Strangest electrical problem ever...any suggestions?
 

This has happened three times now and today required I get my car towed...not happy.

If my 2007 X5 4.8 is in slow moving traffic or left idling for 20-30 minutes it will lose all electrical power and shut off. First the ABS warning light comes on, then AWD warning, then transmission warning, then the A/C shuts off, my radar detector will show "low voltage" and the car limps along stuck in one gear until it dies.

Each time it occurs, it's after being stuck in slow moving traffic for 30-40 minutes. The battery is brand new and three weeks ago a specialist looked at my car for four days...no codes, alternator checked out ok, battery ok, and every module tested ok.

The weirdest thing...today when it died, after waiting 2.5 hours for a tow to the dealer, I pushed the start button and the started right up!! So I drove it to the dealer (I was already on my way there to address the suspension air bag leak).

Clearly something is getting warm and causing an electrical problem...when the car cools down it starts up again. The shop manager at BMW said it's probably the alternator...which makes no sense because a) it was already tested, and b) the car started up again when it cooled down after losing all power...batteries don't recharge themselves.

WTF is going on with my car???? So far this summer, over $6K in repairs (oil leak, coolant leak), $2K for new tires, $400 for new battery, and now this air suspension and electrical problem...I'm sure this will cost me dearly. To say I'm pissed is an understatement.

Had the same problem on my 2006 and it turned out to be the Ignition Switch which would short internally when it got hot.

Forgot to include P/N for switch.
61326901961
Just Google the number and you will see what part looks like.

The problem is I can drive 300 miles at speed and never have an issue...only occurs if I get stuck in traffic and I'm creeping along at a slow speed for 30 minutes or so.

BMW called...they said it's the alternator, even though another shop says it tested fine.

Tested fine cold maybe?

Definitely alternator, had very similar issue with my 08 4.8i, replaced alternator and all was fine . I finally sold the car since I got tired of all the things that started to crop up after 100k miles. Sold the car with 134k and got an F15 diesel.

My 4.8i did the same thing. I ended up swapping out the voltage regulator on the back of the alternator in lieu of replacing the entire assembly. Saved about $500.

I have seen this before and my issue was a bad alternator... caveat, it was on my 545

I appreciate all the replies...at least I feel better seeing so many replies saying it's the alternator. Sucks that I have to pay for another repair...that puts me over $10K in repairs that I've paid for this year alone! Had I known I would have sold the POS a long time ago.

Upon further internet reading, it sounds like the voltage regulator. The alternator itself only needs replacing if the bearings are shot...car only has 59K miles. Just called the dealer and told the to NOT replace the alternator. Just another case of them trying to rip me off...$2700 to replace a leaking air bag in the rear suspension and an alternator...what a bunch of crooks.