splits open the airbag deployment seam in the backrest cover.



The side air curtains are installed along both sides of the car, under the edges of the headliner. They provide head protection and roll-over ejection protection for outer seat occupants, in both the front and rear of the vehicle, when deployed during a side impact.

The front and rear ends of the side air curtains are anchored to the body, to maintain tension across their lower edges of the air curtains when they deploy. Their deployment area extends between the A and C pillar trims, passing over the upper B pillar trim.



  1. Driver seat position sensor

The driver seat position sensor, a 'Hall effect' type, is fitted to the underside of the driver's seat. The sensor is actuated by the target bracket attached to the seat slide. The disturbance caused when the target bracket passes the sensor creates an output signal for the Restraint Control Module (RCM). On receipt of this signal, which indicates when the seat is forward of a defined point in its travel, the RCM disables the second stage output of the driver airbag.


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