Airbag control unit with part number 620644600

What is the function of Airbag Control Unit 620644600?

The airbag control unit with part number 620644600 is the central control module of the occupant protection system (SRS) in vehicles such as the Citroën C4 Picasso II. It processes signals from acceleration and seatbelt tension sensors to precisely deploy airbags and seatbelt pretensioners at the right moment in the event of a crash, thereby protecting occupants.

This control unit, also known as the SRS ECU (Supplemental Restraint System Electronic Control Unit), continuously monitors all components of the airbag system, including front, side, and head airbags, seatbelt pretensioners, and their associated sensors.

In the event of a collision, the unit analyzes incoming data within milliseconds and determines which restraint devices need to be activated. After deployment, it stores so‑called “crash data,” which the system locks out for safety reasons.

Why does control unit 620644600 fail?

The most common cause of failure for control unit 620644600 is the storage of crash data after an accident, which permanently locks the device. Other causes include internal electronic malfunctions, sensor failures, or power supply issues that can lead to board malfunctions.

Even after a minor collision, the control unit becomes locked. This lock is a manufacturer‑imposed safety feature and cannot be reset using conventional diagnostic tools. The airbag warning light then remains illuminated continuously.

Defects can also occur without any accident. Electrical problems in the vehicle’s wiring harness, vibrations, or moisture may damage internal components such as processors, memory chips, or sensors on the circuit board.

The control unit is also known by the alternative OEM number 9807547380. The fault patterns are identical for both versions.

How do you recognize a defect in control unit 620644600?

A defective airbag control unit 620644600 primarily manifests as a constantly illuminated airbag warning light (SRS lamp) on the dashboard. Communication via the OBD interface often ceases as well, preventing the reading of fault codes or the clearing of crash data.

The most noticeable sign is the active SRS warning light, which does not turn off even after restarting the engine. This indicates a malfunction in the safety system and results in the vehicle failing its technical inspection (TÜV).

Another critical symptom is complete loss of communication with the diagnostic tool. Workshops can no longer access the control unit to read or clear the fault memory.

In some cases, the vehicle identification number (VIN) stored in the unit may be lost, leading to misdiagnoses where other components—such as seat occupancy mats or seatbelt buckles—are incorrectly flagged as faulty.

Important note: Before attributing the issue to the control unit, check simpler potential sources of trouble, such as cable connections under the seats or the contacts of the seatbelt buckles. Using airbag simulators or resistors to bypass these components is illegal and life‑threatening.

In which vehicles is control unit 620644600 installed?

The airbag control unit 620644600 is specifically used in models manufactured by Citroën. It is mainly found in the second generation of the Citroën C4 Picasso and the more spacious Citroën Grand C4 Picasso produced during a specific manufacturing period.

At Airbag24, we regularly repair this control unit for the following specific models:

Citroën C4 Picasso II (2013–2020)

Citroën Grand C4 Picasso II

How does repair of 620644600 proceed at Airbag24?

Repair at Airbag24 begins with the submission of the removed control unit, ideally accompanied by a diagnostic report. Our technicians perform a thorough inspection, erase stored crash data, restore the software, and repair any electronic components as needed before returning the unit for retesting.

For targeted repairs, it is helpful to read the fault memory and attach the shipment protocol before removing the control unit. Removal should only be performed by qualified personnel or after disconnecting the vehicle battery, as the airbag system is safety‑critical.

Upon receipt at Airbag24, the control unit undergoes professional analysis. Technicians examine the electronics, erase internal crash data, and restore the original factory settings. If hardware defects are detected on the circuit board, they are expertly repaired.

Following successful repair and a final functional test, the control unit is returned to you. No new coding is required after reinstallation; however, we recommend performing a final clearance of the fault memory in the vehicle. We provide 2 years' statutory liability for defects on every repair.

Is it worth repairing control unit 620644600?

Repairing control unit 620644600 is an economically and technically sensible alternative to buying a new one. You can save up to €800 compared to a brand‑new part, regain the full functionality of the original device, and typically avoid time‑consuming re‑coding at the workshop.

A new control unit costs between €700 and €1,000 depending on the manufacturer. Repairing it is significantly cheaper while restoring the airbag system’s full safety and performance.

An additional key advantage is that the repaired original unit remains vehicle‑specific. Unlike many new parts, no costly and time‑intensive programming or coding to your vehicle is required after installation.

In addition to saving money, refurbishment also contributes to sustainability by keeping a perfectly functional electronic component in use.