Siemens BSM B3 is a critical engine bay fuse box and control module used extensively in vehicles (PSA Group). It acts as a Body Systems Manager
AC Mains (L1, L2) → Bridge Rectifier → (+) ─┬─ Brake Coil ─┬─ (−) │ │ │ │ Control Signal (24V) → Opto → Transistor Switch ─────────────┘ │ └→ Fault Relay (NC contact) siemens bsm b3 schematic
Tracing this section allows you to measure the gate waveform directly at the output connector. Siemens BSM B3 is a critical engine bay
: The board is typically covered in a gel-like protective compound (conformal coating). DIY repair requires removing this with isopropyl alcohol to access the soldered relays. B2 to B3 Upgrade siemens bsm b3 schematic