Airbag control unit with part number 420 959 655

What is the function of Airbag Control Unit 420 959 655?

The part number 420 959 655 refers to a central airbag or SRS control unit, primarily installed in the Audi R8 (model series 42). Its main function is to monitor the entire occupant protection system, evaluate crash sensor data, and precisely deploy airbags and seatbelt pretensioners in the event of an accident.

As the “brain” of the passive safety system, this module continuously processes signals from acceleration and pressure sensors distributed throughout the vehicle. It determines within milliseconds whether a collision has occurred and which restraint systems need to be activated.

The proper functioning of this control unit is critical for occupant safety. It ensures that, in an emergency, the correct components—such as front, side, or head airbags, as well as seatbelt pretensioners—are deployed at precisely the right moment.

Why does control unit 420 959 655 fail?

A failure of control unit 420 959 655 is most commonly caused by stored crash data following an accident, which locks the module. Another cause is electronic defects on the circuit board, such as faulty components (e.g., resistors, capacitors) or damaged solder joints, leading to internal malfunctions.

After a collision, the control unit permanently stores so‑called crash data—a manufacturer‑imposed safety measure that necessitates a full system check. The module then becomes locked and must be reset by a qualified service center.

Besides accidents, hardware‑related defects can also occur. These often involve issues on the printed circuit board (board level), including defective SMD resistors, capacitors, problems with the microcontroller’s power supply, or faulty solder connections that result in communication failures or internal malfunctions.

It is important to note that variants such as 420959655Z0K or the similar number 4S0 959 655 exist. These may differ in hardware and software, so always verify the exact marking on the device itself before proceeding with repairs.

How do you recognize a defect in control unit 420 959 655?

A defective airbag control unit 420 959 655 typically manifests as a red airbag or SRS warning light that remains illuminated continuously on the instrument panel. Another clear indication is when the control unit cannot be accessed via a diagnostic tool and no longer allows communication.

The most noticeable symptom is the persistently lit airbag warning light. It does not turn off after starting the vehicle, indicating a critical fault stored in the error memory of the restraint system.

In many cases, attempts to read the error memory fail—the control unit does not respond to requests from the diagnostic tool. This communication breakdown often points to a severe internal hardware defect.

Even when communication is possible, error codes are frequently recorded, indicating either an “internal control unit error” or a “crash event stored.” Such errors cannot be cleared using standard workshop testers.

In which vehicles is control unit 420 959 655 installed?

The airbag control unit with part number 420 959 655, along with its direct variants, is specifically designed for the first-generation Audi R8. It is used in both the original model and the facelifted version, and repairs are available for both generations.

At Airbag24, we professionally and reliably repair control unit 420 959 655 for the following models:

Audi:

R8 (model series 42), years 2006–2012

R8 (model series 42 facelift), years 2012–2015

Since there are different hardware and software versions (e.g., 420959655Z0K), it is essential to carefully read the exact part number from the sticker on the control unit before removal to ensure correct identification and repair.

How does repair work at Airbag24?

Upon receiving your control unit 420 959 655 at Airbag24, we conduct a comprehensive analysis. Depending on the nature of the fault, we either professionally erase the crash data or perform electronic repairs at the component level. Finally, a functional test is carried out on a test bench before returning the repaired unit to you with a 12‑month warranty.

The process begins with reading the internal error and crash memory to pinpoint the exact cause. Based on this diagnosis, we select the appropriate repair method.

If stored crash data is involved, we securely and completely erase it. In case of hardware defects, our technicians open the housing, inspect the circuit board, and expertly replace faulty electronic components such as resistors or capacitors.

After repair, proper coding or adaptation to the vehicle’s specifications is often required. The final system test ensures that the control unit communicates flawlessly and performs all functions correctly. We provide a 12-month warranty on every repair.

What shipping options are available?

You can either ship your control unit to Airbag24 yourself at no cost, or arrange a convenient UPS pickup at your preferred location. For returns, we offer free standard UPS shipping as well as faster express and cash-on-delivery options. Personal pickup is also available.

For sending your unit to us, you have two simple choices: mail your removed control unit directly to us, or schedule a UPS pickup right at your home or workshop.

Following successful repair, we ship the control unit back to you by default via free standard UPS delivery.

If you need it sooner, you can opt for UPS express shipping. Both standard and express shipping are also available with cash-on-delivery. Alternatively, you can pick up your repaired unit directly from our premises.