help, im getting a trans failure problem

hi, i have recently got myself a bmw 740 e38 with and intermitantly it give a trans failure message, i took it to a garage and he downloaded the faults, it had a couple of old misfire faults an the trans one.
CODE002: 100    Gear monitoring 1 (2nd-4th gear)
does this mean just 2nd and 4th gears have had it and i need a gearbox refub.
the fault doesnt seem to have any reason to it, it has occured about 4 times in 250miles at different times in auto and sport mode, the mechanic said the box felt fine when he was driving it.
i should also ask, there is a low pitched buzzing coming from below the gear selector panel when the car is switched off and the key is removed, is this normal as i have never had an auto before.
thanks and any help would be appreciated
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No it usually means you need a new battery.
The noise is probably the electric fan - check it out.
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Unlikely - it sounds like an electronics thing. These boxes are very sensitive to low volts - I'd first check the various connectors and fuses are clean and making good contact. Might be also worth checking the battery and charging system - when my alternator failed 'trans fail' was the first indication something was wrong as the battery died.

There are a few heater valves that operate after you switch off - could be one of those.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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