System Fault Strategy

System Fault Strategy

No single fault may cause an unexpected deployment. The controller will supervise the pretensioner electrical system in order to warn the driver should a fault occur. Any fault detected by the self diagnostics shall cause the SRS/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 DC/DC 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 is 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.

WARNING: Do not make any electrical measurements on the pretensioner squib. Electrical measurement devices can induce sufficient voltage to cause unintentional firing of the pretensioner assembly

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.

Assembly/Removal/Service Instructions

WARNING: In the event of a vehicle impact where the airbags and the seatbelt pretensioner (if fitted) are deployed, the following actions MUST be performed:

Check the condition of the seatbelts, steering wheel, steering column, all connections to airbags, and the column switchgear connectors for integrity and damage. If in any doubt, replace suspected parts for new parts.

Replace both crash sensors, the safing sensor and the seatbelt pretensioner module (if fitted).

On completion of all repair procedures, switch on the ignition and check that the Airbag/SRS warning light comes on when the ignition is switched on and extinguishes after approximately six seconds indicating satisfactory completion of the airbag and pretensioner system self tests.

Vehicles for the North American, Australian and Japanese markets are fitted with drivers seat belt pretensioner systems and are fitted with a shorting plug in the yellow connector adjacent to the pretensioner control module. Vehicles for other markets do not have drivers seat belt pretensioners fitted but have a blanking plug in the yellow connector adjacent to the pretensioner control module.