W204 Erratic activation of external lighting

[clk320x4]

Greetings to everyone,

My recently acquired W204 has begun to activate the external lights randomly when I park and switch off the engine or lock the vehicle. Initially, it pertained to the tail lights. I then unplugged them until I could ascertain the situation, but upon returning home the next night, my fog lights were on. I activated the ignition and started the vehicle, at which point they extinguished. I then shut off the vehicle and secured it, only to have my sidelights activate. I manipulated the light switch, verified that the indicators were off, then switched off the vehicle. At that moment, just the driver's sidelight remained on, prompting me to concede defeat and secure the vehicle. It is peculiar that upon starting the automobile, all functions operate correctly and any erroneous lights extinguish. No dashboard alerts, no sporadic malfunctions.


I ventured out yesterday, and the power was depleted, which I somewhat anticipated. It was left charging for a whole day and night, with the side light on continuously. The automobile was started, and the side light extinguished. Traversed the area and subsequently returned. The automobile is parked, and no lights are illuminated, but I anticipate they may malfunction again soon.

Do you have any suggestions? I have heard that the light switch may be a contributing factor in some instances; but, the problems I am experiencing do not seem to correspond with that explanation. Possibly the SAM?

Any assistance would be appreciated!

[Howard_silver]

I had a same issue, except with a Jeep rather than a Mercedes (which had a Mercedes engine at the time). Following advise from a site, I unplugged the battery overnight, and the error did not reappear.

[alpaco45]

My W204 had it many times; however, since it was always stored in a garage that I often used, I noticed the issue before it resulted in a depleted battery. Merely toggling the light switch to the 'on' position and thereafter returning it to 'off' consistently resolved the issue. I presume the reason is the SAM module that regulates the lighting. Activating and deactivating the lights transmits a new off signal to the SAM. I did not replace the SAM because to few occurrences, and it only activated one side light.

[BenTrevor]

I would also suggest a SAM module.

[ML350_Colin]

Inspect for water infiltration 👍

[Rojoires]

Water infiltration... or a disconnection of the ground connection at some point.