E39 530d: Gotta have a teething problem - Drivers Windows Switch

The car has been better than good so far. It drives superbly, is quiet and refined, swift and economical - the 3.0 litre diesel engine is incredible, managing 184bhp and still getting me comfortably over 40mpg for my work runs! A far cry from topping up the Scooby tank by at least £40 every week, but not a world away from the horse-power... go figure.

The only fault I have to report though is a faulty driver's window switch unit. It worked fine for the first few days, then became sporadic and finally stopped working altogether. I tried it on my way home from work this evening and to my surprise it went down. Unfortunately it wouldn't come up again so I was forced to figure the problem out tonight. I drove around for a while in the hope that it would reactivate, but the window didn't budge an inch. I used up half a roll of black-tape sticking a bag over the open window on the windiest night of the year, only to then discover that the windows can operated from the remote key-fob. A genius feature of the techy BMW is that holding down the lock button will close any open windows and turn any electrics off. Holding the boot-release button causes all four windows to go down. I am impressed and very relieved!

The likely culprit was the switch-unit, but I prized it off to find 3 separate wiring harnesses leading to it - one each for the front 2 windows, rear 2 windows and the rear child-lock, so I became worried that the problem was elsewhere is the electronics system. The door-hinge wiring harness was a possibility - apparently they're prone to splitting and getting corroded - or worse still the car's brain - the GM5 computer, which controls the ABS, door-locks, windows, air-con, basically every electronic gadget and these are pricey to replace.

Luckily though, the drivers window responded immediately to the key-fob trick so the GM5 is sending/receiving signals just fine and the door-hinge wiring is still sound. Phew, this means it can only be the window switch-unit - when one circuit in it breaks it must kill all the buttons, regardless of which loom they plug into.

I've found a load of E39 switch-units on eBay around the £25-40 mark so I'll have to get one when I can and see if that puts the window problem to bed. It'll have to wait now though, as my new Angel Eye headlights have just arrived. Get in.