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 switch is disrupted during a crash. The stored energy is sufficient to produce firing signals
for the driver air bag, the passenger air bag and the safety belt pretensioners.
When the ignition is switched on the RCM performs cyclical monitoring of the system. If a fault is detected the RCM stores
a related fault code and sends the signal to illuminate the air bag warning indicator. The faults can be retrieved by the
Land Rover approved diagnostic system. 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.
Air Bags
Hybrid Inflator Technology
All air bags feature hybrid inflators, rather than the previously used solid pyrotechnic gas generators which use an
explosion to generate the air bag charge directly. Hybrid inflators use a self-contained pyrotechnic device to heat a cylinder
of compressed inert gas within the inflator. Above a calibrated pressure, this cylinder bursts and the gas is released into
the fabric bag.
The benefits of hybrid inflators are cooler gas, hence lower bag surface temperatures, and the elimination of
post-deployment effluent associated with solid pyrotechnic generators.
Dual Stage Inflators
Both the driver air bag and passenger air bag feature dual-stage inflators. Each air bag employs two separate inflators,
fitted with independent squibs connected to the air bag. This allows air bag size, pressure and rate of rise in pressure to
be optimized to suit the vehicle's structural characteristics as well as the severity of the actual impact.
The restraint control module (RCM) monitors the severity of the collision, safety belt tension and proximity of the driver's
seat to the steering wheel in order to determine the air bag deployment strategy:
At relatively low speeds, or when smaller occupants are seated close to the steering wheel only the 'stage 1'
inflator deploys; this inflates the air bag to about 70% of its capacity.
At higher speed impacts both 'stage 1' and after a pre-set interval, 'stage 2' inflator deploys to achieve maximum
air bag volume, unless the driver is dangerously close to the steering wheel.
Driver Air Bag
The driver air bag has a two stage inflator, with separate electrical connectors for each stage. Lines molded into the inner
surface of the driver air-bag cover, provide weak points that split open in a controlled manner when the driver air bag
deploys.
Passenger Air Bag
Item
Part Number
Description
1
-
Stage one – 70% air bag volume
2
-
Stage two – full air bag volume
The top of the passenger air bag is attached to a re-enforcement lid in the instrument panel. The reinforcement lid
incorporates a single door that opens, splitting the instrument panel covering, when the air bag deploys. The air bag has a
two stage inflator, with separate electrical connectors for each stage.
Passenger Air Bag Disable Switch