Near Total Electrical Failure

[JeffD]

Yesterday afternoon I noticed the Check Engine light come on when I started on a short trip of about 4 miles. There was about 18 miles of range remaining on the battery and about 65 miles on the Rex, and the Rex hasn't activated since the last maintenance run about two weeks ago, and didn't activate on this trip.

After I parked my car and had been at my destination for about an hour, the car suddenly started blaring the alarm and my key fob wouldn't shut it off. It finally went off on its own.

I went to drive back home and the car wouldn't activate. A couple of interior lights would come on when I opened the door, but neither the shifter lights nor the instrument panel lights would come on. My key fob would not lock or unlock the door, nor would the door lock/unlock button on the door activate the door locks. Nothing worked except for a few small lights, like the glove box light or the door handle lights. I though the key fob may have lost its battery, so I got the second key fob from my wife and it wouldn't activate anything either.

I put the car charger on (after having to pull the emergency charging port door release), but the charging port light didn't come on even though the charger lights indicated a good charging status.

After being on the charger overnight, there is no change in status. Does anyone have any ideas what may be the cause of this situation?

Thanks

 

[jadnashuanh]

Your 12vdc battery may be toast. Normally, it is recharged by the main batteries via a DC-DC converter. But, if it is way gone, when you plug it into an EVSE, there is an emergency 12vdc trickle charger. That may or may not charge the 12vdc battery enough to make things return to normal. THat whole procedure can take many hours, but overnight, if it is the battery, it would have likely worked.

So, you could pull the HV disconnect, remove the 12vdc battery and take it somewhere to be checked, or, if you have a fancier battery charger, put that on the now disconnected battery and see if it can revive your battery. If it's bad, replace it. If it's good, you'll probably have to have it towed to a dealer for them to diagnose your problem.

All of the computers essentially run off of 12vdc, so if that battery is bad, you won't be able to start things up.

 

[vreihen]

When in doubt, the 12V aux battery failing (3-4 year typical lifetime) causes all kinds of weird electronic gremlins.....

 

[alohart]

You almost certainly need to replace the 12 V battery. If you are able to do this yourself, you'd save a couple hundred dollars over what a BMW dealer would charge. You could buy a replacement battery at a BMW dealer, but you'd pay over $50 more than if you bought the same battery, an AUX18L, from a local East Penn Manufacturing dealer.

 

[JeffD]

Thanks, a 12V system failure does sound like that would result in the behavior I see. I actually am still under BMW Roadside Assist and warranty, so I was able to get it towed to the dealership and they are on it now. I'm assured that everything, except for a possible diagnostic charge, will be covered by my warranty. The intake person at the dealer had never seen the behavior the car exhibits, but I'm hoping it's actually something as simple as the 12V battery.

Forgot o post this earlier. Just got a call from the BMW dealer and it is the 12V batter. My question is why did this fail so catastrophically? The car behaved fine on the way to my 4 mile trip and then was totally dead when I was ready to go two hours later. And the car's main battery wouldn't provide any level of charging. Seems like with all the indicators and sensors, there should be one for this.

 

[eNate]

I wouldn't call it catastrophic failure, just a routine failure with catastrophic (yet predictable, known!) results. Crazy, ain't it?

And with all the discussion of the necessity to "register" fresh 12v batteries so the i3's super-intelligent brain can systematically track the performance trends of this oh-so-critical component to the car's life force -- like an overweight pacemaker -- extracting peak performance from it while new yet treating it gently like a fragile eggshell when it's aged, what do we get when it comes time to put it to pasture? An alert from our Connected app? A warning chime and a pop up message on the dash? A call from BMW to schedule service immediately? Nope, we come back to a car that's experiencing a grand mal seizure.

Thanks, BMW.

 

[Anonymous]

Seems like with all the indicators and sensors, there should be one for this.

You'd think. But since the 12 volt battery is what turns on/powers up all the ECU's in the car, ie. all the computers that control everything - when the 12 v
dies, no power to the car's 'brains'. The car can draw power from the HV traction battery, but only if the 12v battery powers up/turns on the DC/DC converter first. :ugeek:

 

[Bertone]

What's the price at the dealer of the 12v battery?

Is it mandatory to reprogram it?
Or is it sufficient just to swap in the new one?

 

[JeffD]

Yes, the battery must be registered with the car's ECU, which monitors and regulates current and charging. I don't have the equipment for that, but for the price the dealer is charging, I could buy a tool, like a Foxwell scanner, and still come out better.

I understand that the 12V battery is needed to operate the diagnostics, but I still think they should provide an indicator that tells me that I'd better replace the 12V battery before the thing fails this catastrophically.

And yes, I consider this a catastrophic failure, which is defined as: A catastrophic failure is a sudden and total failure from which recovery is impossible.

If I have to get the thing towed, that's pretty catastrophic. In the end it's a minor component failure and relatively low cost to recover, but not field recoverable.

 

[jadnashuanh]

Around here, PepBoys will register the battery for about $35.

 

[eNate]

... I consider this a catastrophic failure, which is defined as: ...

Maybe the point I was making was too subtle.

Look, it's not like the battery imploded or went supernova. It's deteriorating with time and use, just like every other battery is expected to do. The battery didn't catastrophically fail.

The fact that it reaches some magic voltage threshold where the i3 bricks itself, sure, I'll agree that can be a catastrophe for the owner, but it's ridiculous that BMW designed a system that allows it to get to this state. Can you have a "planned catastrophe" that every single i3 will go through unless the 12v battery is preemptively changed? I don't think so.

Again, the battery is decaying normally, predictably, and measurably, just like every other battery.

So back to my point about the super-important registration (it's not). If the system was actually monitoring battery health as it ages (it's not), the car would most certainly flash a maintenance warning to owner before ever getting to such a state (it doesn't).

FWIW, my 2013 Audi "required" battery registration, and that system flashes a "weak battery" message when it's time to swap in a transplant. If Audi can do that on an entry level A4 variant with an ECU that predates the i3, why can't BMW incorporate that same feature in a car that depends on the battery?

And FWIWx2, I neglected to register the Audi battery -- also an AGM type -- and instead connected a 12v charger and performed a hot swap, like for like. No ill effects suffered in the remaining 3 years I owned that car.

That's all I'm saying.

 

[alohart]

The fact that it reaches some magic voltage threshold where the i3 bricks itself, sure, I'll agree that can be a catastrophe for the owner, but it's ridiculous that BMW designed a system that allows it to get to this state.

For what it's worth, our 2000 Honda Insight hybrid suffered the same problem as our i3: when its 12 V battery's voltage dropped below a certain threshold, the modules necessary to enter drive mode would not boot making the car undrivable. No warning was displayed in advance of this happening. It's great that Audi seems to be able to display a suitable warning. The i3 also does this in certain situations.

The problem with displaying a warning might be that the i3's 12 V system voltage drops so much when the high-voltage system turns on (e.g., when unlocking or opening the driver's door) that it might drop below the threshold below which modules can't finish booting even though the 12 V battery's resting voltage isn't dangerously low. While the high-voltage system is booting in our i3, the 12 V system voltage can drop as low as 11.9 V before the DC-DC converter turns on even though the resting voltage of the 12 V battery is >12.5 V. When I first measured this, I was certain that the 12 V battery was failing so asked our BMW dealer to check it during our upcoming scheduled maintenance visit. The service manager told me that this is typical i3 behavior and that our 12 V battery tested normal. 2.5 years later, our original 12 V battery still hasn't failed.

 

[eNate]

Real time, I'm with you -- the system can't tell you the battery is kaput if the system is powered by said battery.

But what the system should be capable of is monitoring trends, and tracking simple metrics such a the voltage at boot or immediately after boot, or the net current into the 12v system to return it to "charged" status, or the time it takes to get it there. Maybe even temperature?

Some of this is rudimentary and some is more advanced ledger-type monitoring, but they'd be the same bucket of tricks that the system uses to monitor the HV battery. AGM battery have a flatter discharge curve than lead acid, but it's an established technology.

And before that downward trend reaches that oh-so-predictable threshold, it flags the user. Hopefully weeks or even months prematurely, not the day of.

 

[JeffD]

Good tip about Pep Boys. I guess I should just plan on a new battery every 3 years.

 

[jfran2]

FWIW, I just replaced the 12v battery in my 2014 Rex. The Foxwell 510 scanner I bought to register the battery wouldn't do it - I ended up returning it. Downloaded Bimmerlink and bought a Bluetooth dongle, which handled the job easily.