From: xenolith@optusnet.com.au
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.
--
Xeno
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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