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Frelander 2. Manual - part 620

Seat position sensor

Passenger air bag deactivation switch

Driver safety belt buckle switch

Passenger safety belt buckle switch

Impact sensor - left-hand front

Impact sensor - right-hand front

Side impact sensor - left-hand B-pillar

Side impact sensor - right-hand B-pillar

Side impact sensor - left-hand C-pillar

Side impact sensor - right-hand C-pillar

Driver lower air bag

Adaptive steering column

Side air bag – left-hand

Side air bag – right-hand

Clockspring

Passenger air bag

Driver air bag

Curtain air bag – left-hand

Curtain air bag – right-hand

PRINCIPLES OF OPERATION

Crash Sensing

Impact sensor

The impact sensors are installed in the front and both sides of the vehicle. W hen the ignition is switched on the Restraints
Control Module (RCM), supplies power to the impact sensors which perform a self test. After satisfactory self test the
impact sensors continually output 'digital acceleration' messages to the restraints control module. The use of multiple
impact sensors provide shorter air bag trigger times through faster detection of lateral and longitudinal acceleration and
also improves detection accuracy.

Each impact sensor incorporates an accelerometer and a microchip powered by a feed from the restraints control module.
Acceleration is evaluated by the microchip and transmitted to the restraints control module, which then makes the decision
on whether or not to activate the air bags and pretensioners.

If a fault is detected the relevant impact sensor sends a fault message, instead of the digital acceleration message, to
the restraints control module. The RCM then stores a related fault code and illuminates the air bag warning indicator.
Faults can be retrieved by the Land Rover approved diagnostic system from the RCM via the high-speed CAN.

Occupant Monitoring

There are two types of occupant monitoring systems fitted to vehicles:

1. NAS markets, have an Occupant Classification Sensing System.

2. Markets except NAS and Australia, have an Occupant Detection Sensing System.

1. Occupant Classification Sensing System

Item

Part Number

Description

Safety belt tension sensor

Occupancy sensor

Occupancy sensor module

In NAS markets where safety belt use is infrequent, additional technology is used to classify the occupant of the front
passenger seat. The occupant classification sensing system provides seat load data to the Restraints Control Module
(RCM).

The occupant classification system consists of:

A pressure pad, installed under the cushion of the front passenger seat, which is connected to a pressure sensor.
A safety belt tension sensor, integrated into the anchor point of the front passenger safety belt.
An occupant classification module, installed under the front passenger seat.

The pressure pad is a silicone filled bladder. Any load on the pressure pad is detected by the pressure sensor. The safety
belt tension sensor is a strain gauge which measures the load applied by the safety belt anchor to the anchor bolt. The
sensor is located in the lower safety belt anchor point.

The occupancy sensor responds to weight changes on the passenger seat and provides an appropriate signal to the
occupancy sensor module. In addition, the belt tension sensor provides a separate input to the occupancy sensor module.
The module processes the input signals received from the sensors and forwards an appropriate signal to the RCM on the
high-speed CAN.

The RCM monitors and processes the data from these and several other sensors, before making an air bag deployment
decision. The system is designed to take account of several variables in addition to weight, including: inclination of the
vehicle and exact position and structure of the weight on the seat.

This protects against inadvertent air bag deployment, for example, if the seat were occupied by an infant in a booster

seat, or an unrestrained but very lightweight adult, in both these cases the air bag would be disabled. The occupant
classification sensing system forms part of a strategy to control passenger air bag deployment depending on the
occupancy scenario.

The occupant classification system has four possible states:

Seat Empty: the passenger air bag, passenger-side air bag and passenger safety belt buckle and pretensioner
operation is disabled; the passenger air bag deactivation indicator is not illuminated.
Occupied Inhibit: when the seat is occupied by a small person, the passenger air bag, passenger-side air bag and
passenger safety belt buckle and pretensioner operation is disabled; the passenger air bag deactivation indicator is
illuminated.
Occupied Allow: when the seat is occupied by a large person; the passenger air bag and passenger-side air bag
operation is enabled, the passenger air bag deactivation indicator is not illuminated. Passenger safety belt and
pretensioner operation status depends on the safety belt buckle status:

- active for buckled,
- inactive for unbuckled.

Error: if a system fault is detected; the passenger air bag is enabled to deploy at 'stage-1' only, refer to Air Bag
Dual Stage Inflators below. Passenger-side air bag operation is also enabled; the passenger air bag deactivation
indicator is not illuminated. Passenger safety belt and pretensioner operation status depends on the safety belt
buckle status:

- active for buckled,
- inactive for unbuckled.

Occupancy Sensor Module

The occupancy sensor module is installed on the underside of the front passenger seat. The module supplies a power feed
to the occupancy sensor and monitors the return voltage to determine if the seat is occupied or not. The result is
transmitted to the RCM on the high-speed CAN. The occupancy sensor module also monitors for short and open circuits in
the occupancy sensor. If it detects a fault, the occupancy sensor module transmits a fault message to the RCM.

Safety Belt Tension Sensor

The safety belt tension sensor is a strain-gauge type, encapsulated within the passenger safety belt anchor. The sensor
converts the force applied to the safety belt into an electrical signal. In the event that a child-seat is installed onto the
front passenger seat, the force applied to the passenger safety belt is reflected by the output signal from the sensor,
which provides data to supplement that received from the occupancy sensor. The occupancy sensor module processes the
input data and makes it available to the restraints control module, which then makes the necessary adjustments in
respect of passenger air bag deployment.

2. Occupant Detection Sensing System

The belt-minder sensor and a safety belt buckle switch are used to warn the driver if the front passenger seat is occupied
without the safety belt being engaged.

Belt Minder Sensor

The occupancy sensor is installed in the cushion of the front passenger seat between the foam padding and the cover. The
sensor consists of a foil contact circuit, embedded in a plastic sheet. Weight on the sensor reduces the resistance of the
circuit.

The safety belt buckle switch provides an output signal in response to the insertion of the safety belt tongue into the
buckle. The output signal from the switch is used by the RCM to determine whether the front seat occupants are correctly
restrained. The switch signal is used in conjunction with the belt minder sensor to ensure that air bag and safety belt
deployment only occurs when the seat is occupied.

Driver Position Sensing System

Seat Position Sensor

Item

Part Number

Description

Seat position sensor

Target bracket

The 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 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 air bag; refer to air bags section.

Control and Processing

Restraints Control Module

Internally, the Restraints Control Module (RCM) has two areas that determine which elements of the restraint system are
to be deployed:

Area 1 - Crash severity evaluation:

The first area evaluates crash severity by using data from the module's internal accelerometer, the front crash sensor and
the safety-belt buckle sensor. Based on this data, the RCM decides which level of air bag deployment is required and
forwards the information to the second area, the deployment handler.

Area 2 - Deployment handler:

The status of the seat position sensor, occupant classification sensing system and safety-belt buckle sensors are
examined before a decision is made about which restraints should finally be deployed. For instance, if the occupant
classification sensing system indicates that the passenger seat is empty, then no restraint deployment will take place on
the passenger side, even if full deployment takes place for the driver.

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