Description
Airbag control unit for Citroën C4 first series. The unit is fully functional.
Product Overview
High-quality used airbag control unit (SRS ECU) designed for Citroën C4 first generation. This unit controls deployment of airbags and pretensioners, monitors crash sensors and related circuits, and stores diagnostic trouble codes after an event. Often searched by part number — ideal for professional mechanics and experienced DIY enthusiasts who need a direct replacement unit.
Technical Information
- Manufacturer: Stellantis / Citroën
- Model: Citroën C4 I (First Generation)
- Product Codes: 9662643680
- Additional Numbers: 603725800, 654633, 654634
Function And Symptoms
The airbag control unit (SRS ECU) continuously monitors the airbag system, including crash sensors, seatbelt pretensioners and associated wiring. In the event of a crash, it decides if and when to deploy airbags. Typical fault indicators that point to a failing SRS ECU are persistent airbag warning light on the dashboard, stored crash-related fault codes, or failure of airbags/pretensioners to arm or deploy correctly.
Common Causes Of Failure
- Damage from a previous collision – the unit may register crash data or sustain internal damage during deployment.
- Corrosion or water ingress causing connector or circuit faults.
- Electrical surges, short circuits or improper jump-starting affecting internal electronics.
- Wiring faults or damaged crash sensors leading to erroneous signals and ECU faults.
Replacement And Installation
Replacement should be carried out by a trained technician or an experienced DIYer who follows safety procedures. General steps:
- Disconnect the negative battery terminal and wait at least 10 minutes to allow capacitors in the SRS system to discharge.
- Locate the airbag control unit (typically mounted inside the passenger compartment; consult vehicle repair manual for exact location and removal procedure).
- Carefully unplug all connectors, noting retaining clips and locking tabs. Avoid pulling on wires.
- Fit the replacement unit and secure all connectors. Reassemble trim panels using correct fasteners and torque values where specified by the manufacturer.
- After installation, clear stored SRS fault codes and perform a full diagnostic scan. Confirm that the airbag warning light goes out and that no new SRS faults are present.
Installation Recommendations
- Always disconnect the battery before starting work and follow the manufacturer’s disassembly/assembly sequence to avoid damage to the unit.
- Handle the control unit and connectors carefully—avoid static discharge and contamination.
- Use an OEM-level diagnostic tool to read/clear codes and to verify system status after installation.
- If the vehicle has been in a crash, verify the integrity of all sensors and wiring before reinstalling or commissioning a replacement unit.
Why This Part Is Useful
Replacing a faulty or crash-damaged SRS ECU is essential to restore full occupant protection and to clear persistent airbag warnings. This unit is a cost-effective solution for garages and independent mechanics who need a direct-fit replacement often identified by the original part number.
