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Supplementary Restraint System - SRS

The Scorpio, of course, has inertial reel belts fitted as standard, plus a fixed lap belt for a fifth passenger in the centre of the rear seat.  As additional safety, the car also has a driver airbag fitted as standard, and originally the passenger front airbag was an optional extra, later fitted as standard, while even later side impact airbags were optional. These were fitted into the upright part of the front seats. Additional protection is offered by seat belt pre-tensioners, Together these are called the Supplementary Restraint System.

It should be noted from the outset that the airbags can only be effective when the seat belts are worn.

During a severe frontal impact, the vehicle stops suddenly. At only 30mph the vehicle is covering 44 feet per second, and any body which has mass has inertia. When the vehicle stops, the passengers' inertia drives them forward until they collide with something. Without airbags, the drivers upper body crashes into the steering wheel and the fascia (Americans call this the crashpad) while his head impacts and drives a bulge into the laminated front windscreen. For the passenger who is not restricted by the steering wheel the front fascia and windscreen await to provide bone crushing injury. Almost everyone by now must have seen the crash-test dummies on high-speed film flying forwards in slow motion, jerking and threshing about as different parts of their bodies impact with the interior crushing in towards them. It is uncomfortable viewing, but necessary so that one can appreciate the forces involved.

To control the restraint system there is, of course, the control module, which is mounted behind the lower fascia to the right of the steering wheel column. This monitors the system and turns on a light in the instrument panel if it detects a fault. The module also stores fault codes for retrieval by FDS2000. The Air Bag Electronic Control Module is connected, in series, to two separate sensors, a crash sensor and a safing sensor and only if both detect a crash the ABECM (4) deploys the system. On vehicle with side impact airbags (3) a third sensor is tuned to detect side impacts (9).

The drivers airbag (1) is mounted behind the steering wheel cushion to emerge through engineered weak points on the cover. This is connected with a mylar 'clockspring' to the steering column to enable the steering wheel to turn without stressing the connections. The airbag has a 30 litre capacity and a single propellant cartridge. The passenger airbag (2), where fitted, deploys from behind the fascia airbag panel, which is designed to pop open and is restrained with a strap. The passenger has the benefit of a 60 litre bag filled from two cartridges. The airbags are fired electrically by the ABECM by an igniter built into the propellant cartridge. Note that the cartridges contain propellant rather than explosive: propellant does not explode, it converts itself into a very large volume of gas in a very brief period of time.

Because airbags are truly effective when the seat-belts are very tight, but people do not as a rule prefer to be clamped rigidly to the seat, seat-belt pre-tensioners are also used.  There are two types or pre-tensioner: one uses the inertia and/or deformation of the front of the vehicle to drive the seat-belt anchorages backward, and others use propellant. In the case of the Scorpio, where fitted, the pre-tensioners form part of the seat belt anchorage. The cable for the seatbelt catch is a friction fit through the floor mounting and ends in a closed chamber, behind which is a small propellant charge. When the system fires, the cable is forced backwards by several inches, clamping the seat belt wearer irresistibly to the seat and preventing them from gaining too much acceleration or twisting before they hit the airbag. As their name implies, the pre-tensioner only fires before or at the same time as the airbags are deployed, and never afterward.

Fault Finding

Serious injury can result by being too close to an airbag when it is deployed. Before making or breaking any connection in the system there should be a delay of at least 15 minutes after disconnecting the battery. When removing an airbag, especially from the steering wheel, keep your head away from the airbag face.

Because the igniters are fired electrically,  a circuit tester or multimeter should not be used on any Restraint System wiring.

If the airbag warning light comes on in the fascia, owner action is to checking the fuse:

Fuse 27 in the central fuse box, 10 amp

This also provides some of the power to the ABS system, so if the ABS light illuminates as well, it is probable that this fuse is at fault.

SRS Fault Codes

Fault codes are flashed by the airbag light. A single flash with a few seconds between it is Code 1. A double flash and a pause is code 2 and so on. The codes are as follows:

    1 Flash            Drivers airbag failure - or open circuit to airbag (check mylar clockspring connection)
    2 Flashes        Passenger Airbag failure - or open circuit to airbag
    3 Flashes        Failure of both airbags
    4 Flashes        Pyrotechnic seatbelt pre-tensioner failure (Either side)
    5 Flashes        Drivers airbag failure - System shorted
    6 Flashes        Passenger airbag failure - System shorted
    7 Flashes        Drivers crash sensor failure
    8 Flashes        Passenger crash sensor failure
 

The most common failure is code 1. It looks as if the light is simply flashing on and off, but if this is seen the drivers airbag mylar connector should be checked for security. After disconnecting the battery and waiting at least 15 minutes the airbag can be removed from the steering wheel by undoing the Torx screws through the rear of the steering wheel lifting the airbag off and checking the multiplug on the clockspring because this can work loose. Reconnect and reinstall the airbag fully before reconnecting the battery.

(Thanks to Darren for the Fault codes)