MACS Monthly Newsletter - 2022 - MAY6

You don't need the scan tool, but the alternative raises an issue
When you're facing a job you've done a " million
times, " but never on the specific year-make-model
car in your shop, it 's easy to attack it with a nonchalant
attitude. And when you do, it can turn into
a toughie, both from a standpoint of what it specifically
takes to do and what it takes to finish it successfully.
Here's an example that in one particular
way has been the same for many years. However, the
vehicle itself (a GMC Sierra pickup) is a late model
and there are some nuances on any late model that
can throw you for a loop.
As you know, electronic HVAC actuators have been
with us for a long time, including on most so-called
" manual " A/C systems, and they are a common failure
item. In this case, on the late-model GMC Sierra
pickup, the actuator for outside air failed, and
the aftermarket technician replaced it with a new
(OE) part, reassembled and reinstalled on the HVAC
case and then tried to operate the system. The door
moved but nowhere near full travel. Did he get a defective
part? No,
it just needs to go through a recalibration,
and a technician at the dealership told
him it 's an operation on the scan tool. The independent
garage's technician tried to find it on both of
his (aftermarket) scan tools, but neither one had the
recalibration.
That 's a common enough issue independent technicians
often complain about, because the makers
of aftermarket scan tools can't include every possible
recalibration or similar algorithm in an allmakes
unit. The scan tool makers have to pay licensing
fees for most of the OE software they could
install, so they have to use their best judgment on
what an aftermarket technician will need. And in this
Then reinstall the fuse, start the vehicle and wait
a minimum of 40 seconds, during which the module
should self-calibrate. Finally, make sure that no
trouble codes have just set.
The problem of finding a specific fuse can be a
real-world headache. There's usually more than one
fuse block (box) and the contents may not be clearly
marked. The fuse labeling isn't clear? In addition to
fuse rating, it might even be necessary to confirm a
fuse is what you're looking for by checking the colors
of the wiring insulation (at the fuse holder) to
the wiring diagram. Not necessarily easy to do. v
specific case the decision made very good sense,
because unlike the service diagnostic approach of
OE carmakers in general, General Motors (thoughtfully)
has provided an alternative procedure that
doesn't require any tool at all. This procedure applies
to Chevy pickups as well as GMC, so it has
broad-based application.
You've got to perform the procedure exactly as
prescribed, with everything assembled, including
the actuator, and all trouble codes cleared and the
ignition turned off. The actuator circuit should not
be " tested " with the actuator connected to its wiring,
out of the system. The first step is to remove the
HVAC module fuse for at least 10 seconds, and here
is where many technicians have gone wrong. They
take out the wrong fuse, specifically a 15-amp auxiliary
fuse that is primarily for the rear defogger. The
correct fuse is a 10-amp (Figure 8). Not the technicians'
fault really, as none of the diagrams, including
the OE, are really clear on this point.
May 2022
6
MACS Service Reports
MACS Monthly Newsletter - 2022

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