MACS Monthly Newsletter - 2017 - FEB2

checked the system with a scan tool - and saw a code
for that actuator was logged, which said the diagnostic
logic was apparently functional. But what about a nonelectronic issue? Well, the fact that there's heat to the rear
says the engine cooling system and thermostat are behaving normally. How about the front heater circuit? Let's
check that. No issue detected. In fact there's heat to the
front for a couple of seconds, but then it stops, perhaps
indicating an airflow switching issue (no heater coolant
valve in the circuit).
Operating the dashboard controls didn't produce heat,
so the technician connected his scan tool and was able to
operate the temperature door, and when at the heat end it
did produce high heat, proving there was nothing wrong
with the actuator or door. With no obvious bad connections, that reduced the diagnosis to the module circuit.
Although there was a reflash listed for the module, the
description was not conclusive, the technician did not
have a reflash device (SAE J2534 Pass-Thru device) or
a subscription for reprogramming. So the technician replaced the module, which went through a self-initialization and the system was back to normal. If the technician had a J2534 device, he could have offered the reflash
as a pre-replacement service attempt, and just maybe it
would have worked. Very few replacement modules

will plug and play, and in this case the apparent answer
is that the new module fixed the problem and whatever
that reflash does in the way of HVAC performance improvement (even as a possible repair) will at this point
not be determined.
Unless you have a short-term subscription in effect at
the time the car is in the shop, we admit the "should I or
shouldn't I reflash" is difficult to decide. The typical sub
is $55-$70, and with the time necessary for the job (hookup, service bay tied up, etc.) there is a cost that can run
over $100, not pocket change you want to absorb if the
reflash turns out to be a waste of time. If you have a few
cars in the shop that seemingly will benefit from a reflash,
well then you can amortize the cost to something a customer can accept ("We applied this reflash - description
provided - and although it doesn't seem to have fixed
the problem, it should smooth operation, although a new
actuator also had to be installed. So we're charging only
$65 for the flash.") Or, of course, you simply could just
put the full charge for the reflash on the bill and let it
go at that, without explanation, just the factory service
information's description of the software. But with the
high cost of replacement modules and their even greater
uncertainty for providing a repair, scheduling the vehicle
for a "GM Day" is worth the attempt. ■

REPEAT HEATER CORE FAILURES
The repeat heater core failure issue is one that has been
with us for a long, long time. Shops have tried multiple
grounds with questionable results, and the "I've flushed
the system X number of times" is a line we've all heard.
If the voltmeter test (ground on battery, positive probe
in coolant) produces a reading of 0.4 volt or higher, the
diagnosis of electrolysis makes some sense, although
shops also report that numerical level reading on systems with no heater issues too.
The heaters in Ford products, plus some General Motors models, are the usual targets, but we believe that's
strictly a matter of their high volume in the marketplace.
Here's an example from a 2007 Mitsubishi Galant, and
although the model is an older one, the story is the same.
The replacement heater lasted three weeks; the next
one was leaking two weeks later. The two core replacements were preceded by installation of a radiator several
months earlier.
The condition of the coolant, per a voltmeter test, was
0.4 volt at the first replacement. This spec, as we've indicated, is borderline, and in fact on this particular car,
in a later test was just over 0.5 v at the second, indicating
some amount of corrosion had entered the coolant.
The replacement heater cores were original equipment,
so the possibility of an inferior aftermarket part doesn't
come into the picture. What the shop finally did to fix
the problem does apply: it used a flushing machine on
the system, then went through hoops to drain as much
water from the system as possible, and finally got a volt-

February 2017

meter reading well under 0.4 v. What many shops don't
seem to accept is that even a machine may leave in 20%
of the old coolant, and doing a manual flush can leave in
40% of the old coolant. Disconnecting hoses after even a
machine flush, to get out the water seems like excessive
effort, but unless you know that the water from the tap
is relatively soft, it's good practice. And use of distilled
water to refill gives you an added level of protection.
An alternative is to use a 50-50 mix (anti-freeze and distilled water) to push out the flush and refill the system.
There's some waste of the fresh coolant mixture with this
approach, but when you've replaced a short life heater
core, it's cheap insurance.
Adding grounding straps to the heater core seems to us
as a waste. It's better to ensure the coolant is fresh and to
clean and tighten the OE grounds.
As an aside, we've also been hearing mutterings about
OE heater cores for domestic cars/trucks being sourced
from outside the U.S., and possibly being inferior as a result. Plain fact is that auto parts are sourced worldwide,
and if it's an OE part it meets the same quality control
standards no matter where it's made. Many cars sold
here, even domestic nameplates, as a result will have
heater cores made elsewhere, including the Caribbean
and Central America, China, Thailand, etc. Don't make
assumptions based on country of manufacture.

WHERE'S THE LEAK
The heater core is leaking but from where? Sometimes

MACS Service Reports

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2017