Firing circuit for airbag

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

Checking the ignition circuit

1. Test the plug-in connections and cables between the following components:

• Airbag control unit
  
• Generator: see fault code memory
  

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

• Nominal value of resistance: 1.6 Ohm - 5.6 Ohm
  
• Nominal value of resistance: 2.1 Ohm - 5.6 Ohm (driver's airbag stage 1 or 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 generator or at the generator connector!
  
• Test the resistance using the Tester measurement system, otherwise danger of airbag operation!
  
• For the driver's airbag, the coil spring conductors and the poor contact to the this component are a great source of faults. For this reason, the coil 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 firing 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-in connection!
  
• Use the fault code memory to determine which generator is involved. If, for example, the fault code memory contains ”93B0 head airbag”, the generator for ”head airbag” is involved. Consult the connection scheme 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 placing into operation!Removal and installation in other vehicles is prohibited!