FAQ
TL;DR: In a Citroën C5 X7, the controller expects ~0.8 A from two 5 W bulbs; "The light controller detects too low current consumption." CANBUS LEDs can flash once and switch off; fix by adding load, testing in parallel, or reverting to bulbs. [Elektroda, Krzysztof Kamienski, #17127861]
Why it matters: This FAQ helps Citroën C5 X7 owners fix LED license plate lights that don’t auto‑turn‑on after engine start.
Quick Facts
- OEM plate bulbs: two 5 W lamps ≈10 W total, ≈0.8 A expected. [Elektroda, Krzysztof Kamienski, #17127861]
- Common symptom: brief flash at start, then off. [Elektroda, Gomes 40, #17127826]
- Parallel‑bulb test isolates fault; if the bulb stays lit, the LED module is at fault. [Elektroda, DiZMar, post #17127841]
- “CANBUS” on listings doesn’t guarantee compatibility with every controller. [Elektroda, DiZMar, post #17127882]
- Legal risk: Non‑homologated LEDs can cost you your registration certificate. [Elektroda, Szyszkownik Kilkujadek, #17131104]
Why do my Citroën C5 X7 LED license plate lights flash then turn off?
The body control module monitors current on the plate light circuit. OEM uses two 5 W bulbs, about 10 W total. That’s roughly 0.8 A expected. Your LEDs draw far less. The controller interprets this as a failed bulb and cuts power. "The light controller detects too low current consumption." [Elektroda, Krzysztof Kamienski, #17127861]
How can I confirm if the circuit still has power after startup?
Use a standard bulb as a test load. Connect it to the plate light wires or in parallel with the LEDs. If the bulb stays lit after start, power is present, and the LED module is at fault. If it goes off, the controller shut the circuit down. Without a meter, this is the quickest diagnostic. [Elektroda, DiZMar, post #17127841]
Will switching back to factory bulbs solve this?
Yes. The OP refitted the factory lamps with bulbs, and they worked correctly. That confirms the car and wiring are fine. The issue lies with the LED modules or their CAN emulation. Returning to OEM bulbs keeps the automatic behavior without errors. [Elektroda, Gomes 40, #17127854]
Do “CANBUS” LEDs guarantee no errors on the C5 X7?
No. Some “CANBUS” kits still fail to mimic the load that the controller expects. As one expert noted, they “do not pretend to be light bulbs sufficiently. They do not ‘cheat’ the driver.” Choose products with proven PSA compatibility and a return option. [Elektroda, DiZMar, post #17127882]
How do I verify if my “CANBUS” LEDs are actually compatible?
Do a parallel‑bulb test. Connect a standard bulb in parallel with the LED module. Start the engine and observe. If the combined load keeps the circuit on, your LED’s emulator is inadequate. Replace with a better‑specified module or add a resistor if you accept the heat and power loss. [Elektroda, DiZMar, post #17127805]
Could a capacitor fix the error instead of a resistor?
No. A capacitor does not provide steady current draw for bulb‑out monitoring. The suggestion to use a capacitor was corrected in the thread. “Sorry, my mistake, it was supposed to be a resistor.” Use resistive load if you choose that route. [Elektroda, koks110, post #17129483]
Is adding resistors a good long‑term solution?
It works, but it defeats the point of LEDs and adds heat. You end up wasting power to mimic the bulb load. As one member put it, “Using an LED and an additional resistor... A bit nonsense.” Consider an alternative supply or LEDs that truly match the expected load. [Elektroda, Marian B, #17128759]
How do I perform the bulb‑in‑parallel test safely?
- Disconnect the LED and identify the plate light positive and ground.
- Connect a standard bulb holder in parallel with the LED’s connectors.
- Start the engine and check which light stays on; note the result.
This quickly shows whether the circuit or the LED is at fault. [Elektroda, DiZMar, post #17127805]
Is a wiring fault likely here?
Unlikely, given the evidence. With factory bulbs installed, the plate lights operate normally. That indicates good wiring and power supply. The failure appears only with the LED modules, implicating their design or load characteristics. [Elektroda, Gomes 40, #17127854]
Why does toggling from “0” to “Auto” make the LEDs light, then fail again?
Switching resets the light circuit in the controller, so the LEDs light briefly. The OP reports it lights only after toggling, not automatically. This behavior aligns with low‑current shutdown of monitored circuits. [Elektroda, Gomes 40, #17127732]
What current does the C5 X7 plate light circuit expect?
About 0.8 A total. “Nominally, two 5 W bulbs are 10 W, that is ~0.8 A. And LEDs? Less than half of that.” That difference triggers the controller’s bulb‑out logic. [Elektroda, Krzysztof Kamienski, #17127861]
What if my replacement LEDs flash once and both sets act the same?
Assume a compatibility issue with the built‑in emulator. The OP received a second set, and it behaved identically. Return them and choose another design or approach. Reputable sellers list compatibility with Citroën/PSA CAN systems. [Elektroda, Gomes 40, #17127732]
Are there legal concerns with LED plate lights on this model?
Yes. A forum member warns that fitting LEDs in place of approved bulbs risks a failed inspection. “By inserting LEDs in place of light bulbs, you risk even losing the registration certificate.” Confirm homologation before modifying lighting. [Elektroda, Szyszkownik Kilkujadek, #17131104]
Can I power the LED modules from a separate feed to avoid errors?
Yes, if you know what you’re doing. One member suggests a dedicated supply so the LED isn’t on the monitored circuit. “An imposing solution is simply a separate power supply for the LED.” Ensure proper fusing and routing. [Elektroda, Marian B, #17128759]
What’s the simplest, safest fix today?
Reinstall OEM bulbs or a homologated equivalent. This restores automatic operation with no errors and avoids legal risk. As another member put it, “give it a rest and put them there, as provided by the manufacturer.” Save LEDs for models designed for them. [Elektroda, Szyszkownik Kilkujadek, #17131104]
