w212 battery drain

[w212e350cdi]

Hi all, i have an e350 cdi W212 (S212) estate. Having battery drain issues which started with the tail lights coming on when parked. I seem to have rectified that issue but still having battery drain. While charging the battery i noticed a buzz from the engine bay that never dies. Going through the fuses to kill it its fuse 27 which controls

Valid for gasoline engine: ME-SFI control unit	7.5
Valid for diesel engine:
CDI control unit
Electronic ignition lock control unit
Valid for engine 271.958, 274.920: CNG control unit

If i replace the fuse the buzzing is gone but it comes back when i start and turn off the engine. Pulling the fuse to kill the sound and replacing straight away, then leaving over night the car started in the morning so im assuming this is the cause of the drain and usually it was dead in the am.

Any help appreciated.

 

[bembo449]

Does pulling the fuse stop the drain on the battery ??

 

[w212e350cdi]

Does pulling the fuse stop the drain on the battery ??

Hi Bembo it seems to. When i dont pull the fuse the battery will be dead in the morning. If i do pull it the noise will stop and wont come on again when i replace it. (unless i was to start the car again). And the battery would be ok in the morning and would start the car.

The noise will be there hours later so not the evap or a fan as i have been reading on forums.

 

[bembo449]

It seems obvious that whatever unit controls that noise must be faulty then