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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 effective.

Initial inspection

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 correctly:

  1. Body
    1. Damage to any of the panels, latches, lights, mirrors, and glass.
  2. Chassis
    1. Look for any scrapes, or bent components that indicate a major impact.
  3. Fluid Leaks
    1. Look under the vehicle for any puddles or stains on the pavement.
  4. Tires
    1. Inspect the sidewall for bubbles, cuts, and gouges. The tread for exposed cords, or severe cupping.
  5. Aftermarket Items
    1. Wheels and tires (size and offset can affect drivability).
    2. Anything mounted to the factory paneling, or framework.
    3. 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 PCM signals.

*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 mistake”.

Road Test

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:

  1. Happens cold or hot. Electrical issues or internal cross leaks are usually affected by temperature changes.
  2. Happens under heavy accel or cornering. This would likely be a low fluid level (see previous article on fluid levels).
  3. Happens under light throttle. This may be high pressure, possibly from loss of pressure control.

This information paints a picture for you and helps narrow down your diagnosis.

Visual inspection

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.

Here’s what to look for:

  1. Check visually, all main power cables and their connections. They should be free of physical damage and corrosion.
  2. Perform a wiggle test on the cables, looking for loose connections.
  3. Look for missing components (connectors or cables that are not plugged in or free hanging).
  4. Watch for hoses or cables that are pinched or pulled tight, indicating they are not routed correctly.
  5. Look for anything bent or worn such as axle shafts or mounts.
  6. 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.

Case study

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.

Case study

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 future.


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.