Audi A6 4Z Allroad airbag control unit repair

What is an Audi A6 4Z Allroad airbag control unit?

The Audi A6 4Z Allroad airbag control unit is the central control unit of the restraint system (SRS). It continuously monitors the airbag system and, in an accident, decides within milliseconds which airbags and seatbelt pretensioners to deploy.

As soon as the vehicle starts, the unit runs a self-test. The airbag warning light comes on briefly and goes out again if all components are in order. If the control unit finds a fault, the light stays on.

In an accident it evaluates the signals from the crash sensors and triggers the appropriate airbags and seatbelt pretensioners. Afterwards it stores crash data and locks itself.

The control unit is installed in the Audi A6 4Z Allroad (2000 to 2005). It is made by Bosch.

Why is the Audi A6 4Z Allroad airbag control unit defective?

The most common cause is crash data stored after an accident, even if no airbag deployed. Other possible triggers are aged electronic components, cold solder joints, moisture and corrosion on connectors, and voltage spikes.

Stored crash data cannot be erased with an ordinary diagnostic tool. The control unit then remains locked, even if nothing on the Audi is visibly damaged. Even without an accident, components inside the unit age, and solder joints can develop hairline cracks over the years.

Voltage spikes arise, for example, from a weak battery or from jump-starting. Moisture and corrosion on the connectors can also cause malfunctions.

Typical signs are an airbag warning light that stays on permanently, a fault memory that cannot be cleared, or a diagnostic tool that cannot connect to the control unit.

Common error codes for Audi A6 4Z Allroad airbag control unit repair

The error codes for this vehicle point to faults in the squib circuits, in the power supply, or internal faults of the control unit.

The following selection shows codes that occur on this vehicle. They concern the squib circuits of the front and side airbags, the supply voltage and internal memory faults.

• 65535 → Internal memory fault in the control unit
• 00588 → Fault in the driver airbag squib circuit
• 00532 → Supply voltage too low, intermittent
• 00589 → Passenger airbag squib circuit, resistance too high
• 00590 → Fault in the passenger airbag squib circuit
• 01217 → Resistance fault, driver-side side airbag
• 01218 → Resistance fault, passenger-side side airbag

Error codes are read out with a diagnostic tool. A code alone does not prove that the control unit is defective. Connectors, wiring or an airbag module can also be the cause. Only testing shows where the fault actually lies.

What part numbers are available for the Audi A6 4Z Allroad airbag control unit repair?

The part number is printed on the label of the control unit and determines the exact version. Within a model series there are different numbers depending on equipment and year of manufacture, so it is worth checking the label before sending the unit in.

These part numbers are known for the Audi A6 4Z Allroad. The list makes no claim to completeness.

• 4Z7959655B (Bosch)
• 4Z7959655D
• 4Z7959655E
• 4Z7959655H
• 4Z7959655J
• 4Z7959655M
• 4Z7959655N
• 4Z7959655TD

Compare the number on your own unit with this list. This only confirms that it is the right unit. Whether it is defective is shown only by reading out the fault memory or by the inspection at Airbag24.

This is how you get your repair started: Have the fault memory read out, disconnect the battery and remove the control unit. Then create a repair order online and send the unit in. Processing at Airbag24, with inspection, repair and testing, usually takes 3–4 working days. Afterwards your own unit is sent back to you.

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.