Diagnostic_Process_Guide - 6

PLANNING AND EXECUTION

How to establish a
step-by-step diagnostic process
Implementing a formal process not only improves consistency
in the shop but offers many benefits to clients as well.
by Barry Hoyland, Contributing Editor

ost technicians think the
beginning of a diagnostic
process involves breaking
out the scan tool, but that's not
always the case. In order to build a
good diagnostic strategy that will
work on every vehicle with any type
of problem that comes into the shop,
you will need to create a process that
includes using the right tools, and
also one that incorporates obtaining
relevant information.
A good diagnostic process will:
* Improve profits
* Create more consistency from all
technicians
* Make it easier to explain to your
client why you are charging for
diagnosis
* Reduce come backs
* Mis-diagnose fewer vehicles
I have numerous examples throughout my many years in this industry of why
a process is beneficial, but I will give you
a few that stick out and have made a significant impact as to how we approach
any diagnostic process in our shop.

EXAMPLE 1 - ALWAYS DUPLICATE
THE CUSTOMER'S CONCERN
Many years ago, I had a customer bring
in a Pontiac that she stated stalled when
coming to a stop. She left the vehicle with
us along with the spare keys. We checked
the vehicle over and found it had a very
rough idle. The tune-up parts were okay,
but the carburetor mixture could not be
adjusted to clear up the rough idle. We

6 I Diagnostic Process I December 2020

recommended a carburetor overhaul, after
which the car drove fine.
The next day after the customer
picked up the car, she called and stated
she had the same problem when she went
to work that day. We thought that we may
need to adjust the choke, so we had her
bring it back in and leave it overnight. The
next day, we made a minor adjustment
and didn't experience the issue.
The customer picked up the vehicle
and was gone no longer than five minutes when she returned again to complain
about the car stalling. This is when I
decided to go for a ride with her. The first
thing I noticed when I got in the passenger
side was that she had exchanged the key
ring she left us, which only had two keys
on it, with one that had a long tether with
at least 20 keys and gadgets on it.
She left the lot and, as I expected, the
weight of all those keys swung forward
when she stopped and shut off the ignition. After that moment we made sure
that step one of every diagnosis is to
duplicate the customer's concern, even
if they need to drive the car.
Hand in hand with duplicating the
problem is asking enough of the right
questions to make sure you have enough
information to duplicate the issue.
We had another customer that complained of a noise when driving on the
freeway. We drove the car and found no
unusual noises. We asked the driver to
take us for a ride and found that when
the car was driven at approximately 75
mph (15 mph over our speed limit) there

was a wind noise that occurred, which
turned out to be air crossing over the roof
rack. Since we don't drive vehicles over
the speed limit, we were unable to duplicate the noise.

EXAMPLE 2 - ALWAYS
CHECK THE BASICS
I had a very good diagnostic technician
that I relied on to perform most of our
emissions and drivability issues. In almost
every case, he would diagnose the issue
quickly and correctly, but one day he made
an error which highlighted some missteps
in our diagnostic routine. In short, we did
not have a process where every technician
used the same steps on every vehicle and
followed a set of tests that checked all of
the basic mechanical and electrical standards each vehicle must meet.
Every vehicle needs a good battery
and charging system in order for all the
electrical components to function. Every
vehicle needs a mechanically sound
engine in order for the computer to function properly. If the engine's mechanical
functions are compromised in any way,
the computer can't do anything to correct it.
My technician made a very common
error: he didn't check the basics at the
beginning of his process. In this case, my
technician was tasked with diagnosing a
check engine light. This car, a Mustang,
had a code for a faulty manifold absolute pressure (MAP) sensor. My technician replaced the sensor, then came to me
stating that the new sensor was defective

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