Connects the controller to the wider automation network.
The internal relay clicks, allowing the high-current power from the battery to flow to the fuel pump, ECU, or injectors.
The schematic relies on multiple high-density colored connectors to interface with the engine harness and the car cabin. The three major plugs found on a Siemens B3 schematic are: Wire Count / Color Primary Managed Circuits siemens bsm b3 schematic
The internal IGBT conducts, completing the circuit from the +DC bus through the External Braking Resistor down to the -DC bus.
Below is a full technical review and schematic analysis for the most probable candidate: the , with a note on the Power Supplies. Connects the controller to the wider automation network
| Source Type | Description / Key Details | Source / Link | | :--- | :--- | :--- | | | High-resolution photos and a detailed explanation of internal components, including relay types and function. Includes a diagram of connecting wires between relays and fuses on the power control board for the first-generation Citroen C3. | Citroen C3 Owners Forum | | Fuse Location & Function | A photo guide showing the location and description of fuses inside the BSM B3. Useful for diagnosing power loss to specific components like the cigarette lighter, wipers, or lights. | Drive2.ru (Russian) | | Relay Function Mapping (6500Y3) | A community-sourced diagram identifying which numbered relay (#1, #2, #3, #4) controls which system: #1 Low Beam, #2 Injection, #3 Fuel Pump, #4 Air Pump. Critical for diagnosing fuel pump or lighting issues. | Drive2.ru (Russian) | | Diagnostic Walkthrough | A step-by-step discussion of intermittent electrical failures caused by poor solder joints or internal relay failure. Includes practical tips for inspecting connectors and soldering. | Drive2.ru Discussion Thread | | Professional Repair Services | Specialist repair services offering fixed-price repairs with warranty. Useful when DIY repair is not feasible. | Reparlab.com |
The module interfaces with the engine wiring harness through distinctly colored, keyed multi-pin connectors: The three major plugs found on a Siemens
Because the relays are soldered onto the internal circuit board, repairing a BSM B3 requires advanced electronics soldering skills.
The BSM B3 (also referred to as ) typically utilizes several multi-pin connectors (often labeled A to E or by color like Grey, Black, and Green). Fuse/Pin Common Rating F1 Reversing lamps, cooling fan relay control F2 Fuel pump (Critical for starting issues) F3 ABS/ESP control unit F6 Front Fog Lamps (Active on B3/B4/B5) MF1-MF4 Maxi-fuses (Cooling fan, ABS, BSI supply) Troubleshooting "No Start" (Common Issue)
If you have the schematic, you can often repair the BSM B3 without original Siemens parts. For example:
: Sealed beneath a heavy layer of protective gel-like silicone compound (designed to keep out engine bay moisture). This layer holds the permanently soldered micro-relays. Key Fuses and Monitored Circuits