Its a 2005 3.0 Diesel Sport.... it drives fine for the first 10mins then the 4x4 light comes on and then the transmission feels wholly unstable. The next day it does the same again.... fine for 10mins - then problems. In my last thread the transfer box actuator gear was suggested as a cheap fix https://www.ebay.co.uk/itm/For-BMW-...8&clk_rvr_id=1442918600806&afsrc=1&rmvSB=true I've looked around the web and it sounds like it could be this, as there is a clacking noise which continues for about 5seconds after the engine is turned off (in the cabin its seems to come from below the glovebox), this clacking noise is a re-occuring symptom I've read about in relation to the actuator gear. However, the mechanic hooked up his diagnostic yesterday and (although there were lots of fault codes in general) he could not get any codes for, or more importantly couldn't read the transfer box at all. Which is where he is sure the fault lies. The fact he can't read the transfer box is worrying... and then the presence of lots of other fault codes has lead me to other diagnosis on the web which point towards the alternator spiking and causing a lot of problems with the electrics. I can give the actuator gear a try as its cheap enough, any ideas on why there might be a problem in reading the transfer box? Any ideas appreciated.