What can you tell me about battery management systems?

"Urambo Tauro" (urambotauro)
10/09/2018 at 21:00 • Filed to: wrenching, batteries, battery management, battery management system

Found this while tracking down an electrical problem on my brother’s 2016 Focus. What can you tell me about it?

My brother (not the one with the Saab, different brother) just had to replace his battery shortly after it was given a clean bill of health from Belle Tire and AutoZone. It wasn’t until I had removed the battery from the car and taken it in for a second third opinion that somebody could confirm that it was junk.

When the battery is in the car, the negative end is hidden, tucked away under the cowl, where this little module thing attaches to the negative post. It’s a non-serviceable, integrated part of the negative cable, which bolts to a nearby part of the frame where there’s a stud that you can clamp onto for jump-starting or testing. The module connects to the wiring harness via a two-pin connector.

After my brother left, I did some googling on the part number “AV6N 10C679 BF” on the sticker. Sure enough, Ford considers this whole assembly- including both the cable and this mystery component- to be one “part”. Most search results simply call the whole thing a “battery cable”, but I did find a few listings calling it a “Battery Management System”, which sure is a mouthful for what is surely only part of that management system.

I don’t wrench newer cars very much, but I have heard of these systems, and I’m ready to learn more about them. What can you tell me?

My initial research informs me that my brother’s new battery needs to be complemented with a reset of the Battery Management System. I suppose disconnecting the battery isn’t enough to accomplish that. Is there a DIY method to resetting it, or does it have to be taken to a dealer?

H8QTB SW2.4 AV6N 10C679 BF

As for that module, I gotta admit I don’t recognize the shape of it. I can see a strip of copper carrying the circuit through the plastic box. What’s inside there? Resettable circuit breaker? Temperature sensor?

Oh and BTW, these are the only pics I remembered to take, so here’s a !!!error: Indecipherable SUB-paragraph formatting!!! to see more of what I’m talking about.

DISCUSSION (5)

nj959 > Urambo Tauro
10/09/2018 at 22:36

I did some research, and I was able to find this:

Jayvincent > Urambo Tauro
10/09/2018 at 22:38

google led me to this:

For a reset of the BMS:
1. Switch on ignition (do not start engine)
2. Switch on dipped beam
3. Press 5x the rear fog light button (do not switch 5x on and off the rear fog light)
4. Press 3x hazard lights button (do not switch 3x on and off hazard lights)
5. Then the battery symbol in the speedometer should flash 3x quickly.
If it does not flash immediately, wait 20 seconds.

link here: https://www.focusfanatics.com/forum/mk3-focus/752153-battery-change-bms-reset-2.html

I have a US SE without start/stop and mine has a BMS and can be reset. not sure about this method though seeing as US versions don’t have a rear fog light switch. maybe you mean defroster?

sure fire way is to do it with forscan service procedure “reset battery monitor system” and follow on-screen prompts.

Alternatively you can disconnect (positive and negative pole) car battery over night.
This also resets BMS.

Urambo Tauro > Jayvincent
10/09/2018 at 22:51

Nice find. I’d seen the suggestion about leaving it disconnected overnight (8 hours, supposedly), but I also saw that method refuted as ineffective. This procedure sounds more legitimate, but I’m not sure about that fog lamp button part. I’ll send it to my brother anyway for him to try out.

If that doesn’t work, the FORScan option sounds interesting...

AMGtech - now with more recalls! > Urambo Tauro
10/09/2018 at 23:39

I don’t know about Ford’s in particular. But modern cars can have a few different things attached to their batteries that look similar to that. Pyrofuses, that go open in the even of a crash, triggered by the airbag module. Standard fuses that blow in the event of over-amperage. Voltage sensors. Relays/voltage-dip-limiters that trigger auxiliary batteries to kick in when the engine is shut off.

Your device doesn’t look complex enough to be an actual control module to me, it looks like it might only have two pins. The connector is wrong for a pyrofuse, so I don’t think it’s that. I think it’s a voltage sensor that sends it’s information to an actual control module, largely for determining if it’s safe to shut the engine off and how much the alternator should be charging.

A BMS usually needs to be told it has a new battery because it can change it’s alternator and start/stop logic/protocols accordingly. If not reset, it may charge the new battery in such a way that it’s life expectancy is reduced, or result in an improper power supply to sensitive modules.

Urambo Tauro > AMGtech - now with more recalls!
10/10/2018 at 00:29

I realized after reviewing these pics that there’s also a number stamped directly into the plastic next to that sticker. I can’t read it from here, but maybe that’s something that could have been looked it up on DigiKey or something.

The connector does indeed have two pins, and I forget what the wire colors were for it. I want to say that one was white, and the other purple. Not that that helps much. I can’t find wiring diagrams for this car, at least not without purchasing a Ford service manual or signing up for a service like ALLDATA. I did find one suggestion saying that it was a dedicated ground for the ECU and other modules, but the wire coloring suggests otherwise anyway. I’m thinking it’s probably a sensor.

Whatever it is, I’m going to try to get my brother to get that BMS reset done ASAP.