12volt battery and HVB Observations

[Matt Zach]

New forum member.  Bought a 2014 MKZ Hybrid in Nov 2019 with 94.5K miles, now has 104.5K miles.  Three weeks ago the 12volt battery died.  Luckily the car was unlocked.  Popped the hood and tested the voltage at the jump starting bolts and it read 2.5 volts (yes, two point five volts).  Trunk would not open with buttons or fobs, so put down the back seats, crawled back a bit into trunk and pulled the emergency release.  Voltage at the 12volt in the trunk was 2.5 volts.  Bought the new specified 12volt Motorcraft battery at the Ford dealer and installed that in trunk.  Car now started and ran fine, but trunk would not fully close, nor open automatically.  Bought the new Rear Gate Trunk Module (RGTM) from a Ford dealer and installed that ( online videos have been very helpful with this process!).  Trunk now locks and cinches down, and unlocks.  The RGTM should be reprogrammed with updated codes, but dealer would not do this as I installed module myself.  That's OK, I can live with some reduced functionality, but I still had a problem with finding parasitic electric draws.  Car 12volt battery was not charging properly, battery voltage would drop overnight to low 12 range.   Did a lot of web searching and reading, including in this forum and the Ford Fusion Hybrid forum.

 

I have 3 different OBD2 readers (cheap, Autel MK808, and Forscan).  I have used all three to check and turn off DTC codes, and see into as many relevant systems as I could.  I have used Forscan to turn off as many nonessential electric draws as I could, to test/set a new battery "type", and to test/observe results with BMS on and BMS off.  

 

One observation I have from this project is that the 12volt battery can and does get charged from the HVB.  One way to see this is to pop open the hood and check the voltage (with multimeter) with car totally off, then turn on the car BUT don't start it (push the start button without your foot on the brake).  With car totally "off" I had readings of 12.2+ volts, but with KOEO (key on engine off) I had readings 14.2+ volts.  (Some of the cars many systems start drawing electricity when you open the car door, and it takes a while - minutes - for them to go back to sleep after your shut the car door.)  This makes sense to me.  The gas engine can power the car and charge the HVB.  The HVB is getting about 300+ volts from the engine's generator.  The HVB assembly includes a DC to DC inverter that steps down the HVB voltage to the 14+ range for the 12 volt battery.  This is what I think is going on, in very simplified terms.

 

At present, with the reduction in interior lights and other nonessential draws, and with BMS off, I finally had the 12volt battery up to 12.8 volts after a long afternoon drive yesterday and it settled down to 12.6 volts overnight - which is right where I want it to be.

 

Matt

 

 

[sandsmccoy]

We purchased my wife's 2015 MKZ Hybrid in early 2016 and absolutely love the car with one exception - it has stranded us on numerous occasions.  It does this randomly - no problems for many months and then when you least expect it - a dead battery (totally drained).  We took the car while under warranty to several dealers on several occasions and of course, they couldn't duplicate the problem.  We have replaced the 12 volt battery 3 times (twice at the dealers' expense, 1 at mine).  We now carry an older portable battery supply (new automatic - microprocessor controlled) jumper systems only work if your battery has at least a partial charge) so at least we aren't stranded anymore when this happens (although its a pain to get into the trunk without any power).    What's unusual about this is as soon as I connect my portable battery supply to the jumper points under the hood and start the car, immediately disconnect the portable battery supply and shutoff the car, I have enough voltage in the battery to hook my automatic battery charger and fully charge the battery.  In my experience 12 volt batteries don't charge this fast, although I suppose the hybrid battery could possibly be a factor.  This would seem to me to be a software glitch of some kind but who knows - apparently Lincoln service centers do not.  I am going to start documenting our problems by checking the status of the 12 volt battery on a regular basis to see if I can figure out what is causing this problem.  I'll post any results I find to this thread in the future.

[Mcondo]

Any problems with the multiple trunk open or closing mechanisms? I experienced a drained battery and it was the trunk module. Biggest tell - with trunk open, inner deck lid button to close trunk didn't work. 

[Matt Zach]

sandsmccoy--  I replaced with the official battery, and now for 726-04-01 I use 1000  001E  0969.  BMS is turned off at xxXX xxxx xxxx, with the 00 values.

 

I see charging voltage 14.2-14.5 volts (with BMS on I was seeing 14.8-15.0 volts - very odd), and 12.8-13.0 when I turn off the car, and 12.5-12.6 the next morning.

I set the power point (old cigarette lighter socket) to stay on for 18 hours and I can look in the window at the plug in voltage meter (which can also recharge usb power devices) and see the current voltage.  Note if you open a door system power up and you won't get an accurate reading.  Standing by the car with fob in your pocket will probably also turn on some systems.  I bought the plug in voltage meter/charger online for about $15.00

 

I changed 726-39-01 from 1194 0101 000E   to   FD20  0101  0086  to get the PP to stay on for 18 hrs

 

 

[Matt Zach]

Mcondo-- With my new RGTM (rear gate trunk module) the trunk locks and unlocks but does not power open or power closed.  I have to do that manually, but that's a small price for me to pay to have the car reliably unlock and start in the morning .  I have been leaving the car unlocked overnight in my driveway, with a spare 12volt and jumper cables just in case....

 

I did have trunk power open and close issues in the weeks before the fail, including inner button not working.

 

So you got a new RGTM.  Dealer installed and flashed with the new official codes/software?  Have you been monitoring your battery voltage since the new RGTM?

Any data you can post?

[Matt Zach]

sandsmccoy--  I replaced with the official battery, and now for 726-04-01 I use 1000  001E  0969.  BMS is turned off at xxXX xxxx xxxx, with the 00 values.

 

I see charging voltage 14.2-14.5 volts (with BMS on I was seeing 14.8-15.0 volts - very odd), and 12.8-13.0 when I turn off the car, and 12.5-12.6 the next morning.

I set the power point (old cigarette lighter socket) to stay on for 18 hours and I can look in the window at the plug in voltage meter (which can also recharge usb power devices) and see the current voltage.  Note if you open a door system power up and you won't get an accurate reading.  Standing by the car with fob in your pocket will probably also turn on some systems.  I bought the plug in voltage meter/charger online for about $15.00

 

I changed 726-39-01 from 1194 0101 000E   to   FD20  0101  0086  to get the PP to stay on for 18 hrs

 

 

Sorry --- I should have specified that I used Forscan to rewrite those codes.  It is not really user friendly, but there is a lot online to help new users, and the 2 edits I show above are pretty straightforward after spending some time learning how to use it.  Software cost is $10.00 for a yrs license.