Sorry about the situation Fariz..

On another note - this has been happening to me very rare about 1 or 2 - maybe 3 times max.


I'll be driving usually car cooler not warmed up fully, and ill slow down over some train tracks for example by my house, then get back on the gas 2.5ishK rpm - car downshifts like 1/2 gears in D... But i get this power blip - perhaps its due to a going battery or something with the ALT - maybe someone here can provide insight... but the nav screen and radio cut out (off) then come back on about 1-2 sec later.

I'm glad that you, your kids and the X5 went through it safely.

This ^^^ would make me double check the battery cables to make sure they are tight...and also check the battery hold down clamp to make sure that it is clamped over the foot of the battery and screwed down tightly in one of the threaded holes in the battery compartment.

You never know...you may have missed the threaded hole for the battery hold down clamp...thus when you drive over tracks...it moves the battery enough to disturb one or both of the battery cables...causing a brief break in power.

Actually - i was just using the tracks as an example because i slow down then get back on the gas and its a slight incline as well.

I know what you are saying that happened on diff car in past - but i know my cables are tight cause i was just in there the other day cleaning my DSP fuse contacts cause radio went dead.. but batt is in good and cables tight..

This happend to me the 2nd time was on flat road but again blipping the throttle.

To me it seems something with alt/batt.

Wow, glad you all came out ok.

Now, I am curious, is BMW supposed to shut off with the battery disconnected. What gives. I had multiple non BMW cars with the battery disconnected to test if the alternator works, a crude test, but a quick and easy one. Why did the car shut off?

Thank you guys... really appreciate the concerns... :)

to Denis - this confused me as well... I can't call myself a mechanic but was around the cars since my grandma's '68 "moskvich 408" and i remember that once the car was running, you could take off battery terminal (klemma) and the car continued to run, off the alternator juice. it would not restart, once shut off, but would not shut off... this is the strange thing that i was talking about in the original post... the master kill switch cuts off the negative battery cable... maybe the alternator's negative lead is not grounded to the rest of the car but ran directly to the battery? not sure how this can be done in this particular application... strange indeed...

Patrick - in your case i would still check the cables in the trunk, not just the battery cables but also to see how tight the connections on the master fuses on the back wall of the trunk cavity and make sure that the nuts on the ground cables are tight too... from my experience/experiment it is evident, that the car may have a tendency to shut off (or just a hiccup) if the master power is disrupted...

Ok, but there is no negative lead. Only a positive, negative is through the metal in the engine and car. The are some negative wires, but not at the alternator. I had it out when I rebuilt it.

Have you tried running test 9 in obc to check voltage. Maybe your alternator is not producing what your car needs. You do have a shit load of extra goodies in your car that we don't.

lol... you got me on the shitload of extra goodies!!!... lol...

the culprit was indeed the switch - the car was in complete darkness without any signs of life... once i reached in and flipped the switch (which was in OFF position), the whole car came to life - the lights (engine off, no headlights, but the perimeter lights), the inside lights, the radio...everything... the car started right up, no hesitation... drove, like nothing has happened...

I will monitor the alternator output, as well as other external symptoms - I do not know well a car can take a sudden loss of power midflight...

it reminded me that movie, Avatar, when the dude in the wheelchair was yanked off the remote connection to the green/blue man, and the green/blue alien just dropped like a sack of potatoes... and then he reconnected, shook off the dust, and off he went...

I understand the concept of chassis/ground - the negative lead of the battery is connected to the "masse" and you pick up the negative anywhere else in the car off the chassis... same goes for the alternator... as you notice, the ground cable is actually tied to the chassis... as well as numerous ground "combs"...

from the studying the prints it is evident that the master switch is severing the return loop to the battery - it is the ultimate junction point for all the electrical wiring fed by the car's battery... (in absence of a secondary battery... which makes me think.... hmm... i need to get to drawing board):thumbup:

Don't recall what tranny you have, but I'd be concerned about the loss of electrical power to an automatic transmission while "in use". Glad you and the kids stayed safe though.

2002 X5 3.0 247,800 miles
2004 325i 110,000 miles

it is a 6-speed auto - 2006 4.8is... i never thought of it but this is a good point... i will monitor the performance and will connect INPA to see if there are any codes...