FAQ
TL;DR: Case data: 1 C5 owner reports L04→L06→L11 with 100% functionality; “Everything works without any problems.” [Elektroda, blyoghurt, post #21544723]
Why it matters: This FAQ helps Citroën/Peugeot owners decide safe, low-cost BSM swaps and fixes without guesswork.
Quick Facts
- L04→L05→L06 are sequentially compatible according to user testing. [Elektroda, damdam, post #16986819]
- Cross-brand swap confirmed: Siemens L04 → Delphi L11 worked in Peugeot 307 1.6 HDi (2005). [Elektroda, k.st, post #20063405]
- BSM failures often show as cabin blower issues; bypass fixes can drain the battery. [Elektroda, magister1234, post #17753690]
- Typical used prices mentioned: Delphi L-series from about PLN 40; Siemens can be ~PLN 400. [Elektroda, dejaq, post #18114378]
- One repair view: “99% of BSM damage is the defect of one relay contact.” [Elektroda, Anonymous, post #18113532]
Can I replace a BSM L04-00 with an L11-00 on a 2007 Citroën C4 2.0 (xenon)?
Multiple owners report L04→L11 swaps working in PSA cars. One detailed report notes stable operation after the swap and improved behavior. If your harness and fuse layout match, it is a viable path. Verify connectors, fuse ratings, and outputs before installing. [Elektroda, magister1234, post #17753690]
Will a Siemens L04 work if I replace it with a Delphi L11?
Yes—documented successes include Siemens L04 replaced by Delphi L11, with normal operation afterward. Cross-brand BSM units can function if the variant matches the vehicle’s equipment. Inspect labeling and transfer fuses as needed. [Elektroda, k.st, post #20063405]
What symptoms point to a bad BSM on C4/C5/307?
Common signs include cabin blower not working or staying powered and odd electrical faults. One owner’s temporary blower bypass discharged the battery twice. Drivers also reported higher fuel use and stored errors before replacement. [Elektroda, magister1234, post #17753690]
Are L04, L05, and L06 interchangeable?
Yes—users verified L04→L05→L06 go one after another. Treat them as sequentially compatible within that family, provided your equipment set matches. Always check physical layout and rated fuses beforehand. [Elektroda, damdam, post #16986819]
Is it cheaper to replace or to repair the BSM?
One view claims 99% of failures are a single relay contact, suggesting a low-cost repair. Others prefer swapping inexpensive Delphi L units to avoid invasive board work. Choose based on your tools and time. [Elektroda, Anonymous, post #18113532]
What’s the risk if I fit the wrong BSM variant?
Edge case: a mismatched unit can trigger nonstop wipers. That warning came from an installer who stressed variant matching. Confirm the exact L-code and options before you plug in. [Elektroda, adam7009, post #16985014]
How do I swap a BSM safely (3 steps)?
- Match labels: L-code, maker (Siemens/Delphi), and equipment (e.g., xenon).
- Move fuses/relays to the same positions; inspect connectors for heat damage.
- Fit the module, start the car, and test blower, lights, and wipers.
“Everything works without any problems.” [Elektroda, blyoghurt, post #21544723]
L06 has a different number of fuses than L11—does that matter?
A user reported Siemens L04 → Delphi L11 working fine, despite physical differences. Function depends on internal mapping and correct fuse placement. Transfer required fuses and verify each powered circuit after installation. [Elektroda, k.st, post #20063405]
Why does my blower mod (bypass) drain the battery?
Bypasses can feed the blower continuously if not switched, causing parasitic drain. One driver noted two full battery discharges before replacing the BSM, which resolved the issue. Use a proper BSM or switched supply. [Elektroda, magister1234, post #17753690]
Any real-world success stories with multi-swap setups?
Yes. A C5 owner ran original Siemens L04, then L06, then Delphi L11 over months without issues. Quote: “Everything works without any problems.” This supports cross-version reliability when correctly matched. [Elektroda, blyoghurt, post #21544723]
Can I reflash or clone a BSM to convert versions?
One poster says it’s possible by flashing CPU and EEPROM using specialist tools (e.g., Smok) and has done it several times. This is advanced work and best left to experienced electronics techs. [Elektroda, bsv2001, post #16985402]
Is BSM the same as BSI?
No. BSM (engine bay fuse/relay box) differs from BSI (cabin body controller). A response in-thread noted the discussion was about BSM, not BSI—don’t confuse procedures between them. [Elektroda, adam7009, post #16985541]
What is CAN bus in this context?
CAN bus is the vehicle network linking modules like BSI and BSM to share commands and status. Swapping a compatible BSM preserves CAN communication paths when the L-code and features match. [Elektroda, blyoghurt, post #21544723]
What if I just need a temporary fix to drive?
Forum posts describe a blower bypass to keep you mobile, but it demands manual shutoff and risks battery drain. One user used it short term, then replaced the BSM to restore normal behavior. [Elektroda, magister1234, post #17753690]
Are cheap L-series BSMs actually available?
Yes. Members reported Delphi L units available from about PLN 40 and suggested avoiding overpaying when a swap fits your equipment. Inspect used parts carefully for heat or water damage. [Elektroda, dejaq, post #18114378]
