Component Tests and General Diagnostics

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.

Checking the ignition circuit
1. Check lines and plug connections between following components:
- Airbag control unit
- Alternator: see fault memory

2. Disconnect any one of the plug connections between the airbag control unit and alternator. Use the suitable adapter to measure the resistance of the alternator.
- 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, replace the airbag control unit.

NOTE:
- There is a short circuit bridge at the alternator or at the alternator connector.
- Test the resistance using the Tester measurement system, otherwise danger of airbag operation.
- 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 firing circuit disconnected: short circuit between the lines from two different ignition circuits.
- In the case of sporadic faults in particular (i.e. fault not present at the moment), the fault is the result of poor contact, corrosion or a loose contact of the plug connection.
- Use the fault memory to determine which generator is involved. If, for example, the fault memory contains "930984 head airbag", this is the "head airbag" alternator. Consult the wiring diagram for the pin numbers and adapter numbers.

NOTE: 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 in other vehicles is prohibited.