Ignition Circuit, Safety System (Airbag)

Ignition Circuit, Safety System (Airbag)

The ignition capacitors provide the ignition firing power in the event of a crash. The ignition circuits are only activated if two different airbag sensors detect the corresponding threshold values.

Principle procedure for checking an ignition circuit
1. Check lines and plug connections between following components:
- Airbag control unit
- Gas generator (see fault memory)

2. Disconnect any one of the plug connections between the airbag control unit and gas generator. Use the suitable adapter to measure the resistance of the gas generator.
- Setpoint resistance value :1.6 Ohms - 5.6 Ohms
- Setpoint resistance value:2.1 Ohms - 5.6 Ohms (driver's airbag interval stage 1 or interval stage 2)

3. If the tests at 1. and 2. return the state OK, check the airbag control unit.

NOTES:
- There is a short circuit bridge at the gas generator or at the gas generator connector.
- Check the resistance using the diagnosis system measuring technique (or a BMW-approved multimeter), there is otherwise the risk of airbag deployment.
- For the driver's airbag, the clock spring conductors and the poor contact to the this component are a great source of faults. For this reason, the clock spring conductors must be checked for continuity (simultaneously turning the steering wheel).
- Meaning of "Ignition circuit short circuit": short circuit between the lines from two different ignition circuits.
- Particularly in the case of sporadic faults (i.e. fault currently not present), the problem may be attributed to poor contacts, corrosion or loose contacts in the plug connection.
- Use the fault memory to determine which gas generator is involved. If, for example, the fault memory contains "93B0 head airbag", the gas generator for "head airbag" is involved. Consult the wiring diagram for the pin numbers and adapter numbers.

WARNINGS:
All work on the airbag must only be conducted with the battery disconnected.
Connect and disconnect control unit, sensors and inflator assemblies (gas generators) only with the battery disconnected.
The airbag control unit contains vehicle-specific data and must therefore be encoded before start-up. Removal and installation into other vehicles is prohibited.