When it comes to speedy diagnosis nothing beats a good visual inspection
and checking the basics. Being a good detective will help you immensely with your diagnosis.
When it’s done correctly and incorporated into your normal routine it can be fast and
When approaching the vehicle walk around the vehicle looking at all 360
degrees. Have a mental checklist to look for, this should be a 1-minute inspection when done
- Damage to any of the panels, latches, lights, mirrors, and glass.
- Look for any scrapes, or bent components that indicate a major impact.
- Fluid Leaks
- Look under the vehicle for any puddles or stains on the pavement.
- Inspect the sidewall for bubbles, cuts, and gouges. The tread for exposed cords, or
- Aftermarket Items
- Wheels and tires (size and offset can affect drivability).
- Anything mounted to the factory paneling, or framework.
- Anything that alters the factory electrical system, snowplows, warning lights,
winches, LED lights, etc.
Aftermarket add-ons could give you the biggest headaches, especially when
they are connected to the vehicle’s electrical system or modify the factory calibration.
When sitting in the vehicle look for anything to indicate the OE
programming was modified, such as a handheld flash tool, Bluetooth Dongle connected to the
DLC, or a mounted device that may be connected to the computer system or sensors to alter
*Note these items may not be the root cause of the issue you are
diagnosing but don’t dismiss it in your troubleshooting. If possible, return the
vehicle to stock during your testing if you suspect it is related to the issue. When
altering OE calibration, it is possible you are diagnosing someone else’s “engineered
With the customer’s complaint and your visual inspection in mind, a proper
road test should be performed if possible. This will serve you well when you’re going
through your diagnosis in the bay. Try several times to repeat a symptom the customer is
describing. See if a pattern develops, for instance, if the transmission has a hard shift
into 2nd gear, try to pinpoint if this:
- Happens cold or hot. Electrical issues or internal cross leaks are usually affected by
- Happens under heavy accel or cornering. This would likely be a low fluid level (see
previous article on fluid levels).
- Happens under light throttle. This may be high pressure, possibly from loss of pressure
This information paints a picture for you and helps narrow down your
How great is it when the customer pays for a 1-hour diagnosis, and when you
put the vehicle on the rack, you find a ground wire that is broken or corroded connection 5
minutes into it? You and the customer will be happy. In their mind, they are thinking the
worst, and it will be very expensive. You’re happy because you made some money and are
moving on to another job. These are the golden nuggets we hope to have daily.
- Check visually, all main power cables and their connections. They should be free of
physical damage and corrosion.
- Perform a wiggle test on the cables, looking for loose connections.
- Look for missing components (connectors or cables that are not plugged in or free
- Watch for hoses or cables that are pinched or pulled tight, indicating they are not
- Look for anything bent or worn such as axle shafts or mounts.
- Look to see if anything was recently taken apart or disturbed.
If recent work was done there may be a tie into why the problem exists. It
is best to thoroughly question the customer about any recent work. Was the vehicle brought
to them because of the problem and they were unable to fix it, or did they get the vehicle
back from them, and then the problem happened? Either way, get a full breakdown of what they
did and list the parts that may have been replaced.
*Don’t trust parts that you didn’t replace either, I would not put my
trust in someone else’s diagnosis, also I’m sure you have heard the saying NEW stands
for Never Ever Worked. That doesn’t mean they are bad parts, just that they haven’t
proven good yet. I have had brand new parts from the dealer that were faulty.
One thing that has been very popular is the addition of aero kits (ground
effects). A vehicle came in with multiple electrical issues including not being able to
shift the car from Park with the key in the “RUN” position. During the initial inspection of
the vehicle, you could clearly see multiple shiny self-tapping screws poorly attaching the
parts to the rocker panels, what caught my attention was where the screws were drilled into.
After removing the plastic panels that cover the wiring harness running under the doors you
could clearly see multiple wires cut and twisted around the screws. Once the wiring was
repaired the issue was cured. This could have taken hours to diagnose if the factory
troubleshooting was done and the obvious was ignored, however, with a good visual inspection
and detective work we were able to diagnose and repair fast and effectively.
Questioning the customer:
It is important to have a detailed service writer that is good at
questioning the customer, and the ability to decipher what the vehicle owner is telling
them. If that is not the case, it may be a good idea to question the vehicle owner yourself.
A customer brought in an older Mustang with a violent shake felt in the
entire vehicle that was present at all times with the engine running. The customer and the
owner of the shop were convinced that the Torque Converter (TC) had lost its balance weights
and the transmission needed to be removed and the TC replaced. After inspecting, and
confirming the weights were in place by looking through the starter hole opening, we began
to isolate what it couldn’t be, so we could narrow down other possibilities. The
issue was engine RPM related, the more RPM the worse the vibration got, it was happening
with the vehicle at a stop and the transmission could be in gear or neutral. We could
eliminate tires, u joints, driveshaft, and transmission (at least from the transmission pump
back) because none of those items were moving when the shake was present. A visual
inspection of the TC and the flex plate was already done, and nothing seemed out of sorts,
so now suspecting an engine-related issue it was time to give the vehicle a second look. It
didn’t take long to see this engine was not the original, it was a fuel injected 5.0l out of
what looked like a late 80’s Mustang, yet the car was a 66 Mustang. This was a breakthrough
in the diagnosis, because if you are familiar with Ford 302 engines you know they switched
the balance weight from 28oz to 50oz in the early 80s when the engine was still carbureted.
Now with this knowledge in hand, we got the customer on the phone and confirmed the
suspicion of the mismatch. The fix was easy as replacing the balancer, it took about an hour
to fix. The customer thought they needed a transmission and torque converter which was about
$3000 in total, when he was presented with a bill of around $500, he was overjoyed. He
eventually spent much more with the shop because he trusted he would be taken care of in the
What are you looking for? The simple answer is don’t overlook or disregard
things you see that are out of place, or suspicious about the vehicle. Don’t be afraid to
question the customer about the history of the vehicle and services. Keep these basic checks
as part of your diagnostic routine. The effort you spend in checking these simple things
will pay you back many times over.