Audi 100 4A airbag control unit repair

What is an Audi 100 4A airbag control unit?

In an emergency, the airbag control unit of the Audi 100 4A decides within milliseconds which airbags and seatbelt pretensioners deploy. As the central control unit of the restraint system (SRS), it evaluates the signals from the crash sensors to do so.

In a collision, the control unit uses the sensor signals to work out how severe the accident is and releases the ignition for the appropriate restraint devices. It is installed in the Audi 100 4A (1990 to 1994).

As long as nothing happens, it continuously monitors the whole system and indicates faults via the airbag warning light in the instrument cluster. If an accident has occurred, it stores crash data and locks itself.

Why is the Audi 100 4A airbag control unit defective?

Most often the cause is crash data stored after an accident, even if no airbag deployed; an ordinary diagnostic tool does not remove it. Ageing components, cold solder joints, corrosion from moisture at the connectors and voltage spikes are other possible causes.

An accident in which no airbag fires can also leave crash data behind.

Regardless of that, the electronics wear over the years: solder joints develop fine cracks, and moisture that gets in attacks the contacts of the connectors. A weak battery or jump-starting can produce voltage spikes that damage the electronics in the Audi 100 4A.

Signs of this are an airbag warning light that stays on permanently, a fault memory that cannot be cleared, or a diagnostic tool that cannot establish contact with the control unit.

Common error codes for Audi 100 4A airbag control unit repair

The known codes for the Audi 100 4A report a fault in the control unit itself, an abnormal supply voltage or a resistance fault in the firing circuits. Most of them relate to the firing circuits of the airbags.

The list below summarises codes that occur on this vehicle. They concern the condition of the unit, the power supply and the firing circuits of the driver, passenger and side airbags.

• 65535 → Control unit reports an internal fault
• 00532 → Supply voltage too low, intermittent
• 00588 → Driver airbag igniter, resistance fault
• 00589 → Passenger airbag firing circuit, resistance too high
• 00590 → Passenger airbag igniter, second firing circuit, fault
• 01217 → Driver-side side airbag igniter, resistance fault
• 01218 → Passenger-side side airbag igniter, resistance fault

Fault codes are read out with a diagnostic tool. A single code does not allow a reliable conclusion that the control unit is defective, because connectors, wiring or an airbag module are also possible causes. A check provides clarity.

What part numbers are available for the Audi 100 4A airbag control unit repair?

On the label of your control unit you will find the part number, which defines its exact version. Depending on equipment and year of manufacture, there are different numbers within one model series.

The following part numbers are known for the Audi 100 4A; this overview is not complete.

• 4A0959655

Compare the number on your unit with the overview. This only ensures that it is the right unit. Whether there is a defect only becomes clear from reading out the fault memory or from our check.

The route to repair: first have the fault memory read out, disconnect the battery and remove the control unit. Then create a repair order online and send in the unit. Checking, repairing and testing at Airbag24 usually take 3–4 working days.

The repaired control unit comes back with all vehicle data and is ready for use as soon as it is refitted — no coding or programming is required.