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Battery drain issue - BCM

somubtech

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#1
2018 Ford Fiesta S hatchback.

My car suddenly started draining battery in 2-3 days from full charge to flat. I watched lots of videos and did some diagnostics with multimeter- battery is fine & holds charge and alternator is fine too. When car is OFF .. it’s drawing 260mA. I tried parasitic drain diagnostics by removing 1 fuse at a time and noticed when I remove the BCM fuse current draw drops to 120mA. I couldn't figure out what else is leaking current (or could it be the faulty bcm is somehow drawing the remaining 120mA too??)

I’m trying to find the replacement part - model number - DN1Z-15K600-S ( found this number on internet) but can’t find it anywhere online .. is this the correct part ? Is there any equivalent model I can use?

Any suggestions appreciated!! Thanks a lot
 

Handy Andy

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#2
The battery drain test can be re-performed at about 5 minutes AFTER the first test to determine the drain is consistent.

I would only pull fuses if the tests you try - are failing due to the extra draw to help localize the issue - you seem to have gotten the BCM - so did you check to see if the power supplied by the BCM to the auxiliary systems it supplies are not left on by error?

The car (for the draw testing) is left in the "state it was in for the 1st reading" albeit the door open or interior light on - the issue here is to make sure the same conditions are being used for the tests to be completed.

This extra draw may mean you have a blown bulb, for the interior lighting is also thru the BCM - so make sure the system - if it's consistent - with the drain reading - better check the lamps too.

Why? The BCM usually tries to do a battery monitor kill if the draw is excessive - like it thinks you left a light on - but if the lamps are small 194 types or you use LED it may not be able to sense the current draw correctly and just let it kill the battery never knowing why - so be sure you check the bulbs too - for they go thru the BCM for power and also their timer function of "On XX minutes after Parked" moments.
 
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somubtech

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Thread Starter #3
@Handy Andy Thank you so much for your inputs. I did the test, and 5 minutes after the 1st test and the results are consistent.. I made sure everything is off, I also pulled out the USB stick, phone charger in the lighter, and nothing is plugged in and no after market accessories or lights.

I did a more thorough testing this time... I was able to test out both main fuse and the one in the passenger compartment. Current draw is constant at 250mA. When I pull out F10 (BCM. Right-hand exterior lamps) the current draw drops to 130mA. And pulling out F11 (BCM. Left-hand exterior lamps) drops another 10mA to 120mA.. this is the lowest reading I could get.. I removed one fuse after another one in main panel & passenger side.. and the current reading is not impacted. I could not pull out the relays (large black ones). Is there any use it trying those?

Regarding bulbs - I checked all the bulbs .. everything looks ok. When I shut the door, for example the trunk, i did notice the lights did go OFF.. I am clueless right now. My main concern is, what is drawing the remaining 120mA ? Besides the fuse in both panels.. is there anything I missed to check?

Any suggestions/advice highly appreciated! Thanks!
 

Handy Andy

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#4
How is the Alternator doing?

IF it's been the original since you've got it. I think it should be tested or at least inspected.

Why?

Starter and Alternator - are the only other two "sub systems" that might need access to the BCM to handle Regulation and to also provide starter inhibit or enable to prevent theft - an alarm system - called PATS if you have such a system on the vehicle.

The alternator I would be concerned if the Diode Trio - a set of Diodes used as rectifiers to take the STATOR output coils from AC current spinning causing the the ROTOR and turn it into DC power to supply the system and re-charge the battery..

The BCM supplies the Alternator with a regulation signal - and also uses this signal in part of it's LIN (Local Information (or Inquiry) Network).

You may also want to try to listen to the AM radio for noises that seem to affect reception - like spark plug and or alternator whine - test with engine on running and off to listen to this ambient noise level. This can provide a clue or two on the condition of the electrical system - even the condition of the battery.

But if you say the alternator is Ok, the only way to check that is to disconnected the alternator overnight and recheck the battery "float level" the next morning - if that was part of your check - and you still had battery drain issues - then we can skip forward.

Now you did mention fuses that changed the draw - being the exterior lamps - so that brings up a question about the side mirror - do you have lighted side mirror turn signal?

The 120mA seems high - even to run a clock or keep the APIM screen up or SYNC talking to the subsystems trying to say "goodnight" or "Up for a Card Game?)

So the only other options are there may be a failure in the battery in itself - the construction of it - two adjacent cells may be forming a crack and electrolyte is seeping and or forming a conductive bridge of exchanged ions that will force a 12V battery to drop to a 10V POS over a short time.

Have seen several failed batteries - brand new - just get bounced in a severe bump and by their sheer weight the internal integrity fails and cracks - so the battery loses two (or more) cells - they short together (the crack forms and so the insulation fails) to form one cell at 1.2V and no longer pile together in series - instead the cells are paralleled together - dropping the battery to near flat because of the conductivity of the electrolyte during charging keeps it high enough but it falls to a set voltage and remains there - because of the shorted cells caused by the cracks in the case casing letting the electrolyte and cells see each other and conduct as a single unit instead of a battery pile in parallel to the ion exchange occurs and they work as one big pile - not individual cells.
 
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somubtech

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Thread Starter #5
@Handy Andy Thank you so much Andy! Couple of weeks ago I got my battery checked at Autozone. I was told the battery, CCA, and the alternator are good. Again, at home, I checked if alternator is producing enough power to charge the batteries, it was indeed generating 14.5V. So I concluded alternator was not part of the issue.

As per your explanation, if alternator diode is an issue, it would still pass autozone check? I tried to do AC voltage check with engine running.. and I read 34.5 mV AC across battery terminals when car in idle. I am not sure if it is out of range. I am in process of figuring out how to disconnect the alternator from the battery.. I will do that asap.

Regarding side mirror, there are no lights on the mirror. Also doubled check headlamps and fog lights.. they are working fine and they oFF after 10 seconds. There are no lights on the door itself so if there is a door latch problem, all I could think of is dome lights in the car could come ON.. but all those lights are OFF. Trunk light is off too, and no lights on the number plate. No light under the bonnet.

Cracks in the battery.. if that could be the issue, for the past 2 weeks, I have been keeping the battery disconnected.. so I dont let the car drain it.. and it seems to hold up ok. I occasionally connect the battery to do the parasitic current draw tests.. now working on the testing the alternator itself..

I think for now, I will try the alternator diagnosis, and if that comes out clean.. I will get a new battery and see if that fixes the problem.

One question for now.. is 34.5 mV AC when car in idle, is it normal ? Or does it clearly indicate issue with a faulty diode?

Thanks!
 

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#6
The easiest way to check for Alternator battery drain is to simply disconnect the alternators main post and install connect that Multi-tester, set it to 10A and make sure it's got a fuse in it - to act as the in-line sense - so when you do this, you do this with the engine off - doors closed - key out and then pull the alternator terminal at the battery, then install one test lead of the tester to battery terminal - the other line to the output side of the alternator - the wire with the lug to that post.

The 10A fuse might blow - if it does blow, then you certainly know you have a bad alternator. Took a lot of current back to the diodes and blew the fuse to protect the meter.

You can also use a simple voltage tester - the one with the "Gator clip" and the filament light (not the LED one) - pull the Alternators charging wire off the battery positive post and put the tester in line from the battery to the alternator wire - if it lights then suspect the Alternators Didoes are fried or gone leaky.

Back to the multi-tester -

Measure the amperage.
  • - don't see any?
  • - starting backing down the scale 2A then to 200mA
  • - if no change (zeroes) then the Diodes are fine - the issue is with the BCM - and possibly a bad or shorting cap loading the line down or some issue with the BCM module.
  • IF you do see a condition - is it the same reading as the BCM? - them the "monitor sense line" from the Alternators multi-lead connector that handles the regulation - is telling you the system regulation "loop" is not turning off correctly leaving the system on, so it may be both Alternator and BCM problems together - it will need more diagnostic with a system the full-service department would have to diagnose this.
 
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somubtech

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Thread Starter #7
@Handy Andy Thank you so much for your inputs.. I never did anything beyond an oil change on my car. I am starting to learn more about cars now!!

I tried the alternator battery drain test today (was really hoping that its faulty alternator).. by placing the multimeter in series between the alternator post and the connector and current read 0A (even on 200mA scale).. I went back to the battery and checked the current between the negative terminal.. and I am still getting 240mA. this is very consistent reading. And when I pulled BCM fuse, I am still reading 120-130mA. Is it possible that faulty BCM is somehow causing the remaining 120mA draw even when the fuse is pulled out? I do not mind replacing the BCM but it looks like not a simple swap like alternator, so I wanted to make sure thats the issue, before I proceed..
 

Handy Andy

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#8
Is it possible that faulty BCM is somehow causing the remaining 120mA draw even when the fuse is pulled out?
Yes, and it was why I asked to have you look for a drain - even at the alternators main post - to try and localize the drain.

The BCM seems to be the culprit and yes, the BCM monitors other areas and it is supposed to be able to shut down the entire system for it was designed as a "passthru" for the power flow and it being able to control not just the flash rate of the turn signal - but the regulator back at the alternator to make sure the voltages even to the extreme lengths of wire routed to the exterior bulbs and the connections to them, are getting enough power and it's regulated well enough to extend the life of the bulbs versus the once given approach of your car maintenance - it's your responsibility if the brake light bulb burned out - it can tell you that - that is the "fingers" it has in many of the sub-systems that car has.

There are many loops in the wires that make the BCM such a mess, because it has the run power to the part, then have a wire run back to report to the BCM about it. - or in some instances the LIN network can pulse a signal and have the devices report their status and save wiring hassles that way.

To simply "blame the BCM" seems to be a bit blunt but at the moment and unless there's a light the BCM is not able to control because it was installed after the car was built at Ford - it is the only way to know truly if it was at fault - is to replace or swap it with another one - and you're correct. It's not easy nor fun tearing apart a dashboard just to install and test a module.
 

Handy Andy

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#9
Just to ask, the 120mA seems like a lamp like a 168 or even a 194 bulb, is still lit in some fashion.

What is your Trim level on the car?

(Thinking a valet Glove box or even a Visor light is being turned on and left on)

Now, the part about the battery from earlier - we oftentimes ask that you clean up the battery terminals and also those battery power connection points like Ground and the connections in that little Red cover on the battery that houses the "breakout" box for sub systems like EPAS, Main and any other extensions like Audio and Lights - so if the trim level is above - say, an SE, then the extra lighting might be what is causing this. Something might be getting left on and no one knows where or how.
 


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