Drivers side airbag is standard on all models, passenger airbag is either optional or standard depending on markets.They can be deployed by unskilled working and they are pretty expensive to replace. And this MUST be done by an authorised dealer as he's the only one who can reset the ECU. There are some procedures you must respect when working on or near he system:
1. Take off the ignition keys
2. Remove battery connectors- according to LR remove first - and than + (why?)
3. Wait for 10 minutes. This allows the condensers who activate the system to discharge completely.
There are some other rules too:
Never replace a component of this system which one from another car.
Never cut, repair or shorten an electrical cable of the system.
Never disassemble a piece of the airbag system or the belt pretensioners.
Removed parts must be stocked in the trunk of the car they come from.
When you carry them, always direct the metallic base AWAY from you.
Store parts in a cold and dry environment. (How does this go with the "trunk rule"?)
Always disconnect the battery before welding.
NEVER use a multimeter or similar universal instrument on any component, only use the TestBook.
Remount the parts carefully and torque down with a torque wrench.
If you replace a part of the system, LR insists on new mounting hardware.
If an airbag has been triggered remember some parts can be hot for up to 30 minutes.
After an accident strong enough to trigger the airbags and tensioners, the whole system must be replaced ...the wiring loom included. Great news, as, contrary to previous systems, the SRS cables are now partly wrapped together with the standard wiring loom.
All cables related to the SRS system are either in a yellow plastic sleeve or wrapped with yellow tape.
The impact sensor as well as the mechanical safety backup are both inside the DCU (Diagnostic Control Unit). Only a predefined shock can trigger both, so the DCU can send the "GO" signal simultanously to the airbags and belt tensioners. The DCU also contains condensers who stock enough energy to trigger the system safely even if the battery has already been smashed. They also supply the DCU for 150 ms with energy- enough to stock the codes and everything else in its memory before shutting down. These codes can NOT be altered or even read by the TestBook if the system has been deployed but the unit has to be sent back to Landrover to access the datas. Hey boys, this is a temperproof note on how the accident happened!
Contrary to some other manufacturers you can continue to drive after the system has been triggered. No further deployment is possible and the SRS warning light stays on. As on how far this is a good idea is not known as every shock strong enough to trigger the system will most likely wreck one or more important systems.
The drivers side airbag is fixed by 2 6mm torx bolts. They must be replaced by new parts if dismounted. The drivers airbag holds 55 liters, the passenger airbag 123 liters. If deployed the break along the predefined lines in the cover. The charge is not harmfull to people nor is it hot in contact with the driver/passenger. However it stinks. Reported "clothes burning" after an airbag deployment was always traceable to gases trapped in the clothes and visible when evaporating.
Every new Discovery has belt tensioners. They serve to give an exact pretension on the safety belts- a lot more than usually accepted for comfort. They do this in the same way as the airbags- with a pyrotechnic load. So don't mess around with them. However they don't have their own triggering, they get the command from the DCU. The load is below the floor and is connected by a cable to the belts base. If activated they give an exact tension on the belt by retracting the base.