By on May 19, 2016

2011 Lincoln MKZ Hybrid

TTAC commentator claytori writes:

Hello Sajeev,

This email is about my 80-year-old mother-in-law Shirley, who is a sweetie and thinks I can fix anything. I hit the MIL jackpot.

Shirley owns a 2010 Lincoln MKZ 3.5 V6 with about 35,000 miles on it. About a year ago, the battery died on the Lincoln. CAA replaced it with another battery with a 13-month replacement warranty, on which less than 1 week remains.

Two weeks ago, the car wouldn’t start again, so I boosted it from my Saab 9-3, which sits beside the Lincoln in a heated garage. It started right away. As she doesn’t drive it more than about 3 miles at a time, I drove the car for a day to charge up the battery.

The battery was great for two days — then dead again.

I drove the Lincoln to work after another boost and did some parasitic drain diagnosis. There’s a 2A drain from a 120A fuse on the battery post feeding a wire that goes to the “smart” fuse panel. That panel is thoroughly buried behind the instrument panel. I subscribed to Alldata for the electrical schematics and found out the panel has some microprocessor parts, MOSFETs, and other miscellaneous bits.

Since it must be divorced and married to the car’s computer network for proper replacement, I condemned the Lincoln to the dealer. The techs said they couldn’t find a problem, and called Shirley to pick up the car. When she went to start the car to head home from the dealer, the MKZ was dead. She’s understandably very upset.

The dealer wants to replace a perfectly good battery because the techs are too lazy or incompetent to do a proper investigation. The battery is as fine as you’d expect after being drawn down a few times. The alternator is also fine. I don’t know what to tell her after this.

I’d fix the issue myself, but one of the four cables connected to the panel won’t allow it to come down, as it’s held with a plastic clip. Do I just pull hard and break the clip? Do I tell her to leave the car at the dealer until the mechanics get tired of looking at it and actually fix it?

Shirley won’t take cabs as she thinks the drivers are all robbers, rapists, terrorists, or a combination of all three, nor will she drive our spare car.

Sajeev answers:

Your mother-in-law is right about you: I admire your masterful diagnostic work.

From what I see on the Ford Fusion forums, either break the clip or remove the driver’s seat (mind the airbag!) for access without turning your back into a pretzel. I’d break the clip and be done with it, but that’s your call.

After you complete the diagnosis, let’s hope you don’t have to replace the smart junction box. I reckon you’re pulling out the driver’s seat for better access on that job.

[Image: Lincoln]

Send your queries to [email protected]. Spare no details and ask for a speedy resolution if you’re in a hurry…but be realistic, and use your make/model specific forums instead of TTAC for more timely advice.

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43 Comments on “Piston Slap: Why You So Stupid, Smart Junction Box?!...”

  • avatar

    I don’t have the same faith you do with the battery. I would replace it, especially since you only have a few days left on the replacement warranty.

    As for the draw, I probably wouldn’t suspect the fuse panel right away. If something is staying awake, it will be getting it’s power through the panel. To properly check for a draw, you will need to latch all the doors, and lock the car. Allow it to go to sleep. With an ammeter inline with the ground post of the battery wait and hour or so. Your draw should be under .040 amps. Let it sit overnight while the meter monitors the draw. Check the min/max on the meter to see if there were any spikes overnight.

  • avatar


    • 0 avatar

      Who on earth buys a new car battery with a 13 month warranty?

      • 0 avatar

        They’ll sell you a 100 month warranty if you want, but you’ll just pay a lot more for the same battery. Except they know most won’t have car after a couple years or lose the receipt.

        I buy the $39, “90 day” new/rebuilt batteries and get about 36 months out of them. They’re just as good or better than the Diehard/Energizer/Interstate/etc, that I only get a couple years out of.

        • 0 avatar

          I put Optima batteries in all my cars. I pay $180 once and never worry about them again. When I get rid of the car I take the battery back out and move it to the next car.

          That said, this isn’t a battery issue. His diagnosis shows it. A 2a draw will easily drain a battery in two days.

  • avatar

    replace the batt is the easy short tern solution, if your sure it is the not the correct answer I would call the lincoln dealer and find the service manager and have them fix the damm car, after all should not Lincoln be about service?

  • avatar

    Over the years I’ve had three batteries fail before or at one year. That said, the battery was most likely killed by some electrical problem.

  • avatar

    I have an older (1999) Ford vehicle that made me aware of its “smart junction box”-type system for control of everything electronic except for serious stuff like head/brake lights, horn, etc. The GEM module drove me nuts – the heater fan would start up in the middle of the night and drain the battery. Then the interior lights would come on and off at will draining the battery. Then the a/c compressor would engage regardless of heater switch setting. I found that condensation was dripping onto it causing it to loose its mind. It is somewhat corroded after 17 years but I’m not going to pay the $500 or so to replace it (and have it reprogrammed for my truck). I’ll just leave the interior light relay and fuse pulled and go on with life. GM has the same thing; our ’98 Yukon has magic interior lighting and door locks due to these crazy modules which, of course, also drain the battery.

  • avatar

    If it’s still warranty, dump its contents and fill with tap water. Otherwise they may charge it, test it, and say it’s still good.

  • avatar

    If the battery was provided by CAA I wouldn’t be surprised if it were older stock and/or discharged too long for a full service life.

  • avatar

    “She does not drive it for more than 3 miles at a time”…

    There is your clue. MBella is correct that there is a time down for much of the electronics. Not sure if the appropriate wait period was given prior to trouble shooting. The module may check out just fine. If it does I suspect that such a usage pattern of minimal driving will, over time, allow the battery to deplete. Sounds like you are in Canada (CAA)so you also had a winter of cold to exacerbate the problem – it is not always in the heated garage when she uses it. This is not as unusual as you might think. I occasionally put my elderly father’s Avalon on a charger because of slow cranks at startup and flickering lights. High cycle, low distance driving is murder on cars.

  • avatar

    If this was a BMW, they would recommend replacing the battery and then using a battery tender or driving it more than a few miles at a time and more frequently. This has been a common complaint with BMW’s for at least 10 years. When the battery gets low, some modules misbehave and don’t go to sleep. Some modules stay awake for a period of time after the car is turned off, and shouldn’t have a negative effect on a good battery and frequently driven car.

    The Lincoln may be the same. There are a lot of systems running even when the car is off, just waiting for you to walk within sensor range so it can turn on the lights and prepare for your driving experience.

    • 0 avatar
      Kyree S. Williams

      Never mind that BMWs use expensive-ass absorbent glass matt batteries that have to be programmed to the cars, and that cars with the N63 (4.4-liter twin-turbo V8) actually do eat batteries excessively because of the dynamic charging system. Between that and the N63’s apparent thirst for oil, BMW’s genius solution was to shorten the maintenance intervals.

    • 0 avatar

      Trickle charger or a larger solar charger FTW, yes.

  • avatar

    What the heck is a smart junction box? Every junction box I deal with is a box where wires connect via screw down terminals. Whenever there is a draw, 9 times out of 10, its because there is a ground in the box.

    • 0 avatar

      A “smart junction box” is part of the car’s distributed computing system. There is a processor in there somewhere turning stuff on/off depending on operating conditions, function calls from other processors in the car, and phases of the moon.

    • 0 avatar

      the “smart junction box” is a combination of the interior power distribution box/fuse panel and a couple of other modules, e.g. the body control module (BCM) and wireless key transceiver.

      • 0 avatar
        Kyree S. Williams

        Is the smart junction box the same module that decides which systems to prioritize in the case of a power fault (disabling the power seats or the radio instead of the instrument panel)?

      • 0 avatar

        Presumably replacing a bunch of physical relays, too.

        (Thus the MOSFETs, which are used for high-power switching.

        I mean, you can use them as analog amplifiers, but that makes no sense in this context, and “as a solid-state relay replacement” does.)

  • avatar

    Plug to battery maintener like optimate6 all the time in garage will help after a new battery replacement.

  • avatar

    Buy a fresh, glass mat, deep discharge battery (about $250 USD) and sleep happily thereafter.
    Welcome to the 21st century where customer service means that after begging, pleading and threatening they actually repair something you’ve already paid for.

    • 0 avatar

      That’s not going to help that much, as you can’t get the battery fully charged during short-trip driving. No matter how exotic the battery is.

      The battery maintainer is the solution, and you don’t need a $250 battery then – just the regular $95 Interstate one available from Costco.

  • avatar

    Can you move the draining circuit to another that’s switched to ACC on?

  • avatar

    I have found that simply jumping a battery that has been drained more than once and driving around for a little while is not enough to fully recharge it. I think you would need to drive non-stop for over an hour. I recently had a battery in a little-used car that I was ready to just replace because it wasn’t holding a charge, but a complimentary slow charge from Autozone did the trick and it’s been fine ever since.

    • 0 avatar

      This. My LS460 often sits two or even three weeks without being driven, and on a couple of occasions the battery has drained during that time. The first time, I knew the battery was on its way out, but didn’t have time to replace it immediately. I jumped it from my Legend, drove for an hour, and it died again the next day. After that, I drove the car every day for a week, and the battery was healthy enough after the everyday driving to last until I could do the replacement.

      The next drain was thanks to a bum battery $CheapPartsStore sold me, probably old stock; that’s a different story…

  • avatar

    “There’s a 2A drain from a 120A fuse on the battery post feeding a wire that goes to the “smart” fuse panel.”


  • avatar

    Would she be averse to plugging / unplugging a hardwired battery tender when she leaves / gets home? Heck, even if you plugged it in overnight and unplugged it before you left for the day, that should at least give the battery more of a fighting chance. I learned this the hard way with a Touareg that was infrequently driven. Once you get a low voltage condition you really need to disconnect the battery altogether, cycle the key to drain any residual voltage, connect a fully charged good battery, and then clear all codes. Another thing to remember is that a parts store (and maybe even dealership) battery tester doesn’t draw enough amperage (only about 50/100) to properly test a marginal battery. The Touareg had a “good” battery that wouldn’t start it without a jump, and I checked all the connections and resistances. You’re better off measuring cranking voltage in the car, or using a carbon pile 500A tester.
    Good luck.

  • avatar

    Just wanted to echo the above poster regarding BMW. Are you sure there is an actual problem with the Lincoln? The fact the car is rarely driven then when it is it is not enough to fully charged the battery makes me think that’s the problem and the car just always has some natural drain

    My grandfather has had 2-3 BMWs now that he leaves in the garage while he goes to Florida for the winter. All of them end up with dead batteries when he gets back unless he unplugs the battery. Or I think he said there may now be a setting in the idrive for long storage to help prevent it. Anyway, it’s normal. So wondering if Lincoln is similar.

    I’d also just replace the battery, personally. Quick and cheap and if you do it 1x a year or whatever just look at it at maintenance cost and be done.

  • avatar

    Get the battery checked and warrantied if possible. Completely draining a battery multiple times is a great way to kill an already marginal battery. Or turn it into a marginal battery.

    Had this happen to me with a pharisaic drain on my wife’s CR-V. It would randomly have a drain and kill the battery. Finally, after much checking with my DVOM, I figured out that the door close switch was draining the battery. When the vehicle was shut off, something in the computer was sensing that the door was open(circuit was not completed). If the door was opened and closed, the switch would monetarily complete the circuit and shut off the drain from the computer, even though the switch was still open.

    Drove me nuts until I figured it out, that coupled with the battery failing from all the times it was fully discharged.

  • avatar

    As mentioned batteries that have gone really low (below 10.5 volts) have a limited life span left so I would try to get the battery replaced first. Then you need to test it as Mbella laid out and go from there. with lots of 3 mile trips on a electronics heavy car you may have problems in general.

  • avatar

    I’d let the dealer replace the battery then get a charger for it.

  • avatar

    A perfect illustration of stupidity.

    If the dealer is incompetent, find another one to work on the vehicle. All dealers are not lazy – I found out that one lazy Ford dealer does not mean all are. I ditched a lazy one for one that is superbly competent and gifted at finding the root cause and exercising demons on the first attempt.

    Once again divorce the old dealer and find a new one.

    You are an idiot if you keep expecting incompetent PEOPLE to suddenly give a flying monkey’s bum. It shouldn’t have to be this way, but life sucks. Continuing to do the same thing and expecting different results means you are insane and stupid.

  • avatar

    They make batteries with a 13 month warranty? I reread that – no wonder it is being killed.

  • avatar

    My mother has an ’02 (or so) Cadillac that ran fine for the time she and her husband were together. As he passed away not quite a year ago, the Caddy needed a jump start more than once in order for her to go out and do essential business. What I’ve done is told her to start the car no less than once per week and let it run for no less than fifteen minutes each time. More, if at all possible take it out of the driveway and drive around one or two local neighborhoods and farther to actually put some miles under the wheels while she’s at it. Since then it hasn’t needed to be jumped any more but she still barely puts even five miles on it in any given week; usually less.

    To give you an idea of how much the two of them drove together, I ‘inherited’ his ’97 Ford Ranger with less than 20K miles on the clock.

  • avatar
    DC Bruce

    Lead/acid batteries self discharge, so if you put one on the shelf, it will eventually die even if nothing is connected to it. Every car today uses some battery juice when the car is parked–even for something as mundane as the alarm system. It may be that the OP’s measured 2 amp draw is normal. A 30-minute drive will not fully charge a discharged battery, because as the battery voltage rises back to normal, the amount of current delivered to the battery falls off. Cycling the battery between fully discharged and partially charged is a great way to kill it.
    So before ripping out black boxes and so on, the OP’s M-I-L may have to change her driving habits or invest in a low-amp charger and be willing to connect/disconnect it when using the vehicle. Perhaps her clever son in law can figure out a simple plug/unplug way to do it, like the engine block heater pigtail lurking behind the grill of many frozen north vehicles.
    As an aside, this usage profile would be ideal for an EV.

    • 0 avatar

      This was a nice explanation, by the way. And I agree – she sounds like a perfect LEAF customer.

      • 0 avatar

        Sounds like she could even get by with a used Leaf with a depleted battery. Should be able to pick up something like that pretty cheap.

        One nice thing about my Leaf is that when I head to the opposite coast, even if I’m gone for more than a month, it’s perfectly fine. I leave it plugged in so there’s no depletion. No issues from low mileage and sitting long periods like you can get with an ICE. I even have the built-in solar panel to keep the 12-volt system charged, so it would probably be okay parked in an airport lot unplugged.

    • 0 avatar

      There’s no way that a constant 2A drain is normal. Period.

  • avatar

    My 450SL has the same problem. I have gone through every damn possible drain scenario to no avail. We only drive it about 2000 miles per year. But , after yet another dead battery, trust my dear wife to sum it up succinctly. “What does a battery cost-$100? $100 divided by 18 months equals $6 per month – what are you complaining about”? I shut up.

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