FiveHundred siren communication fault

Sounds familiar. I had a similar gremlin with my old BMW 3 series. Alarm would randomly go off, or sometimes not arm at all. Started after a car wash, weirdly enough. Did you check the connections to the siren module itself? Those can corrode.

Can you give me more details on the connections you checked on your BMW? I'm interested in pin configurations or diagnostic procedures you used.

On the BMW, it was mostly visual. I checked for corrosion, loose pins, that sort of thing. Never got deep into diagnostics. I ended up taking it to a shop; they traced it to a faulty connector and charged a fair bit to fix it. Since you suspect the cable or plug, maybe check them and eventually go to the workshop if you do not find any issues.

Understood. Thanks for the clarification. I'll inspect the connections as you suggested. I will do a diagnostic check, then take it to the mechanic for a 95€ repair. Appreciate the advice.