[NiNeTyOne]

Today, while waiting to board the ferry just north of Seattle, I had the car just die, no power, no ability to crank, nothing.

What's odd about this is that there was no prior warning that there was a power issue, nothing on the iDrive, no battery warning light, no voltage warnings, nothing.

The car has been brilliant with little or no issues. The battery was replaced 4 or 5 months ago with a new AGM, properly registered, and driven on an over 4000 mile trip with not even a hiccup.

When I pulled codes after the issue I got a Charging system malfunction code and a couple others relating to voltage on various other subsystems I believe to be related to the charging malfunction.

After the car died I was able to successfully jump the car and drive about 2 blocks before it just shut down having drained the battery flat.

Now with all the complexity in these cars it's a bit hard to diagnose these problems, and I am pretty sure I don't want to leave it to the dealer.

At the moment I am considering a handful of potential issues, notably the IBS, the alternator, and if this car has one, a charging system relay, though I'm not sure if the e91 has one in 2007 (if it could only be a $25 part that would be great). The codes didn't seem to indicate the IBS, but...

My plan right now is to hope the battery tender can get the battery up to a base level of charge, enough to get the car started, so I can read the voltage at the battery with my multimeter and see if the alternator is getting any charge back to it.

If there's no voltage I'll need to look at everything on that bus, starting with the IBS or any other sensors I might be able to unplug. I'm not sure if the IBS is specific by VIN, or if it can be tested, but that might be next.

I've heard that any failure of any sensor on this bus can cause issues, but where to start? Anyone have any expertise debugging these things?

[NiNeTyOne]

Really? Not one person has anything on this?

[GoRomeo]

Did you replace with same battery specs as original? Check for loose connectors.

Do a test on the charging system (alternator) should read about 14.5 when car is running. This can be done at any Auto parts store for free. This indicates the alternator is charging. If you read 12-13v is low, and most likely your alternator is bad.

Starter could be another step to follow but not till you test the above...

[NiNeTyOne]

Originally Posted by GoRomeo

Did you replace with same battery specs as original? Check for loose connectors.

Do a test on the charging system (alternator) should read about 14.5 when car is running. This can be done at any Auto parts store for free. This indicates the alternator is charging. If you read 12-13v is low, and most likely your alternator is bad.

Starter could be another step to follow but not till you test the above...

Starter is good, the car will start if jumped, just won't stay running.

I'm pulling the battery and having it tested, it was the same battery that was coded to the car previously and I registered the new one myself.

If the battery is bad, I'm pulling the alternator. Once I got the car jumped this am, I was able to pull new codes, and 002E98 came up, which is Generator Communications, so I'm thinking shorted battery or as you suggest, alternator or regulator... may as well swap both with a lifetime reman if that's the case.

Will update.

[NiNeTyOne]

Battery was okay, but it was dead flat with zero charge on it, so they replaced it under warranty anyway which was awesome. Brand new 92aH AGM installed, registered and good to go. Cleared codes, started the car, ran the codes again, and sure enough generator communications error.

Tested the Alternator at the leads and at the battery and was reading 12.2v so it's dead. Shop has a reman'd Bosch unit for $269 with a lifetime warranty so I picked that up, swapped it out in about 10 min and then cleared codes, and it's all good.

No codes, and it's putting out 13.6v

I would have been happier with 14.2-14.5v so I called the shop and they are getting another new alternator for me and will test it when it arrives mid week. If it's putting out 14.x I'll swap it out for that one since it's such a simple job.

Only PITA is the one use aluminum bolts are $20 from the dealer so I'll be buying another set.

[PhaseP]

The alternator voltage output is regulated by the car computer and it changes it based on the battery charge. On an already charged battery it would put out 13.6-13.8v. If car had drained some charge like sitting overnight it would put out above 14v initially after computer decides it charged the battery full then slowly go down to 13.6 or so.
This is why registering a new battery and keeping battery Ah and type same (or reprogram) is important after battery replacement. In short 13.6v alternator output on these cars doesn't necessarily mean bad alternator.

[Wilt]

Originally Posted by PhaseP

The alternator voltage output is regulated by the car computer and it changes it based on the battery charge. On an already charged battery it would put out 13.6-13.8v. If car had drained some charge like sitting overnight it would put out above 14v initially after computer decides it charged the battery full then slowly go down to 13.6 or so.
This is why registering a new battery and keeping battery Ah and type same (or reprogram) is important after battery replacement. In short 13.6v alternator output on these cars doesn't necessarily mean bad alternator.

^
The IBS commands the voltage from the alternator/VR, so alternator and VR could both be fine, yet they might not output the proper voltage. Voltage output commanced by IBS is based upon multiple parameters, including battery temperature.