Recently a friend had his Mazda 3 serviced at an independent mechanic
and when he paid the bill he observed a charge for connecting a scanner
to the car. He thought that was a rip off but he did note that the bill
made mention of a couple of impending issues, the most notable being the
battery identified as sub-par. He said it was always starting the car
Ok. I spent some time telling him that you don’t connect a scanner just
to look for fault codes. It’s quite valid to look at the Parameter
Identification Data (PID) values as well. Looking at the PIDs will tell
you, if you’re familiar with the vehicle, what is deteriorating and what
is unchanged. One of the components identified as potentially failing
was the battery and, as I have said in the past, batteries rarely fail
without warning. They usually give indications of imminent failure long
before the actual failure occurs since batteries degrade over time. You
just need to be sensitive to *changes* in normal operations. In my
case, I was sensitive to changes in *engine cranking* and replaced the
battery in my previous Toy *before* it died. Before it even *flagged* a
battery issue in fact.
I put my scan tool on the Mazda 3 (with start/stop bullshit fitted) and,
sure enough, it too showed the battery was deteriorating. Friend
replaced the battery, since it was his daughter’s car driven daily to
Grafton and/or Tweed Heads, and all OBD2 issues went away. The Mazda 3,
with its Start/Stop technology, tends to be hard on batteries anyway. So
where does the EMS get its battery condition information from anyway?
From one of these;

https://www.samarins.com/glossary/battery-sensor.html

Many modern cars have a battery current sensor. It might
also be called a battery management or monitor sensor, or
simply a battery sensor. Often, it is installed on the negative
battery terminal or on the cable. In some cars, it might be
installed on the positive terminal. Some cars have two
battery sensors, one on each terminal.
How the battery sensor works: it measures the current to
and from the battery. The sensor may also monitor the
voltage, state of charge and state of health of the battery
(aging). In some cars, it even measures the temperature of
the battery. The vehicle computer (BCM or PCM) uses
these inputs to precisely adjust charging system voltage,
idle speed and other parameters for better fuel efficiency
and longer battery life. This system is called Power or
Battery Management System or BMS. If the system
detects that the battery is getting weak, it may turn off
some electrical accessories (load shedding), such as the
navigation, heated steering, heated seats, etc., to save
the battery power. In this case, the computer will display
a warning message on the instrument panel.
The function of the battery sensor is particularly
important in vehicles with Stop-Start feature, as the
battery management system must verify that the battery
has enough charge to re-start the vehicle. If the battery is
low on charge, the Stop-Start feature is disabled. The
charging system current is also often higher in vehicles
with Stop-Start feature. For this reason, in some vehicles,
if the sensor has been disconnected or the battery has
been replaced, the Stop-Start feature might not work for
some time, until the computer (BCM or PCM) re-learns
the parameters of the battery.

Very useful little jiggers and the information they generate is used by
the intelligent charging system. IOW, they are involved in the process
of checking the state of charge of the battery and in managing the
charging process. My Toy has one, looks a little different but similar
functionality. What’s more, they connect to the CAN bus and can be
interrogated by the scan tool, very convenient for *preventative
maintenance*, especially considering that batteries, like tyres, are
considered *consumerables* with a finite lifespan. So, essentially, we
have a sensor that monitors and manages a consumerable that is
*critical* to the effective operation of OBD2 systems.
The point I am making, however, is not so much about batteries per se
but checking of the vehicle at regular service intervals with a
scantool. Though people may whinge about the cost dealers and Indies
impose at service intervals for connecting a scan tool and reading
vehicle data, the idea is valid. For one, most scan tools require a
subscription in order to maintain their currency and, for the
professional units, that subscription can be in the thousands of dollars
annually. The dealers and Indies need to recover this cost from the
customer base. After all, it was once considered normal to connect up a
dwell meter to check points gaps during a service. The other is that
scan tools can reveal much more than just DTCs. A benefit of the OBD2
system is ability to poll the system to read real time data from the
sensors and the calculations made by the EMS. Under the established
standards of the OBD2 system, a common set of values is shared among all
vehicle manufacturers. These data sets are known as PIDs, or Parameter
Identification Data, and these allow the mechanic to view the
information from the sensors and the EMS in real time. The mechanic
looks for possible invalid data or clues about the running conditions of
the vehicle. By looking at the PIDs every service interval, the mechanic
can see if the values are in their happy place, trending away, or are
getting close to parameter limits. Remember, if a parameter *exceeds*
the limits, that will usually generate some form of DTC. A good example
is the LTFT, an EMS generated value. The parameter limits are,
typically, 10% before a DTC is generated and the MIL lit but on some
vehicles can be as much as 25%. That’s a heck of a lot of leeway. The
technician can run further checks if the LTFT value is getting a tad
high. If it is, that indicates potential future issues with other
components such as O2 sensors, air leaks and more. If you have a scan
tool that can save OBD2 PIDs, they can be downloaded to a printer for a
hard copy record of vehicle conditions at every service. That hard copy
record can be a valuable resource when current PID values are no longer
in their happy place.

I have been regularly connecting up my scan tool to the Toy at regular
intervals and keeping tabs on the PID values so I have a fairly good
idea of what *normal* is for the PIDs even though I haven’t been saving
the data collected. It has to be said though that PID values are
something that a tech needs to be very familiar with in order to discern
divergent values. That requires a fair degree of experience with the
particular vehicle marques one regularly works on and the best way to
gain such experience is to plug a scantool in at every service - you
know what the current status is, what the norm is for that vehicle, and
whether it is divergent from the norm. If you've printed the PID data
each time, you'll have a running record which can be invaluable at fault
diagnosis time.

So, in summary, connecting a scantool should be considered an invaluable
part of every service and provides the opportunity for the PIDs to be
inspected to determine the current and future health of the vehicle.

More anon

--
Xeno

Nothing astonishes Noddy so much as common sense and plain dealing.
(with apologies to Ralph Waldo Emerson)