Back to basics — Automotive diagnosis isn't always a high-tech issue

Have you ever gone to the doctor for a specific complaint and yet the first thing they do is check your heart, lungs, blood pressure, eyes, nose, and reflexes, before getting to the problem that brought you there in the first place? Well, the doctor is checking the basics before focusing on the complaint to get an idea of your overall health.

I think we can relate to this when it comes to repairs, too. A simple example is putting a new set of tires on a car that is completely shot. I now understand why a doctor checks all the basics to see if something else might seem to be the problem. With all those diagnostic checks, the doctor is evaluating your overall health to see if your body is worth installing any new parts. So, this brings me to my next question: Do we check the basics during our diagnostic workflow?

Have you worked on an electrical issue for a full eight-hour day, only to discover a blown fuse? I have. How can you charge a customer for that time? You can’t, and thank goodness. In my early career, flat-rate pay was standard, so no one was hurt. But I made it up to the customer by working longer hours and through many lunches. As hard as the lessons I learned, they made me a better diagnostic technician. The “basics” have been important ever since.

I started in the business in the 70s and 80s, pre-OBD. The automotive engine basics were spark, fuel, and compression. I always started with our senses. First, a listen and look approach to spot problems. Next, I added the smell inspection. I know you all have smelled a rich mixture or a failing catalytic converter. Next is touch. Any vibrations? Temperature differences? The fifth sense is taste. I have only used that in diagnostics by accident. I would not recommend it.

When I had an engine misfire, the first thing I did, if I didn’t catch anything for ignition or fuel problems, was a vacuum test with an analog gauge. It gave me a good idea of the engine’s mechanical health. A steady needle between 18" to 20" of vacuum indicated a healthy engine.

No need for a time-consuming compression test. A good vacuum told me to look for a miss elsewhere. Plus, with my gauge hooked up, I increased the RPMs to 2000+. If the vacuum dropped below the previous idle, I suspected a clogged catalytic converter, which has been installed on cars since 1975. This test is still a great way to verify a cat code today. When I had a SUN machine or Snap-on scope, I performed a secondary ignition or a power balance test to pinpoint the problem. The SUN scope had hydrocarbons (HC) and a carbon monoxide (CO) analyzer that gave a good idea of the air-fuel ratio.

In today’s world, we still need to check basics, especially now that there are even more basics to check that are vital to a vehicle’s computer network.

Here's a more detailed breakdown of basic vehicle testing:

Initial Observation and Symptom Gathering

• Check for warning lights
• Listen for unusual noises, which might indicate a mechanical issue - examples include squealing, grinding, or clicking
• Feel for vibrations or shaking
• Note any fluid leaks

Basic Diagnostic Testing

Use a diagnostic tool to connect to the vehicle's OBD-II adapter to read any stored trouble codes. Note that a Snap-on scanner performs a pre-scan that includes simultaneous code scanning for OBD-II and OEM protocols to ensure a thorough diagnostic read-out.

Furthermore, if you are using a tool that has a Fast-Track troubleshooting workflow, the next step is to check for filtered TSBs that are relevant to the specific code. Moreover, this workflow guides you to commonly replaced parts, on the exact vehicle you are working on, that will correct the code.

Most likely, looking at the data stream is the next step to see if anything is outside of the specification window. The Snap-on filtered Smart Data presents red flags if anything is out of spec.

Additional Testing

You may need to get into functional tests to isolate the problem.

You may not need to check fuses on many circuits. For example, if a power window does not work, use a functional test to command the window up and down. If so, it indicates the fuse is good, as well as the circuit and motor. Next, look at the car window switch. Computer controls allow basic checks faster than ever before.

Furthermore, you can do a compression test. Let's take this Ford Focus as an example, in under a minute.

Repair and Verification

• Repair the identified issues. Based on the diagnostic results and testing, repair or replace any faulty components. 
• Reset or relearn core and related modules to ensure this vehicle does not come back due to the module not recognizing the new component(s).
• Verify the repair. 

Post repair, relearn or reset is complete. Retest the vehicle to ensure that the problem has been resolved. Do a post-scan. In some cases, a test drive would be prudent. Comebacks are profit killers – avoid them at all costs!

I am willing to bet you, like me, have been guilty of not finding a basic, simple issue because we are too busy wading through the high-tech areas looking for that sophisticated problem. We still need to check those fuses, and we can check them a whole lot faster today.

For more on this topic, visit Snap-on's website.