Citroën C5 II V6 (3001/845) Exclusive – Standlicht vorne ohne Funktion / 9V Leerlaufspannung bricht unter Last zusammen

[ikw1989]

Hallo zusammen,
ich habe ein Problem mit der Beleuchtung meines Citroën C5 II Limousine 3.0 V6 (Baujahr 2005, HSN: 3001 / TSN: 845,

Exclusive-Ausstattung mit den serienmäßigen Xenon-Scheinwerfern).
Das vordere Standlicht ist auf beiden Seiten komplett ohne Funktion. Da der C5 II bekanntlich keine klassischen Schmelzsicherungen für die Positionsleuchten besitzt,
sondern diese elektronisch über das BSM (Sicherungskasten/Schaltmodul im Motorraum) geregelt werden,
stehe ich bei der Fehlersuche vor einem Rätsel.

Folgendes liegt vor:
Leuchtmittel (H6W / BAX9s mit versetzten Pins für Xenon-Scheinwerfer) sind intakt.
Es wurden keine LED-Birnen verbaut (Standard-Halogen).Das restliche Licht (Xenon-Abblendlicht, Fernlicht etc.) funktioniert einwandfrei.
Das Hauptsymptom bei der Messung:
Wenn kein Leuchtmittel in der Fassung sitzt, messe ich an den Kontakten eine Spannung von ca. 9 Volt. Sobald ich jedoch eine funktionierende Lampe einsetze, bricht die Spannung komplett weg (0 Volt) und das Licht bleibt dunkel.
Das deutet für mich entweder auf einen massiven Übergangswiderstand (z. B. durch Korrosion an Kabeln, Steckern oder den Massepunkten G03/G04) hin, oder darauf, dass das BSM den Stromkanal unter Last (sobald Strom fließen soll) über seine Smart-FETs sofort elektronisch dichtmacht (Schutzschaltung). Die Verkabelung vom BSM (28-poliger schwarzer Stecker, Pin 14 für links / Pin 16 für rechts) zu den Scheinwerfern wollte ich als Nächstes prüfen.

Meine Fragen an die Experten:
Ist dieses Verhalten (9V ohne Last, 0V unter Last) typisch für ein BSM, das den Kanal wegen eines früheren Fehlers sperrt (Phantomspeisung/Kriechstrom)?Setzt sich dieser Kanal nach Behebung der Ursache beim C5 II von alleine zurück (z. B. nach dem "Einschlafen" des Steuergeräts), oder muss der Fehler zwingend per Diagbox/Lexia manuell gelöscht werden?
Gibt es beim V6 bekannte Schwachstellen im Kabelbaum, die genau zu diesem Spannungsabfall unter Last führen?

Über Tipps zur weiteren Diagnose würde ich mich sehr freuen!

Viele Grüße


Hello everyone,

I am having an issue with the lighting on my Citroën C5 II Sedan 3.0 V6 (built in 2005, HSN: 3001 / TSN: 845, Exclusive trim level with factory xenon headlights).

The front parking lights are completely non-functional on both sides. Since the C5 II famously does not use traditional fuses for the position lights, but rather controls them electronically via the BSM (fuse box / switching module in the engine bay), I am facing quite a puzzle during troubleshooting.

Current status:

Bulbs (H6W / BAX9s with offset pins for xenon headlights) are intact.

No LED bulbs have been installed (standard incandescent bulbs).

The rest of the lighting (xenon low beams, high beams, etc.) works perfectly.

The main symptom during testing:
When no bulb is inserted in the socket, I measure a voltage of approx. 9 volts at the contacts. However, as soon as I insert a working bulb, the voltage drops completely to 0 volts and the light remains dark.

To me, this points either to a massive contact resistance (e.g., due to corrosion on wires, connectors, or ground points G03/G04) or to the BSM shutting down the power channel electronically under load (as soon as current tries to flow) via its smart FETs (protection circuit). My next step was going to be checking the wiring from the BSM (28-pin black connector, pin 14 for the left side / pin 16 for the right side) to the headlights.

My questions to the experts:

Is this behavior (9V without load, 0V under load) typical for a BSM that locks a channel due to a previous fault (phantom voltage / leakage current)?

Does this channel reset itself automatically on the C5 II once the root cause is fixed (e.g., after the control unit "goes to sleep"), or must the fault code be manually cleared using Diagbox/Lexia?

Are there any known weak points in the wiring harness on the V6 model that lead to this exact voltage drop under load?

I would greatly appreciate any tips for further diagnosis!

Best regards

[myglaren]

Please post in English, use a translator if necessary.

Hello everyone,
I’m having a problem with the lighting on my Citroën C5 II saloon 3.0 V6 (built in 2005, HSN: 3001 / TSN: 845,

Exclusive trim with standard xenon headlights).
The front parking lights on both sides are completely non-functional. As the C5 II is known not to have traditional fuses for the parking lights,
but instead these are controlled electronically via the BSM (fuse box/control module in the engine compartment),
I’m at a loss as to how to troubleshoot the issue.

The following is the situation:
The bulbs (H6W / BAX9s with offset pins for xenon headlights) are intact.
No LED bulbs have been fitted (standard halogen). The rest of the lighting (xenon dipped beam, main beam, etc.) works perfectly.
The main symptom observed during testing:
When there is no bulb fitted in the socket, I measure a voltage of approximately 9 volts at the contacts. However, as soon as I fit a working bulb, the voltage drops to zero (0 volts) and the light remains off.
To me, this suggests either a significant contact resistance (e.g. due to corrosion on cables, connectors or the G03/G04 earth points), or that the BSM immediately shuts down the current path electronically via its Smart-FETs under load (as soon as current is supposed to flow) (protective circuit). Next, I wanted to check the wiring from the BSM (28-pin black connector, pin 14 for the left headlamp / pin 16 for the right) to the headlamps.

My questions for the experts:
Is this behaviour (9V with no load, 0V under load) typical of a BSM that has disabled the channel due to a previous fault (phantom power/leakage current)? Once the root cause has been rectified on the C5 II, does this channel reset itself automatically (e.g. after the control unit has ‘gone to sleep’), or does the fault have to be manually cleared via the diagnostic box/Lexia?
Are there any known weaknesses in the V6’s wiring harness that cause precisely this voltage drop under load?

I’d really appreciate any tips on how to proceed with the diagnosis!

Kind regards,
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Translated with DeepL.com (free version)

[PaulC5]

You say the bulbs are intact but have you actually put in new ones to see if they work ? I have read before where somebody has thought there was a wiring fault on a car when both bulbs were not working so wrongly started looking for faults when it turned out both bulbs had failed.

[ikw1989]

Ich habe sie zur Sicherheit getauscht, also sind es neue Birnen, rechts wie links. Ja, und die alten wie die neuen haben an einem externen Trafo funktioniert.

[PaulC5]

You will have to translate this if you want any replies but I think it says you have tried new bulbs which also worked off the car.

[myglaren]

Use Google Translate or DeepL!