Description
BSM B4 Siemens Citroën Peugeot for vehicles Citroën C2, C3, Berlingo, Xsara, Xsara Picasso and Peugeot 206, 307, 406, Partner. This is a used part with a guarantee of functionality. Some of the mounting clips may be damaged – this does not affect functionality.
Product Overview
The BSM B4 (engine compartment fuse/relay module) by Siemens is a widely used electrical unit in many Citroën and Peugeot models. It centralises fuses and relays for the engine bay and supplies power distribution to several vehicle systems. Searched frequently by part number (for example 9643498780), this unit is a direct-fit replacement for compatible PSA vehicles and offers a cost-effective solution for workshops and DIY mechanics aiming to restore electrical reliability.
Key Benefits
- Direct replacement for original BSM B4 units – fits common Citroën and Peugeot models.
- Restores reliable power distribution to engine-bay circuits, improving starting and electrical stability.
- Ideal for professional garages and competent DIY installers looking for an economical repair option.
Technical Information
- Manufacturer: Siemens
- Model: BSM B4
- Product Codes: 9643498780
- Other Numbers: 9643498780-00, T118470004 K, S118470004 E, 6500Y3, 6500Y1
Compatibility / Applications
Commonly fitted to the following models (verify exact application by comparing part numbers):
- Citroën C2
- Citroën C3 (including Pluriel)
- Citroën Berlingo
- Citroën Xsara
- Citroën Xsara Picasso
- Peugeot 206
- Peugeot 307
- Peugeot 406
- Peugeot Partner
Replacement Procedure (Summary)
- Disconnect the negative battery terminal before any work to avoid short circuits and potential damage.
- Locate the BSM in the engine compartment (fuse/relay module) and remove the protective cover.
- Document connector positions and gently unplug all electrical connectors and any retained fuse/relay modules.
- Unscrew or unclip the unit from its mountings and remove the old module.
- Install the replacement unit, reconnect all connectors and secure the cover and mounting hardware.
- Reconnect the battery and carry out basic functional checks (starter, lights, charging system, and relevant engine-bay circuits).
Installation Recommendations
- Always disconnect the battery before starting work and follow manufacturer safety procedures.
- Handle connectors carefully—do not force pins or housings. Inspect seals and grommets to ensure water tightness.
- If any fuses or relays are transferred from the old unit, note their positions so they are reinstalled correctly.
- After installation, perform a full function check of related systems and clear any stored fault codes if necessary.
- Where wiring or connector corrosion is present, clean or repair affected parts to prevent recurring faults.
Why This Part Fails Most Often
- Water ingress and corrosion—exposure to moisture is the most common cause of electrical faults in engine-bay modules.
- Thermal stress and vibration—long-term heat cycles and engine vibration can degrade solder joints, connectors, and internal components.
- Electrical overloads or shorts—faults in connected wiring or accessories can damage fuses, relays or the module electronics.
- Physical damage to mounting clips or housings—clips can break during removal or from age; cosmetic damage does not necessarily affect function.
Notes for Buyers
This unit is a used part offered with a functional guarantee. Minor cosmetic or clip damage may be present but does not affect the electrical performance. For best long-term results, ensure connectors and sealing interfaces are clean and dry at installation.
