I had the dreaded 2-1 downshift knock and after a fluid change it did get better but only temporarily. Ultimately you're facing a transmission refurb, sorry to say. The mechatronics is fine. The knock is caused by worn bushings creating excessive play in the transmission shaft. I ran with my knocking problems for around 50,000 kms before finally getting it refurbed. Mine is a 2006 X5 E53 3.0D 6HP26. Issues started at 110,000 kms.


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