Description

Description

The DB7 seat belt pretensioner system operates the drivers seat belt pretensioner in conjunction with the Airbag system. The seat belt pretensioner control module is located under the right hand seat, beside the seat control module.

The pretensioner control module calculates changes in vehicle speed using an input signal from an accelerometer. When a collision is detected (Rapid reduction in vehicle speed) the pretensioner charge is fired using electrical energy stored in a capacitor within the pretensioner control module. Firing of the pretensioner charge applies additional tension to the drivers seat belt.

The airbag and seat belt pretensioner systems share the SRS (Airbag) warning lamp. Any fault detected by the pretensioner control module is indicated by constant illumination of the SRS (Airbag) warning lamp. Flashing of the SRS warning lamp indicates a fault in the airbag system.

Should both systems develop faults, the pretensioner system will permanently illuminate the warning lamp. This would mask the airbag system warning indication. Therefore, rectify the pretensioner fault and then retest for faults in the airbag system

The pretensioner control module can log up to 10 diagnostic trouble codes together with a time since each fault was alerted to the driver. Each fault will be identified as 'Permanent' or 'Intermittent' on the PDU diagnostic trouble codes screen.

System Connections

The Autoliv RC5 Pretensioner Control Module has an 18 pin connector featuring six shorting bridges. The mating halves of the connector may be securely locked using a double mechanical locking system.

The following pins on the control module connector are used in the Aston Martin seat belt pretensioner system:

• Pin 1 Ground
• Pin 2 SRS/Airbag Warning Lamp
• Pin 11 Drivers airbag positive
• Pin 12 Drivers airbag negative
• Pin 14 Serial communications
• Pin 15 12 volt positive feed
• Case Ground

System Fault Strategy

No single fault may cause an unexpected deployment. The controller will supervise the airbag/pretensioner electrical system in order to warn the driver should a fault occur. Any fault detected by the self diagnostics shall cause the airbag warning lamp to be activated, and in some cases the pretensioner control module to enter shutdown mode. In shutdown mode, the energy of the reserve capacitors shall be discharged to avoid unintended deployment.

As the ignition is switched on, the pretensioner controller will directly discharge the energy capacitors. When the start up procedure is completed without detecting any faults, the converter will be activated allowing the capacitors to be charged. The system shall be fully active within 11 seconds after switching the ignition on providing that no faults are detected.

All system faults monitored by the controller are filtered in software to avoid fault warnings due to transient electrical disturbances.

If a fault which could lead to inadvertent deployment be detected by the microprocessor, a software shutdown will be generated. However, a leakage to an earth or positive potential in the pretensioner output circuit shall not cause the controller to enter shutdown mode.

If a permanent short of the ignition transistor occurs, a shutdown shall be generated by the hardware circuit. If a shutdown occurs, the system shall be unable to deploy the pretensioner after a period of 3 seconds (i.e. capacitors discharged to under minimum deployment voltage).

WARNING: To avoid the possibility of personal injury caused by accidental deployment of the pretensioner, disconnect the vehicle battery and wait at least 10 minutes for all voltages to fully discharge before working on the pretensioner system. This covers the possibility of the normal capacitor discharge circuits being inoperative and failing to discharge the capacitor when instructed to do so.

If the module enters shutdown mode, all diagnostic functions are stopped, but the communications link remains active. A fault code corresponding to the cause of the problem may be read by the PDU.