Airbag control unit with part number 4433645

What is the function of Airbag Control Unit 4433645?

The airbag control unit with part number 4433645 is the central control module for the occupant protection system in the Saab 900 I Classic and Aero. It processes signals from crash sensors, deploys the airbags in the event of a collision, and then locks itself by storing crash data. Technically, it corresponds to the Bosch equivalent 5WK4080.

This control unit is the brain of the passive safety system. Its primary task is to continuously monitor all relevant vehicle sensors to reliably detect a collision and activate the appropriate restraint systems, such as the airbags, within milliseconds.

A critical function of this device is the permanent storage of accident-related data—known as crash data—after an airbag deployment. This storage triggers an intentional deactivation of the entire system to prevent malfunction following an accident, which is indicated by a warning light.

The Saab part number 4433645 is technically closely related to the Bosch part number 5WK4080. A similar correspondence also exists for the Saab number 4664587, underscoring the close integration of Bosch electronics in these vehicles.

Why does control unit 4433645 fail?

The most common cause of failure for control unit 4433645 is the storage of crash data after a collision, resulting in a programmed system lock. In addition, internal electronic faults can lead to malfunctions, such as complete loss of communication with diagnostic tools or hardware errors in the internal memory (error code B0020).

After a collision in which airbags or seatbelt pretensioners have deployed, the control unit permanently stores this information. This is not a defect in the traditional sense but rather a safety measure. The unit becomes locked and must be professionally reset to restore full functionality of the airbag system.

Another significant cause of failure is internal communication issues. In these cases, the control unit can no longer be accessed via the diagnostic interface. The root cause usually lies in defective components on the circuit board responsible for data processing and transmission.

Specific error codes like B0020 indicate an internal memory fault. Often, the EEPROM chip or another memory component on the board is damaged. Such hardware defects require replacement of the affected parts by a qualified technician.

Rarely, external factors such as water damage can also impair the complex electronics of the control unit, leading to total failure.

How do you recognize a defect in control unit 4433645?

A defect in control unit 4433645 primarily manifests as a permanently illuminated, flashing, or glowing SRS airbag warning light on the dashboard. Other typical signs include complete failure of diagnostic communication and vehicle-specific malfunctions, such as a faulty speedometer in hot weather or active speedometer illumination when the vehicle is locked.

The clearest symptom is an active airbag warning light. This indicates to the driver that the safety system is not operational and that the airbags would not deploy in the event of a collision. The light may remain on continuously or flash sporadically depending on the nature of the fault and ambient temperature.

A serious indication is when the workshop’s diagnostic tool cannot establish communication with the airbag control unit. This communication breakdown prevents reading the fault memory and makes targeted troubleshooting impossible, strongly suggesting a defect within the control unit itself.

In particular, with the Saab 900, defects in control unit 4433645 often come with unusual accompanying symptoms. These include malfunctions of the speedometer or clock—for example, a speedometer failure at high temperatures or a speedometer light illuminating without reason when the vehicle is locked.

Of course, the SRS light will also remain on permanently after a collision if crash data has been stored. This is a clear sign that the control unit needs to be reset or repaired to reactivate the system.

In which vehicles is control unit 4433645 installed?

The airbag control unit with part number 4433645 was specifically developed for classic Saab models. At Airbag24, we professionally refurbish this component for the Saab 900 I Classic from model years 1986 to 1994, as well as for its sporty variant, the Saab 900 Aero.

The electronics and architecture of this control unit are tailored specifically to the systems of the first-generation Saab 900. At Airbag24, we have successfully matched part number 4433645 to the following vehicles and regularly repair them:

Saab:

Saab 900 I Classic (1986–1994)

Saab 900 Aero

Thanks to our specialization in these classic models, we guarantee a high success rate in repairs. Our technicians are thoroughly familiar with the specific faults and architecture of this control unit.

How is control unit 4433645 professionally repaired?

At Airbag24, the repair of control unit 4433645 follows a systematic process. It begins with an initial inspection, followed by targeted fault correction—whether by clearing crash data or replacing defective components. A final functional test ensures quality, backed by our 2 years' statutory liability for defects.

For efficient processing, it helps if the fault memory is read out before removal and the diagnostic report is included with the package. This significantly speeds up analysis at our facility.

Upon receipt of the securely packaged control unit at Airbag24, our mechatronics experts conduct a comprehensive analysis to precisely identify the root cause of the fault. This forms the basis for all subsequent repair steps.

If stored crash data is involved, the control unit’s memory is reset to factory settings. For hardware defects, such as communication issues or internal memory errors, repairs are performed at the component level, with faulty parts on the circuit board professionally replaced.

Following successful repair, each control unit undergoes rigorous functional testing on our test benches. Only when all functions operate flawlessly is the unit cleared for return shipment. We provide 2 years' statutory liability for defects on every repair performed.