My car is an E60 525d lci and in about 9000km the battery died 3 times without any notice while driving. I unplugged the IBS sensor and started monitoring the battery voltage ever since and it seems that sometimes wheb the car starts the battery is not charging at all and it would stay like this until I turn It off and on again. Any ideas?

 

Have your alternator tested. It seems like it's having intermittent issues.

 

Check for a bad ground strap from your body to engine block. You might be losing the ground connection to the engine (and therefore the alternator), which could be intermittent.

Otherwise, I'd try monitoring the charging voltage (should be 13.8 volts, plus or minus a few tenths) while wiggling the cables going to the alternator, so see if you can induce a "failure". Otherwise, it sure sounds like a bad alternator - you can probably replace the regulator, or maybe just get a new or refurbished alternator (I swapped mine out at about 130,000 miles because I didn't like the sound of the bearings using a mechanic's stethoscope).

 

I have been monitoring it constantly for a few months using the “secret menu” readings. Voltage is 14.2/14.3 constantly while charging and 12.0-12.6 (decreasing slowly) while not charging - the latter does not budge with RPMs.

I need to mention that I can turn it off and on over 10 times in a row for it to start charging properly. Seems like a weird issue and I do not want to start changing good parts.

 

It could certainly be the alternator, but could be cabling as well (with the "hit and miss" effect being due to the slight movement of the engine relative to the chassis anchor points for the cables heading to the alternator, or the ground strap).

I'd say that you might be able to chase down the culprit if you can get the charging system to act up and then - while monitoring the voltage - wiggle those cables going to the alternator, and maybe jumper-cabling the chassis to the engine block (to simulate a good ground strap). You just might find something loose.

 

Thank you! it just happens that it’s been only acting up lately, I turned it off/on 15 times and it doesn’t charge anymore. I doubt I will drive it anymore anyway. Are the cables going to the alternator safe to wiggle with the engine on?

If I don’t find anything loose is there another way to test a bad alternator without getting it out?

Do you recommend I refurbish this one or buy a good used one instead - New one is out of question for me.

 

The alternator has a variable output. The car's computer tells it how much to output depending on what it thinks by communicating with the alternator over the BSD data link (also shared with a few other devices in the car). So, if you don't have any specific issues other than noticing this voltage difference, it may be completely normal and as designed.

 

Is that handled by the IBS on the negative battery terminal? If so I have disconnected it recently thinking that could be faulty.

I have 11.9V right now with the engine on, so I assume the battery will die very soon. So yes I think there is indeed an issue - as I said it happened before that the battery dies.

 

Voltage changing is normal, though having it drop to 12 volts or below with the engine running isn't. ;-)

I just went through my E60 power management service document, and "it's more complicated" than I thought, with the DME being a pretty large part of the secret sauce that makes a BMW alternator wake up and start working (it contains the "programming" to tell it what to do). The IBS does provide some info, though I wouldn't swear it could cause the symptoms you're seeing. Is the IBS still unplugged?

I can send you the service document so you can get a feel for just how complicated BMW has made the charging / electrical load systems in these cars (kind of astonishing). The document is about 700kb in size (I think that's OK to send as an attachment in the messaging function here).

That said, the most common failure IS with an alternator, and my "wiggling cables" is still a very valid suggestion. If you can cause the symptom to cut in and out by moving a given cable, you're close to finding the culprit.

 

Sure, send it please, I could use any help. Also can you confirm that it’s safe to wiggle the alternator cables? What you are suggesting sounds pretty promising.