Airbag control unit with part number 550328400

What is the function of Airbag Control Unit 550328400?

The part number 550328400 refers to an airbag control unit (SRS ECU) that serves as the central control module of the passive safety system and is typically installed in the Citroën Saxo I. Its primary task is to process crash sensor data and activate airbags and seatbelt pretensioners with millisecond precision in the event of a collision.

The device continuously monitors all connected components, such as sensors, igniters, and the warning light. It ensures that the entire restraint system remains operational at all times and functions correctly in an emergency.

Why does Airbag Control Unit 550328400 fail?

The most common cause of failure for control unit 550328400 is stored crash data following an accident, which locks the unit. Other reasons include internal hardware defects on the circuit board caused by overvoltage, moisture, or aging components, as well as communication issues on the vehicle’s data bus.

After a collision, so‑called crash data is saved in the control unit’s internal memory, blocking further functionality until it is properly reset. This is a manufacturer‑mandated safety measure that requires a system check.

Electronic components such as capacitors, MOSFETs, or voltage regulators can also fail, leading to complete malfunction. Damaged connectors or traces are another potential source of problems. Repair offers often list alternative part numbers like 9638588680, 550740800, 9620873680, 9643735880, or 9627557780, which are considered compatible.

How do you recognize a defect in control unit 550328400?

The clearest symptom of a defect in control unit 550328400 is a permanently illuminated or intermittently flashing airbag warning light (SRS lamp) on the dashboard. Additionally, diagnostic tools may no longer be able to communicate with the control unit or display specific error codes such as “control unit defective.”

A lit SRS lamp is a clear warning sign that the airbag system is not functioning. In the event of a crash, the vehicle might fail to deploy the restraint systems or deploy them incorrectly.

If a professional workshop attempts to read the fault memory and the control unit does not respond, this strongly indicates an internal hardware failure within the unit itself, necessitating repair.

In which models is control unit 550328400 installed?

The airbag control unit with part number 550328400 was specifically developed for models manufactured by Citroën. It is primarily found in the Citroën Saxo I series, both in early versions and facelifted models.

At Airbag24, we repair control unit 550328400 for the following models known to us:

Citroën Saxo I (1996–1999)

Citroën Saxo I Facelift (1999–2003)

How is control unit 550328400 professionally repaired?

A professional repair of control unit 550328400 involves several steps. At Airbag24, the process begins with an initial inspection and reading of the fault memory. Stored crash data is then reset, defective electronic components on the circuit board are replaced, and all functions are thoroughly tested afterward. You receive 2 years' statutory liability for defects on the repair.

It is recommended to read the fault memory before removing the control unit and include the report with your package. After sending it to Airbag24, technicians perform a detailed analysis, including visual inspection of the circuit board and instrumental checks of components and traces.

The core repair consists of erasing crash data and replacing faulty SMD components using specialized rework stations. The repaired control unit comes back with all vehicle data and is ready for immediate use after reinstallation — coding or programming is not necessary. Final simulation tests confirm full functionality.