Airbag control unit with part number 028 500 1106

What is the function of the airbag control unit 028 500 1106?

The BOSCH airbag control unit 028 500 1106 is the central control module for the occupant protection system in the Audi A6 C4 (model years 1994–1997). It continuously monitors data from crash sensors, processes it in real time, and is responsible for deploying airbags and seatbelt pretensioners in the event of a collision.

As the “brain” of the safety system, this control unit processes signals from various vehicle sensors. Based on this data, it determines within milliseconds whether an impact has occurred that necessitates activation of the restraint systems.

After deployment, the unit permanently stores so‑called crash data. This storage serves as a safety feature to enable post‑accident system diagnostics, but it also results in the unit being locked out of further operation until professional repair is performed.

Why does the control unit 028 500 1106 fail?

The most common cause of failure for the 028 500 1106 control unit is the retention of crash data after an accident, which locks the device. Additional faults arise from internal hardware issues caused by electrical disturbances such as undervoltage or overvoltage, short circuits, or physical damage due to moisture ingress.

Following an accident in which the airbags have deployed, the control unit becomes internally blocked. This lock often cannot be cleared via standard vehicle diagnostics (OBD2) and requires specialized chip‑level intervention.

Electronic components on the circuit board may fail due to voltage spikes in the vehicle’s electrical system—such as during jump-starts—or from age‑related wear. These failures are frequently logged in the fault memory as “control unit defective.”

External factors like moisture, for example from spilled beverages near the center console where the unit is installed, can also lead to corrosion and short circuits on the circuit board. In most cases, repair is significantly more cost‑effective than purchasing an expensive new part.

How do you recognize a defect in the 028 500 1106?

A defect in the 028 500 1106 control unit primarily manifests as a constantly illuminated airbag warning light on the instrument cluster. Communication via the OBD2 interface is often lost, and the fault memory contains error codes such as 65535 (“control unit defective”) or B1000, which cannot be cleared.

The clearest indication is the airbag warning light that fails to extinguish after starting the engine. This signals a serious fault in the restraint system that compromises vehicle operational safety.

Another clear symptom is the loss of diagnostic capability. If a specialist workshop cannot establish communication between its diagnostic tool and the airbag control unit, this strongly suggests an internal malfunction of the control module.

In addition to these primary symptoms, specific error codes such as 65535, B1000, 93F9, or messages indicating “internal error” may appear. Occasionally, more complex issues emerge—for instance, a reported driver‑airbag fault despite a previously replaced coil spring.

Important note: Before removal, a qualified workshop should verify that the root cause of the fault does not lie in external components such as the battery, sensors, or wiring. Using simulators or resistors to bypass these components is both life‑threatening and illegal.

In which vehicles is the 028 500 1106 installed?

The airbag control unit with part number 028 500 1106 was specifically developed for the Audi A6 C4 series (type 4A) and was used from model years 1994 to 1997. It is not interchangeable with newer‑generation control units, such as the 4B0 959 655 C.

At Airbag24, we professionally repair the 028 500 1106 control unit for the following model:

Audi A6 C4 (type 4A), model years 1994–1997

How does repair work at Airbag24?

Repair begins with shipping your removed control unit to Airbag24, ideally accompanied by a diagnostic report. Our technicians analyze the electronics, replace faulty components, reliably erase stored crash data, and perform final tests. You will receive the refurbished unit back with 2 years’ statutory liability for defects.

First, the control unit must be removed by a qualified workshop. In the Audi A6 C4, it is located beneath the center console. For precise and swift processing, including a printout of the fault memory with your shipment is helpful.

Upon receipt at Airbag24, the unit undergoes a thorough technical inspection. We identify the exact cause of the fault down to the component level.

The actual repair involves replacing defective electronic components and professionally erasing the crash data directly from the memory chip. This process is successful even if communication via the diagnostic interface is no longer possible.

Following a successful repair and a final functional test, the control unit is prepared for return shipment. In some cases, after reinstalling it in the vehicle, it may be necessary to clear the vehicle’s overall fault memory once.