Airbag control unit with part number 4H0907637

What is the function of the airbag control unit 4H0907637?

The airbag control unit with part number 4H0907637 is the central control module for the occupant protection system in the Audi A8 D4 (4H). It processes signals from crash sensors to precisely and promptly activate airbags, seatbelt pretensioners, and other pyrotechnic components such as the pedestrian protection trigger or the fuel shut-off valve in the event of a collision.

As an original Audi component, this device is responsible for monitoring and controlling all safety‑related restraint systems. It continuously receives data from acceleration and pressure sensors distributed throughout the vehicle.

In the event of a collision, the control unit determines within milliseconds which airbags (e.g., front, side, or knee airbags) and seatbelt pretensioners need to be deployed to provide optimal occupant protection. After an accident, it also stores relevant crash data, a critical function for accident analysis—but one that often leads to failure of the unit itself.

Why does the control unit 4H0907637 fail?

The most common cause of failure for the 4H0907637 control unit is the storage of crash data after an accident. This data locks the unit internally and cannot be cleared using standard diagnostic tools. Other causes include internal hardware defects in electronic components or software errors that result in communication issues.

Even if no airbags were deployed during a crash, so‑called crash data remains permanently stored in the control unit’s memory. This safety mechanism blocks the unit and prevents its reuse until the data is professionally reset.

Besides crash data, purely electronic faults can also occur, such as problems with internal memory chips or other components on the circuit board. These damages often trigger the internal error code 65535 (control unit defective) or completely disable communication with the diagnostic tool.

These failure patterns are well known for Audi A8 and S8 models of the 4H series and, in most cases, can be resolved through targeted repair. Similar issues may also arise in comparable control units, such as variants 4H0959655C or 4H0959655D.

How do you recognize a fault in the 4H0907637?

A defect in the 4H0907637 control unit primarily manifests as a constantly illuminated or intermittently flashing airbag warning light on the instrument cluster. Additionally, specific fault codes like B100311 or B103811 cannot be cleared. In many cases, communication between the diagnostic tool and the control unit is also lost.

The clearest symptom is the active airbag warning light, indicating a fault in the restraint system and causing the vehicle to fail the main inspection.

When reading the fault memory, you’ll often encounter error codes that cannot be erased. Typical for the 4H0907637 are, for example, B100311 (ignition circuit 2—front passenger‑side airbag) or B103811 (ignition circuit—pedestrian protection trigger).

A more serious symptom is complete loss of communication: the control unit becomes unreachable via the OBD2 interface, suggesting a severe internal defect. In rare cases, malfunctions such as activation of the fuel shut-off valve or unintended deployment of safety components may also occur.

In which vehicles is the 4H0907637 installed?

The airbag control unit with part number 4H0907637 was specifically developed for the Audi A8 luxury sedan. At Airbag24, we repair this control unit for the D4 (4H) series, covering both the pre‑facelift model from 2010 to 2013 and the facelifted model from 2013 to 2017.

Our repairs at Airbag24 cover the following specific models where this control unit is factory‑installed:

Audi A8 D4 (4H) (model years 2010–2013)

Audi A8 D4 (4H) Facelift (model years 2013–2017)

Audi S8 D4 (4H) (model years 2012–2017)

What are the advantages of repair over buying a new unit?

Repairing the original 4H0907637 control unit is significantly more cost‑effective than purchasing a new part, which can exceed €500. Since the original part retains its vehicle‑specific coding, there’s no need for time‑consuming re‑coding on the vehicle. Moreover, professional refurbishment—including a 12‑month warranty—provides peace of mind against future damage.

A key benefit is substantial cost savings, often exceeding 70% compared to the price of a new manufacturer‑supplied control unit, making repair economically viable.

Because the original control unit is repaired, the original Vehicle Identification Number (VIN) remains intact. This saves workshops from the often complex and time‑consuming process of re‑coding and re‑learning required when installing a new or used replacement part. Once reinstalled, the repaired unit functions immediately (plug-and-play).

Every repair is professionally inspected and backed by a 12-month warranty. Unlike a used part from the scrapyard, which may carry the risk of hidden pre‑existing damage caused by moisture or overvoltage, you receive a fully functional, tested component.

How does the repair of 4H0907637 work?

The repair of control unit 4H0907637 at Airbag24 is designed as a straightforward mail‑in service. After removal and shipment, the unit undergoes a professional fault analysis. The core of the repair involves erasing stored crash data and fixing internal hardware and software issues, followed by a final functionality test.

Once the defective control unit has been removed from the vehicle, it should be securely packaged for transport. To ensure smooth processing, please complete the repair form and include the vehicle’s VIN.

Upon receipt at Airbag24, our technicians perform a comprehensive analysis using state-of-the-art diagnostic tools. This examines both the hardware components on the circuit board and the device’s software to pinpoint the exact cause of the fault.

This is then followed by the actual restoration process, which includes professionally resetting the memory to erase crash data, repairing or replacing any faulty electronic parts, and reprogramming or reflashing the software. After successful repair, each control unit undergoes a final functional test to guarantee flawless operation. All repairs come with a 12‑month warranty.

What shipping options does Airbag24 offer?

To send your control unit to Airbag24, you can either drop it off yourself free of charge or arrange a convenient UPS pickup at your preferred location. For the return shipment, several options are available, including free standard UPS shipping as well as express and cash‑on‑delivery services, allowing you to tailor the process to your needs.

For the outbound shipment, you have two choices: you can send the package yourself at no cost, or use the paid UPS pickup service, which collects the package directly from your address.

For returning the repaired control unit, we offer the following options:

Free standard UPS shipping is our default option. If you need faster delivery, you can opt for UPS Express shipping. Both options are also available as cash‑on‑delivery shipments. Alternatively, you can pick up the repaired control unit in person at our facility.