2004 X5 4.4 (N62) Battery/Voltage issues

[TerraPhantm]

So this is actually about my neighbor's car, he asked me to take a look at it since it was giving transmission failsafe errors and occasionally not starting if left for a few days, and I'm kinda known as the BMW guy around here.

So first thing I checked was the error codes. Lots of low voltage errors stored in pretty much every module. And oddly one high voltage error (18v).

Next I voltage while the car was running. It was at 14v for the most part, but occasionally it would dip down to about 11v (battery voltage) while idling. Battery light never came on. Increasing load (defroster, heated seats, etc) seemed to keep the voltage steady at 14v. Voltage was also a steady 14v while driving. I know the alternator communicates with the DME on these newer DMEs, so I don't know if the altnernator briefly cutting out is by design, especially since the light never came on.

Next I charged up the battery until my charger indicated full (battery voltage was reading about 13 iirc) and left the car alone over the weekend. Came home and the battery was 6v. So I'm thinking parasitic drain. I charge up the battery again, hook up my multimeter, and checked the current after it goes into sleep mode. About 36mA which seems normal to me. Using the min/max mode it looks like it went as high as 92mA, which might be technically out of spec, but idk if that's enough to drain a battery so quickly. And the average is still 36mA.

So the battery doesn't appear to be original, but I guess it is probably dying/dead if it dropped to 6v, so I will ask him to replace the battery. Since there were some voltage errors stored too, I'm thinking the alternator could be bad (even though it wasn't really acting up in my possession). Is there anything else I should look for that's common on these X5s?

[David.X5]

I'll second trader4 - either do a load test at home or take the battery somewhere that will load test it off the car.

If the battery drain is really staying that low (and not increasing in the middle of the night for some random reason), I think a healthy battery would be fine for several days.

If the battery checks out, then next for me would be the alternator and voltage regulator.

About the drain - if the car has aftermarket electronics - alarm, radio, etc try to disconnect those and see if it helps. They seem to be the most common source of mystery battery drains.

[jgold47]

Hola Terra.

The e53 was basically built over the bones of an e39. So its not that dissimilar to the e46 You're a jedi on the E46, so go with your instincts.

It seems the GM3 seems to be even more voltage sensitive than the GM5

I'd start with a new battery.

[X5only]

It sounds your case may be the battery, but I had similar issues with my 4.4 N62 and in my case it was the alternator. I always got faulty alternator code including low voltage codes for nearly every module, but, strangely, no alternator light! The alternator wasn't charging the battery fully and it would intermittently cut out. It was very dangerous as the car could die on the freeway - it did that once and really freaked me out. I replaced the alternator (about $300 for a rebuilt one) and battery. All has been well since.

[crystalworks]

^ I can also second (or whatever number we are up to) the advice given. I had these exact issues with intermittent voltage and battery dying over short period. Not as quickly as the one you are working on... but still annoying. Trans and undervoltage codes were being thrown. Replaced battery and alternator. Fine since. Battery was ~$160 and alternator was ~$250 (rebuilt Valeo unit). Both from Oreilly's.

Be aware though... I had to get 2 alternators before we got a good one. First one had a bad VR. Took ~3 hours the first time to install and the second time only took about an hour with two people. Very easy job.

1. Remove electric fan.
2. Remove belt (T45 torx on tensioner)
3. Remove idler pulley on alternator (T45 torx)
4. Remove 2 16mm bolts on alternator
5. Slide alternator forward until plug and large battery cable are accessible.
6. Unplug harness and remove 13mm nut on the battery cable. Remember orientation.
7. Carefully slide the alternator up through the top. Not able to get out of the bottom. Be careful with radiator fins.
8. Install new alternator in the reverse order.

Tip: Removing bottom splash shield may help with access from bottom if you have to rotate the alternator or other tasks. Mine was off already and we did use access from underneath a few times.