transmission lamp on on 2002 BMW X5

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My 2002 BMW X5 steptronic transmission lamp is on and it has slowed it's performance. it always moves with 3rd gear, checked all possisble solutions but the lamp has failed to go off.
Please advise the solution to this problem. thanks
(1) Answer
I think that the computer has detected a transmisson fault and has put the trans into a fail-safe mode (the light would indicate that) to try to avoid further damage and get you home or to a BMW specialist to get it checked.
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