check tranny fluid right away it will act like that. theres a plug on the side of tranny where you check and fill, when you fill tranny fill until it runs out of that hole put plug back in, then start x5 let it warm up a bit then check fluid again and top off fluid till it runs out the hole ,then your good to go. alot of auto manufactures don`t use tranny dipsticks anymore due to people over filling the tranny with fluid .

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2003 bmw x5 3.0i ,219000km build date 2003-08-18