MACS Service Reports - 2015 - DEC2

technician who fell into this excellent classification basically what they were doing to diagnose vehicles accurately and efficiently. When the survey
was analyzed, the results were amazingly simplistic and consistent amongst the group of successful
diagnostic experts. Those results came together in
a Strategy Based Diagnostics chart (Figure 1) and
a live class by that same name put on at GM training centers throughout the nation. I was fortunate
enough to take the class, which consisted of reviewing the newly created diagnostic chart and then applying it to various vehicles that an instructor had
bugged with a problem. Most technicians who attended this class absolutely loved it. Many felt it
was a tune up of their diagnostic skills, confirming
some methods they already put into practice on a
daily basis, but perhaps had not ever (until taking
the class) put into writing as any particular method. Others who really needed the class quite desperately were not as enthusiastic due to our natural
aversion to change, and in some cases, damaged
egos. A set of test leads came with the class in a
plastic bag that (at the time) fit a variety of popular
GM / Packard terminals to avoid one of the taboos
warned about in the class: improper back probing.

an engine misfire, it's always been and always will
be air, fire and fuel. With HVAC, regardless of what
refrigerant is being used, what runs the compressor
(a belt or electricity), or the strategy of A/C controls that are utilized, the basics remain the same.
Care given to the proper refrigerant charge and refrigerant oil, along with proper airflow and good
power and grounds still apply whether the vehicle
is a 1996 or a 2016 model.
Step 2 is so often overlooked. It requires attention
to details and acute skills of observation. Are aftermarket accessories present? Are there signs of a DoIt-Yourselfer working on the vehicle, such as empty
cans of refrigerant, sealant or dye in the vehicle's
trunk or back seat? Observations like corroded battery cables, worn or slipping drive belt and airflow
restrictions can evade even the best of us if we allow a high tech symptom or DTC to cloud our diagnostic approach to the point where we skip this
important step early on in the game.

Using a Bright Light and Bright Thinking
This step involves as much bright flashlight work
as it does bright thinking work. How many times
have you been told that all the fuses are OK when
indeed one is blown? Incidentally, what is the proper way to check a fuse? Is that a topic too simple
to discuss in a MACS Service Report? I personally
love to zip from fuse point to fuse point (provided
they aren't the type covered with a window) with
a simple 12-volt test light while the ignition and
parking lamps are turned on. That gets just about
everything on the vehicle powered up, and rather
than embark on the Easter egg hunt of finding just
the fuses relevant to the circuits involved in the issue at hand, I check them all. See Figure 2.

SBD Step 1: Verifying Customer Concerns
As the old saying goes, "you can't fix something
that isn't broke." Even intermittent problems can't
be repaired unless we can occasionally replicate
the problem to see it for ourselves. Sometimes the
vehicle's system is performing as designed, and
the customer 's complaint can't be repaired. Step
6 discusses just those scenarios with suggestions
ranging from educating the customer on their vehicle's normal operation to verifying the vehicle is
performing properly with an identical known good
vehicle.

The more complex vehicle
systems get, the easier it is to
fall into the tunnel vision of
believing every problem with
a vehicle is complex. My years
working on a technical hotline
were often spent helping technicians find simple fixes for the
most complicated problems. A
colleague of mine on that hotline always reminded me that
no matter how mind boggling
the vehicle's problem seemed
to be, it always boiled down to
a few basics for each system. For

December 2015

Dave Hobbs

Step 2: Preliminary Checks -
Visual and Operational

Figure 2: Checking all fuses with a test light often works out to be faster than accurately identifying the fuses
in question.

MACS Service Reports

Table of Contents for the Digital Edition of MACS Service Reports - 2015