From: Boris@invalid.invalid
Xeno wrote in
news:mk1cp9F9q5gU1@mid.individual.net:
> Boris wrote:
>> My daughter has a 2020 Mazda 3, with about 75k miles. Back on July 2,
>> I wrote about acceleration issues the car was having:
>>
>>
>>
>> A software update seems to have fixed the problem. A new battery was
>> also installed.
>>
>> My daughter is now having more problems with her 2020 Mazda 3.
>>
>> The problem is that every few days the car won't start, and she has to
>> use a charger for about 15 minutes to get it started. She carries the
>> charger with her. Then, it will be fine for a few more days, only to
>> have to repeat the procedure in another few days. Luckily, she's
>> always been at her house or my house where she can plug in the charger.
>
> That is not normal and don’t let anyone tell you it is. To me, it
> sounds like you have a BCM that isn’t going into sleep mode. The BCM,
> when active, consumes between 0.20-0.25 amps. When in sleep mode, it
> should drop to 0.015 amps, IOW, about 15 milliamperes. If the BCM is
> remaining in active mode, it will drop the battery voltage to a level
> where the ECM won’t allow the engine to crank. A BCM that won’t
> enter sleep mode is a sign of a parasitic drain on the battery. You can
> check this by using an ammeter to check the current draw when ignition
> is off and the car is locked. If the current draw remains at 0.20 amps
> or more, you can then test which circuit is faulty by pulling fuses one
> by one and seeing if the current draw drops to sleep mode. Note, only
> have one fuse out at a time. If that shows nothing, you may have a
> faulty BCM. Either way, the car has an issue, its behaviour is not
> normal.
>>
>> She dropped the car off at the dealer's today. I ususally go with her,
>> but I couldn't today. She said the service rep seemed very
>> knowledgeable, but some of the things he told her seemed very odd to
>> me.
>>
>
>
>> 1) He said this is a common problem with newer cars when the owner
>> takes a lot of short trips, and these short trips don't allow the
>> battery time to charge. She does take a lot of short trips, but this
>> seems nuts to me. He sees this a lot with elderly owners who only
>> drive to their nearby store every day, and that it takes about 40
>> minutes of driving to keep a battery charged. Also, on newer cars with
>> all the computerization
>
>> and 'features', the battery is always being drained by something, even
>> when unoccupied. He says this is especially common with Mazdas and
>> Subarus. He suggested using a trickle charger to keep the battery
>> charged.
>>
> Should not need to use a trickle charger if you use the car every few
> days. Even a Toyota Prius will still be able to start the engine after
> *2 months* of no starting. 3 months and the Prius might complain. My
> wife’s Suzuki Swift (2016) sat unused for 6 months and still started
> when I needed to use it. It seems that electricals confuse today’s
> mechanics and electronics confuse them more. Don’t be bluffed by
> bullshit from them. Is it still under factory warranty? If it is,
> they’ll bluff you till it’s expired. Unwanted parasitic draw is a
> problem, the Mazda at the very least needs to have that checked by a
> competent auto electrician who understand the relevant concepts
> involved.
>
> Point to note, the Mazda 3 with the start stop technology requires a
> robust (read:expensive) battery typically of the glass mat type. Don’t
> cheap out on it else you’ll be subject to a litany of subtle issues. A
> cheap battery will give the ECM incorrect (low) voltage readings and the
> ECM will refuse to start the engine. Remember, that button on the dash
> doesn’t start the engine, it only alerts the ECM to the fact that you
> want it to start. If everything checks out to the ECUs satisfaction, inc
> battery voltage, the *ECU* will start the engine. 15 minutes on a small
> charge won’t add much to the battery’s overall charge - but it will
> put a high voltage surface charge into it that will fool the ECM into
> thinking the battery is better than it really is. Remember, the ECM
> checks battery voltage.That’s why it starts after on 15 minutes on
> charge. Check the OEM recommended battery and ensure that it or a direct
> equivalent has been fitted. Just one of the many ways a cheap battery
> can dick you around.
>
> Also note, both the starter and the alternator are under complete
> computer control, ensure those two items are up to snuff. Test the
> alternator under a heavy load, should go to max output. Used to use a
> bank of headlight globes back in the day to provide a load.
>
>> The dealer gave her a loaner, the same model but a 2025. If the above
>> is true, this loaner will also at some point die on her. She's still
>> carrying the charger.
>>
>> 2) Something else he said about newer cars (which has nothing to do
>> with my daughter's car), is that the newer cars get used to how a
>> driver drives, and when another driver gets behind the wheel, the car
>> wants to drive like the first driver is in control. He says a husband
>> and wife will come in saying that the car has a mind of it's own. I
>> can understand a car automatically saving and applying things like seat
>> and mirror positions, and maybe climate control, but...
>>
>> Anyone ever heard of any of the above?
>>
>> Thanks.
>>
> Cars have built in learning ability in engines and transmissions for
> sure. They are adaptive and the driver who drives the car most will
> determine the *style* it adapts to. The more sophisticated cars can
> adapt to multiple drivers and, I presume, they determine the driver from
> the mass applied to the driver’s seat.
>
>
Thanks for the reply.
I spoke with the service rep today, and he assured me that the BCM and ECM
checked out fine, and insisted that the car just isn't driven enough, on a
daily basis, to replenish the battery's charge. I told him that the drive
to bring the car from my daughter's home to his shop was a 50 minute
freeway drive. He said when the battery was tested upon arrival at his
shop, it was only 55% charged, because it was depleted from short trips
and the 50 minute drive was not enough to fully recharge the battery, but
otherwise the battery was good. He said he has many older customers that
also drive very little with the same problem. He tells them to use a
trickle charger.
My daughter's car is a 2020, and the original battery lasted only three
years. The car wouldn't start and the battery wouldn't hold a charge. I
installed a second, appropriate battery in 2023. In July of this year,
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