Audi Coupé B4 8B airbag control unit repair

What is an Audi Coupé B4 8B airbag control unit?

The airbag control unit is the central control unit of the restraint system (SRS) in the Audi Coupé B4 8B. It evaluates the signals from the crash sensors and, within milliseconds of an impact, decides which airbags and seatbelt pretensioners fire. If there has been an accident, the unit stores crash data and locks itself.

When you turn the ignition key, the airbag warning light comes on briefly and then goes out again. Behind this is the unit's self-test: it queries sensors, squib circuits and wiring. If the light stays on, it has detected a fault.

The unit also keeps the whole system under watch while you drive. It is fitted in the Audi Coupé B4 8B (1991 to 1996) and comes from Bosch. You should take an illuminated warning light seriously, because then it is not certain that the airbags will deploy as intended in an emergency.

Why is the Audi Coupé B4 8B airbag control unit defective?

Most often the cause is crash data stored in the unit after an accident, even if no airbag has deployed. Ageing components, cold solder joints, moisture and corrosion on the connectors, as well as voltage spikes, for example from a weak battery or a jump start, are other possible causes.

These crash data cannot be removed with an ordinary diagnostic tool.

How to recognise a fault: the airbag warning light stays on, the fault memory cannot be cleared, or the diagnostic tool finds no contact with the control unit at all. Electronics also age. Over many years, temperature fluctuations can crack solder joints and shift the values of individual components.

If moisture reaches the housing or the connector, corrosion attacks the contacts. The result is faults that at first often occur only occasionally.

Common error codes for Audi Coupé B4 8B airbag control unit repair

The stored codes point to problems in the squib circuits, in the power supply or in the control unit itself. They are read out with a diagnostic tool, and they narrow down which part of the system the fault lies in.

These codes are known in connection with the airbag control unit of the Audi Coupé B4 8B. The list makes no claim to be complete.

• 65535 → Internal control unit fault
• 00532 → Supply voltage too low, sporadic
• 00588 → Driver airbag squib circuit, resistance fault
• 00589 → Front passenger airbag squib circuit, resistance too high
• 00590 → Front passenger airbag squib circuit, second stage faulty
• 01217 → Driver-side side airbag squib circuit, resistance fault
• 01218 → Front passenger-side side airbag squib circuit, resistance fault

A code that has been read out does not, on its own, prove that the control unit is defective. The cause can equally be a connector, wiring or an airbag module. Only the inspection shows where the fault really lies.

Write down the codes or print the read-out report and enclose it with the unit. During the inspection this helps to place the fault more accurately.

What part numbers are available for the Audi Coupé B4 8B airbag control unit repair?

On the label of the control unit you will find the part number, which defines its exact version. Within a model series, different numbers exist depending on equipment and year of manufacture.

These part numbers are known for the Audi Coupé B4 8B. The list is not complete.

• 8A0959655A
• 8A0959655B (Bosch)
• 8A0959655C (Bosch)

Hold the number on your unit next to this list. This only tells you whether it is the matching unit. Whether it is defective is clarified only by reading out the fault memory or by our inspection.

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

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.