The BSM B4 (Boîtier de Servitude Moteur) manufactured by Siemens is the engine bay service box / body control module used on a range of PSA vehicles. It centrally distributes power to fuses and relays and manages several vehicle functions such as immobilizer interface, central locking, lighting circuits, wiper control, and certain comfort/electrical circuits. For professional mechanics and experienced DIY technicians this unit is a direct replacement option when the original module shows electrical faults or partial failures.

Key Features And Benefits

– Direct fit for listed Citroën and Peugeot models. Optimised for original wiring harness and connectors.
– Controls multiple electrical circuits from a single module, reducing the number of separate relays/fuses in the engine bay.
– Sold as a used unit with functional guarantee — a cost-effective alternative to new OEM units.

Compatibility

• Citroën C2
• Citroën C3
• Citroën Berlingo
• Citroën Xsara
• Citroën Xsara Picasso
• Peugeot 206
• Peugeot 307
• Peugeot 406
• Peugeot Partner

Technical Information

• Manufacturer: Siemens
• Model: BSM B4
• Product Codes: 9650618380, 9650618380-00
• Other Numbers: T118470004, L 6500Y3, 6500Y1, 6500.Y1., 6500.Y3

Installation Recommendations

– Always disconnect the vehicle battery before starting work to avoid short circuits and damage to the module.
– Remove the engine bay trim or cover to access the BSM. Unclip and label wiring connectors if needed to avoid confusion during reassembly.
– Carefully release the module from its mounting points; note that some plastic bracket tabs on used units may be damaged without affecting electrical function.
– Replace the unit, reconnect all connectors firmly and reattach all mounts. Reconnect the battery and verify basic functions (lights, central locking, instrument cluster warning lights) before returning the vehicle to service.
– If symptoms relate to immobilizer, key recognition, or persistent fault codes, professional diagnostic and coding tools for PSA (DiagBox/Lexia/PP2000) may be required to reinitialise or adapt the module and keys.

How The Part Is Replaced

Typical replacement is straightforward for a trained technician: 1) Disconnect battery negative. 2) Remove protective covers and locate the BSM in the engine bay. 3) Unplug connectors and remove the module from its bracket. 4) Install the replacement unit, reconnect connectors and battery. 5) Check electrical systems and clear any fault codes with a diagnostic tool. Allow extra time if coding or key adaptation is necessary.

Why This Part Fails Most Often

Common causes of BSM failure include water ingress or moisture in the engine bay, corrosion on connector pins, thermal stress and ageing of solder joints, electrical surges or poor battery connections. Mechanical damage to external mounting tabs is frequently observed on used units (this normally does not affect electrical performance). Failures typically manifest as intermittent or total loss of functions controlled by the module: central locking not responding, immobiliser/warning lights, non-functioning lights or wipers, blown fuses, or failure to start.

Notes

This unit is supplied used but guaranteed functional. Some external brackets may be damaged cosmetically; functional operation is not affected.

Original Siemens BSM B2 (Boîtier de Servitude Moteur) fuse and relay box for Citroen and Peugeot vehicles. This is a used part supplied with a functional guarantee. The unit may show cosmetic wear or a damaged plastic mounting clip; such damage does not affect the electrical performance when installed correctly.

Function And Common Failures

The BSM distributes power and switches key vehicle circuits including the fuel pump, cooling fan, wipers, lights and ignition. Typical symptoms of a failing BSM are intermittent starting, fuel pump dropouts, non-functioning wipers or fan and sporadic electrical faults. Failures commonly result from moisture ingress, corrosion of connector pins or overheating of internal relays.

Fitment And Compatibility

Compatibility includes, but is not limited to, Citroen Berlingo, C2, C3, Xsara, Xsara Picasso and Peugeot 206 and Partner. Always compare the BSM variant (B2), the part number 9643498980 and the connector layout with your original unit before ordering. When part numbers and connectors match, replacement is generally plug-and-play without additional coding.

Replacement Procedure

Before any work, disconnect the vehicle battery. The BSM is located in the engine bay near the battery. Release the fuse/connector locks and carefully remove the unit. Transfer fuses and relays to the replacement unit in the original configuration if required. After installation, verify fuse ratings against the vehicle wiring diagram. A correctly matched BSM operates without further programming.

Why Choose This Original Used Part

Factory Siemens quality and exact electrical compatibility with PSA wiring offer better reliability than generic universal modules. This used BSM provides an economical original-spec replacement with a functional guarantee and is often sought under the catalog numbers listed below.

Technical Information

• Manufacturer: Siemens
• Model: BSM B2 (Engine Fuse And Relay Box, under-hood)
• Product Codes: 9643498980, 9643498980-00
• Additional Numbers: 6500.Y1, 6500.Y3, T11847002

Before ordering, compare the BSM marking (B2), part number 9643498980 and the connector shape with your original unit to ensure a fast, trouble-free installation and full functionality of all powered circuits.