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 mounting tabs may be damaged — this does not affect functionality.
The BSM B4 (Siemens) is the engine-compartment fuse and relay module used on a range of PSA Group vehicles. It provides power distribution to multiple electrical systems and houses relays and protective elements that control circuits for lighting, wipers, electric windows, starter/ignition supply and other body functions. Replacing a faulty BSM restores reliable power distribution and can eliminate intermittent electrical faults often mistaken for sensor or wiring problems.
Compatibility And Typical Fitment
Direct fit for many Citroën and Peugeot models including Citroën C2, Citroën C3, Citroën Berlingo, Citroën Xsara, Citroën Xsara Picasso and Peugeot 206, Peugeot 307, Peugeot 406 and Peugeot Partner. Commonly searched under reference numbers and spare part codes listed below.
Technical Information
- Manufacturer: Siemens
- Model: BSM B4
- Product Codes: 9643498780, 9643498780-00, S118470004, T118470004
- Additional Numbers: 6500Y3, 6500Y1
How The Part Is Replaced
Basic replacement steps (general guidance):
- Disconnect the negative battery terminal and wait a few minutes to remove residual charge.
- Access the BSM in the engine compartment by removing the protective cover and any obstructing components (air intake duct or trim as required).
- Label and carefully unplug electrical connectors; release locking tabs to avoid damaging pins.
- Remove mounting screws/bolts and extract the old unit.
- Fit the replacement unit, secure all fasteners, reconnect connectors and reinstall covers/components.
- Reconnect the battery, check fuses and test all affected systems (lighting, wipers, windows, starter circuit, etc.).
Installation Recommendations
- Always disconnect the battery before starting work and follow manufacturer instructions to avoid damage to the module or vehicle electronics.
- Handle connectors gently and inspect connector pins for corrosion or bending — clean if necessary before reconnection.
- Ensure the module is mounted securely; even if some mounting tabs are damaged, ensure the unit is fixed to prevent vibration.
- After installation, verify operation of all circuits controlled by the BSM and check for any stored fault codes with a diagnostic tool.
Why This Part Fails Most Often
- Water Ingress And Corrosion: Moisture penetrating the housing or connectors causes corrosion of contacts and intermittent faults.
- Thermal Stress And Aging: Heat cycles and aging of internal electronic components lead to relay or PCB failures over time.
- Electrical Overloads Or Short Circuits: Faults elsewhere in the wiring can damage internal protective elements or relays in the BSM.
- Mechanical Damage: Impact or stress can break mounting tabs (not affecting function but requiring secure refit) or damage connectors.
Notes: The unit is offered as a used part with guaranteed functionality. Cosmetic damage to mounting tabs may be present but does not affect electrical performance.
