XSeries-forum

Picked up the 4.8 from the dealer today after another couple of days of investigation.

When driving along, the X will randomly start to shut down the electrical systems. First the headunit screen will go off, then the 4x4 light will come on then suspension inactive then trans failure and then the X will jerk intermitently. If you pull over and turn the engine off and try to restart it is completely dead and I mean completely. You won't get any lights come up no turning of the engine nothing.

If you wait about 15 minutes and try the engine again it will sometimes fire up and all will be well again and it won't happen again for weeks.

It went in to Sytner Birmingham when this happenend previously as I had to call BM assistance and the Tech said he thought it could be the alternator playing up. When it went in they tested the alternator and it appeared to be fine but there was a constant whine coming from the alternator belt and they said it was due to 2 jockey pulley's not running true. So they replaced them under warranty and the whine duely went away (that was in October). I also replaced the non standard battery with a brand new BM one.

Since October it has been running like a dream so I thought it must have been the pulley's, but then last Monday it happened again while driving back from Manchester at about 11pm on the M6. Hence it went in to the dealer again. The new battery I fitted in October was toast (coming up with battery unserviceable) so they replaced this for free along with my driver mirror glass and switch panel, but they still can't work out the main reason the X went in for.

The fact that whatever is causing this fried the battery, I am really leading towards the alternator as this is the only thing supplying the power when driving and should be charging the battery at the same time...But I am at a loss...

Any ideas?

I had something similar recently with my Audi S8 -all electrical systems shut down one after the other until the car died. There was no sign of life at all. then suddenly, on cranking it, it started briefly once more before dying again. Turned out to be the Voltage Regulator, sometimes these are integral to the Alternator and cannot be replaced individually, no idea about the X. If the alternator is overcharging, it will certainly damage the battery and could also fry other equipment - I'd be making a fuss at the dealers about an alternator full replacement if you're under warranty, or considering it anyway if not. Sometimes coil packs threw up problems like this with the Audis, again no experience with this with a BMW.

+1 for alternator/regulator. Had almost the same thing happen on a Vauxhall Cavalier Mk3 SRi. Fortunately in those days the only clever (and it being Vauxhall I am being cautious with that word) electronics were in the ECU and it just went into protect mode then shut down. The battery was almost being boiled!

Changed both and all was fine.

+2
My VW at the time smelt of mashed potatoes (the battery boiling) and and died, refilled the battery and away i went. Later to the main Stealer and the thing was charging at something from memory like 21v not 14.4.

Alternator.
My car died while driving down the A1 near Leeds last summer.
Wouldn't start and had to get recovered to home. Turned out to be alternator and a fried battery.
No warnings, nothing, prior to this.

Cheers for the comments. I too believe it is the alternator, but then they have tested it on numerous occasions and each time it is charging perfectly normally. Also, I am a little confused as to when the car starts shutting down and I pull over, turn off the key and it is completely dead, if I wait about 15 minutes and it will spring in to life. If the battery were truly dead, then that would be it....hmmmmm...so confused by this one.

I too would have said the Alternator, but if its not that then could it be an earthing issue? broken or loose earth strap perhaps. just my 2 pence for what they are worth

+5 alternator but worth checking the connections around that area as earthing issues can be a nightmare to find and diagnose, also a lack of load on an alternator will cause the output voltage to rise to over 30v potentially.

As for the 'wait a bit and it works again' thing, most electronics nowadays have a degree of voltage protection built in. This protection may kick in if the supply voltage rises too much and then take a while to reset when you switch it all off again. This will of course only work for a finite number of times before critical failure so do push the dealer to sort ASAP.

Bring back volt meters on the dash, all is forgiven (showing my age too now)

Good luck with getting it sorted

Thanks again for the replies. I did say to the the service manager that if it continues to happen I want BM to replace the alternator even if it appears to be ok as I do honestly feel it is this causing the issue.

Will see how it goes and keep you all posted.

Hope you get it sorted soon Raj ...mine is frustrating the hell out of me at them mo... but we will get there