the oil indicator lights in a yellow after every 1900km,no leak at all. on 2005 BMW 325i

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i went to bmw service center with my problem which is the oil indicator lights in a yellow after 1900km..when i check the oil level i found it needs about 1k..and there is no leaking at all checked by the service center,,they dont know what is the problem at all...dose any body has the same (no leaking at all) i dont know where the oil gose,,,,
(1) Answer
(1) Comments
The service center should have checked faults.

The yellow oil can indicator indicates a fault in the system, if the oil level is ok, the oil level sensor is faulty and open circuiting
The oil level is low after the light flash In yellow when I checked the level it needs about 1 kilo ... I think it's not the faulty light cause the oil level is low... And I don't want them to open the motor cover to see what's going on ... Really don't know