The RCM is located under the floor console, near to the gearshift lever. Installation marks on the module are to make sure it is aligned correctly.
A micromechanical crash sensor is incorporated into the RCM; this measures the vehicle's acceleration/deceleration in the event of a collision. The calculated value is evaluated by the RCM to determine the severity of the impact.
The RCM compares the values it receives from the crash sensor, the side impact sensors and the internal micromechanical sensor. If the deceleration due to a frontal or side impact exceeds a stored value then the RCM triggers the air bags and safety belt pretensioners as required.
If the vehicle battery is destroyed in the collision, a voltage hold circuit in the RCM will still enable the air bags to be triggered up to 150 ms after the start of the impact.
If a system fault is detected by the RCM, the air bag warning lamp comes on. The fault can be located by carrying out a diagnostics check using the Worldwide Diagnostic System (WDS).
The RCM can be used again after a collision for up to 5 times, provided that the RCM is not physically damaged and that it passes a self-test.
The air bags are triggered by a direct current signal.
Crash sensor
The crash sensor is installed at the front of the vehicle, behind the radiator grille. Data from the crash sensor is evaluated by the RCM to assess the severity of a frontal impact. The crash sensor transmits digitally encoded acceleration information to the RCM.
Power is supplied to the sensor by the RCM. If a sensor fails, the RCM stores a Diagnostic Trouble Code (DTC).
Continued use of the crash sensor is permissible provided it has not been physically damaged and it passes a self-test.
The external shape of the crash sensor prevents it from being installed incorrectly.
Side impact sensors
The driver and passenger air bags are two-stage air bags. If the deceleration in a frontal impact exceeds a stored value then the first stage gas generator is ignited, followed by the second stage.
The time delay between stage one and stage two depends on the severity of the impact.
This time delay determines how quickly the air bag is inflated and how much gas it is filled with. It can be filled to between 70% and 100% of its total volume.
If during a crash it is not necessary to ignite the second stage to protect the occupants, the second stage will nonetheless be triggered at the latest 100 ms after the first stage. This is a safety measure designed to prevent accidental deployment during subsequent rescue operations.
Clockspring
The clockspring is designed to carry signals between the RCM and the driver air bag module. The clockspring is installed on the steering column, and consists of fixed and moving parts connected by a coiled Mylar tape with internal conducting tracks. The Mylar tape is able to 'wind up' and 'unwind' as the steering wheel is rotated, maintaining electrical contact at all times between the RCM and the driver air bag module.
Vehicles with stability assist have a steering wheel rotation sensor as an integral part of the clockspring.
Passenger air bag deactivation
A PAD switch can be fitted by the dealer as an optional extra; the switch is installed in the glove compartment. The driver can operate the PAD switch with a key to deactivate the passenger air bag.
When the ignition is switched on, a warning lamp in the instrument panel indicates to the driver and passenger that the passenger air bag has been deactivated.
After installing a PAD switch kit, the RCM must be re-configured using WDS.
Side air curtains and side air bags
Side air curtains
The side air curtains are located in the roof rail between the A-pillar and C-pillar. They are attached to the upper part of the side panel and are hidden behind the vehicle trim panels.
The electrical connections are located on the C-pillar at the rear end of the roof in front of the liftgate.
In the event of a side impact the relevant side air curtain is deployed and forms a protective cushion between the corresponding side window and the head of the person(s) sat on the front and rear seat.
The side air curtains are deployed simultaneously with the side air bags.
Side air bags
The side air bags are incorporated in the front seat backrest; a sewn-on label on the respective backrest indicates the vehicle is equipped with side air bag modules.
When a side air bag is deployed, the seam of the seat cover tears open enabling the air bag to inflate unhindered from the front seat backrest.
Safety belt buckle and pretensioners
The pyrotechnic pretensioners for the driver and front passenger safety belts are incorporated into the safety belt buckle stalks.
The driver's safety belt buckle has a switch for the safety belt monitoring facility, which is required by law in some markets.
The switch is connected with the RCM by means of a wiring harness.
In an accident, the safety belt pretensioners can be deployed in one of two ways:
- On their own.
- Simultaneously with the first deployment stage of the front air bag module(s).
