Operation - SRS (Restraint systems)

Operation - SRS

The diagnostic and control unit (DCU) controls the SRS system. The DCU is located beneath the centre console close to the handbrake area. The DCU contains both an electronic deceleration sensor as well as an electromechanical safing sensor. When the electronic deceleration sensor within the DCU detects rapid deceleration of the vehicle, it compares the deceleration rate with stored values in its' memory. If the deceleration rate exceeds the stored value and the electromechanical safing sensor triggers, the DCU deploys the airbag and the seat belt pretensioners. The DCU will not deploy the airbags and seat belt pretensioners unless both sensors trigger.

The SRS has diagnostic capabilities through TestBook. In the event that a fault is detected, the DCU alerts the driver by illuminating a warning lamp in the instrument cluster.

The DCU controls the following: l SRS warning lamp. l Drivers airbag module. l Passenger airbag module (where fitted). l Driver seat belt pretensioner. l Passenger seat belt pretensioner.

WARNING: The integrity of the SRS system are critical for safety reasons. Ensure the following precautions are always adhered to: l Never install used SRS components from another vehicle or attempt to repair an SRS component. l When repairing an SRS system only use genuine new parts. l Never apply electrical power to an SRS component unless instructed to do so as part of an approved test procedure. l Special Torx bolts are necessary for installing the airbag module - do not use other bolts. Ensure bolts are tightened to the correct torque. l Always use new fixings when replacing an SRS component. l Ensure the SRS Diagnostic Control Unit (DCU) is always installed correctly. There must not be any gap between the DCU and the bracket to which it is mounted. An incorrectly mounted DCU could cause the system to malfunction.

System deployment

The airbag and seat belt pretensioners deploy to protect the front seat occupants when the DCU senses a rapid vehicle deceleration. The system deploys when the following conditions are met: l The ignition switch is on. l The vehicle decelerates beyond a threshold defined within the DCU. l The electromechanical safing sensor within the DCU triggers.

When all of the above conditions are met, the DCU deploys the airbag(s) and seat belt pretensioners. If the above conditions are not met, the DCU will not deploy the system.

Component replacement policy After an impact which deploys the airbags and pretensioners, the following components must be renewed: l DCU. l Driver and passenger airbag modules. l Driver and passenger buckle pretensioners. l Rotary coupler. l Flyleads (where applicable) connecting airbags and pre-tensioners to SRS harness