What is Vehicle Diagnostics?

Tools and procedures during a Vehicle Diagnostic

The word ‘diagnostic’ originates from a Greek word that refers to the capacity or art of distinguishing. In the common sense of understanding, it refers to identifying the nature or cause of something, usually an illness, disorder, or problem. When we talk about vehicle diagnostics, the use of the term is still applicable.

In the past, working on a vehicle was not as computerised as it is nowadays. Mechanics and vehicle owners, who had the knowledge, could diagnose problems and work on these problems with only some basic tools to their disposal. This changed drastically. Due to an immense amount of electronic components, and a sophisticated computer that regulates most of the functions in the vehicle, diagnosing problems and fixing it require a decent amount of knowledge about electronics. Because of this high-tech state, we are not always able to detect the exact cause and location of a problem. This is where the diagnostic tool steps in to save the day!

Today’s diagnostics tools are able to check every aspect of a vehicle, such as the engine control unit (ECU), performance, emissions, oil levels, temperature systems, etc. These diagnostic tools makes the task of diagnosis so much easier. When we refer to tools, in its plural form, we imply that there are more than one. We will look at the different types of diagnostic tools in use; we will also learn about what a vehicle diagnostic exactly entails.

The different types of diagnostic tools

It is very important, due to the immense amount of electronic components that regulate so many vehicle functions, to use the right diagnostic tool to detect and identify problems. According to Schueller (2015), there are mainly three types of scan tools available in the automotive aftermarket domain: the On-Board Diagnostic Level Two (OBD-II) generic and OBD-II enhanced tool and then there is the factory scan tool.

OBD is a standardized system that allows external electronics to interface with a vehicle’s computer system with the primary purpose of performing a diagnostic test. When a vehicle’s sensors detect an anomaly, it triggers a trouble code that may manifest as a “check engine” light or other dashboard warning. An OBD scanner can check these trouble codes to determine exactly what is wrong, and then clear them from the computer’s memory once the problem is fixed. Many people – in our experience – have little knowledge about the meaning of these codes. Let us therefore quickly peek at these codes, by doing so the uninformed vehicle owner may have a better understanding of them.

According to autointhebox.com, each letter and number in the diagnostic trouble code can represent a different part of the vehicle. It is important to note that the digits mentioned here may vary by vehicle make, but usually they indicate the following. If the first letter is a “P”, it will refer to the power train. The letter “B” will relate to the body, a “C” to the chassis and a “U” is undefined. The number zero in the second placeholder is a generic code shared by most manufacturers, but some manufacturers may use a specific code here, the number 1 may then appear. The third placeholder determines the area of the problem. In this regard, the numbers may indicate the following:


1 – Fuel or air problem.
2 – Injector circuit issue.
3 – Ignition problem or engine misfiring.
4 – Emission control problem.
5 – A speed or idle control problem.
6 – A computer or output circuit problem.
7 and 8 – A transmission problem.

The fourth and fifth placeholders identify which system is malfunctioning.


There are many code readers available on the market and they are usually handheld devices specifically designed to detect common vehicle problems. The most commonly used code reader will provide the user with OBD-II generic information. There are different tiers to the capabilities of code readers, and there is a simple logic to follow here: the more expensive the code reader (scan tool), the more capabilities it will most likely have.

The factory scan tool, as mentioned earlier, is a tool specifically made by and for the original equipment manufacturer (OEM), which means that every OEM has its own factory scan tool. The best option is to opt for an OBD-II enhanced scan tool, because it can complete the diagnostic process on a wide range of makes and models. What makes the OBD-II enhanced model so attractive is that it includes bidirectional tests (actuator tests and adjustments) that the generic model cannot.

You may have a picture in your mind of a machine/scanner, be it a stationary or handheld one, used to diagnose the vehicle’s ECU, and there it ends. What you may not know is that there are other types of diagnostic tools available. You may be acquainted with these but you may not know that they are also diagnostic tools in the true sense of the word. Let us have a look!


The tyre pressure gauge

Your vehicle’s tyres are a very important part and need to be correctly inflated. A tyre pressure gauge will quickly diagnose the inflated state of your vehicle’s tyres and indicate whether it is inflated to the correct pressure or not.


Circuit tester and multimeter

Whenever you need to diagnose a fault in an electrical circuitry, or even to check the voltage level of the battery, you will require a multimeter or circuit tester that can measure voltage, electric current, electrical resistance and other electrical values.


There you have it. We will now touch on the extent of a diagnostic test done by a reputable workshop.

What does a diagnostic entail?

In most cases a diagnostic test can be completed in a matter of minutes, but not everybody are familiar with what exactly is done during such a diagnostic? When you bring your vehicle to us, we will hook it up to a machine that uses software that will accesses your vehicle’s computer processor, sensors, and microchips. The diagnostic test will inform us about the condition of your vehicle’s engine, such as ignition timing, level of build-up in the engine, the performance of the fuel injector, firing of the ignition coils, engine rpm levels, air and coolant temperatures, airflow, crankshaft and camshaft position, throttle opening, transmission, exhaust system, brakes, etc. By manner of this diagnostic session, we can pinpoint any problem areas that may require attention.

Brian England (2017) compiled some steps taken during a typical diagnostic procedure. These steps will give you an additional understanding of what you can expect when you have your vehicle diagnosed.


Step 1: The technician will interview the vehicle owner and document the symptoms.

Step 2: The technician will then conduct some basic vehicle checks.

Step 3: The technician may then check for any service updates related to the symptoms described by the vehicle owner. This refers to failures that may occur due to a faulty batch of parts, which may result in recalls and service updates.

Step 4: The skilled diagnostic technician will then conduct a logical systematic diagnostic procedure.

Step 5:  Technicians may at times need to contact a technical support hotline in order to share data; the hotline may then work together with the technician to diagnose the problem efficiently.

Step 6: Once the problem is diagnosed, the technician will report the findings to the vehicle owner.

Step 7: An estimation of the repair costs will be shared with the customer in order to get approval to proceed. Sometimes a defective part may need to be replaced in order to continue the diagnosis itself.

Step 8: Once the problem is repaired, the technician will run another diagnostic on the vehicle. The data of the diagnosis are usually saved in the computer.

Step 9: The technician will finalise the documentation regarding the repairs done.

Step 10: Once everything is documented, the vehicle is given a test drive before it is ready to be returned to the customer.


You may now have a better understanding of what a vehicle diagnostic is and what it entails. A few last words in this regard. Keep in mind that a skilled technician usually have good critical thinking and problem solving skills. Why is this? It is simply because these are essential skills to have whenever you have to assess and identify a problem in a computerised vehicle where dozens of things can go wrong in a myriad number of ways. This reiterates the fact that a thorough diagnostic scan should always be conducted by a reputable workshop with trained and skilled technicians.

It will also do you no harm to have your vehicle regularly diagnosed, because we hope you know that early detection is far better than costly repairs (or being left stranded) later. Furthermore, the ‘check engine light’ should not be your cue to have your vehicle diagnosed. Practice a proactive approach to vehicle maintenance by including frequent diagnostic scans into your personal maintenance schedule. Some more sound advice; if you consider buying a used vehicle, then have the private seller or dealer agree to a diagnostic test before you commit to buying it. Do you too smell something fishy if they refuse to have a diagnostic test done? A clear sign that you should walk away from the deal.

Steves Auto Clinic is a leader in the field of automotive servicing and repairs. We have all the expertise, all the equipment, and all the friendly faces to give you an experience that will WOW you. Bring your vehicle to one of our branches and have your valued possession diagnosed.

Sources consulted during the writing of this article: