Car Diagnostic Test

Planning for a Car Diagnostic Test? Here is Everything you Need to Know.

Daniel McDonald
Daniel McDonald8 min read
Planning for a Car Diagnostic Test? Here is Everything you Need to Know.

Planning for a Car Diagnostic Test? Here is Everything you Need to Know.

Ensuring your car is in suitable condition is vital since you don't want to get stuck in the middle of your journey. So, if there is any unusual sound, look, or smell from your car or the check engine light comes on, you might want to take it for a car diagnostic test.

The test will help you determine the issue with your car. While you can do a car diagnostic test yourself, getting a professional to look at it to identify all issues is better. We will discuss the details of the car diagnostic test to give you a better idea about it.

You can also learn about the DTC in this guide. Let's start by understanding a car diagnostic test and its importance.

What is Car Diagnostic Tests?

The car diagnostic test (also known as the engine diagnostic test) are analysis systems that experts use to identify the critical issues with significant components of your car. The check engine light in your dashboard indicates an issue with your car.

The overall engine diagnostic system has evolved much since it first came out. Today, technological advancements have given the computers the access to various subsystems in cars, like:

  • Active handling systems

  • Advanced all-wheel drive

  • Navigation

  • Safety features

  • And a lot more

In the initial days of the electronic fuel injector, you would have to use multiple systems from each manufacturer to write code for your car's computer systems. The computer would then inspect the car with the engine on and check all the sensors and other vital elements are working fine.

This system was the first period of the onboard diagnostic systems, becoming quite common in the coming years. However, it was a hectic job for mechanics to operate the vast number of computer systems from various manufacturers.

These mechanics didn't want to invest much time and money in buying and setting up every manufacturer's systems for diagnoses. Therefore, the Society of Automotive Engineers set new standards for the onboard diagnostic systems to resolve these issues for technicians and vehicle owners.

It led to the creation of the OBD-II standard, which had a diagnostic plug below your dashboard. Moreover, it simplified the diagnostic language for any system to read it.

The rapid standardization provided a pathway for the diagnostic trouble codes. These codes made it easy for technicians and even day-to-day drivers to conduct OBD-II diagnostics.

How Does the Car Diagnostic Test Work?

The car diagnostic test is about running an analysis of your vehicle of vital components and digital systems. Vehicles nowadays have many more digital systems that help them run properly. Many people are unaware of all the computer systems, so they need a car diagnostic test.

There is specialized software that will check the vital components of your vehicle when the engine is on. The software will gather and make data reports for further analysis when performing a diagnosis.

Mechanics can scan your car during the diagnostic test to ensure all the critical components are operating properly, such as the oil tank, engine, transmission, etc.

Since the car diagnostic tests need specialized software and expertise to perform and find any possible issues, they are conducted by a professional technician at an auto repair or dealer shop. But that does not stop you from performing a car diagnostic test.

You can do it at home if you have the mechanical knowledge and the equipment to run the test. If your car's dashboard shows a check engine light, you can run a simple diagnostic test to look for problems with the engine or any other issues. You can also ask your technician to run these tests during the maintenance appointments.

How Do You Know There is a Problem with Your Car?

Nowadays, it's rather easier to find out what's wrong with your vehicle. With the vast information and current tech available with just a click of a button, you can rest assured your problem will be fixed in a nano-second!

So let's take a peek at some simple signs.

For instance, modern vehicles' OBD system will turn on the check engine light (also known as the dashboard warning light) when it notices an issue with its performance. The system will register a code that tells you about the ongoing problem with your car.

This code is known as the Diagnostic Trouble Code (DTC), incorporated into the OBD system. You can access the stored information by connecting a scanner or other diagnostic tools to the socket. The scanner will read the code and let you know about the possible issues with the car.

You can find out whether the issue is with your engine system or any other critical component that needs attention as soon as possible. Once you identify the issue, you can check the handbook to know what steps you need to take per the car's make and model.

What is a Diagnostic Trouble Code?

The DTC is the code with five digits that determine specific issues with your vehicle. Diagnostic Trouble Codes come up on the scanning tool when you connect them to the car's onboard diagnosis system.

The code comprises one letter and then four numbers, such as P1234. The letter and the numbers tell you about a specific problem with a car which can be a standard-issue or severe malfunction. Whenever you see your check engine light blinking, it is better to get it inspected by your local mechanic.

They can run the diagnostic test and do a visual inspection to find out the possible issue with your car. Though the DTC won't determine the exact problem with the part you need to replace or fix, it will give your mechanic or you an idea of what test you need to do to diagnose the problem.

How Can You Read Diagnostic Trouble Codes?

You will find a wide range of DTC that vary from manufacturer to manufacturer. Therefore, you must check your vehicle's manual to read the diagnostic trouble code.

Usually, one of the letters (P, B, C, U) will come before the number and help you relate to the part facing the issue. For instance:

  • P refers to the powertrain

  • B indicates the problem with the body

  • C tells their an issue with the chassis

  • U highlights a problem with the network

After the letter, the second digit in the code will either be a 0 or 1. The number 0 indicates a generic issue, whereas 1 indicates a problem related to the manufacturer. The third correspondent tells you the problem with a certain system, such as brakes, ignition coils, or any other major component.

Remember that the third correspondent in the codes can be either a number or a letter. The last digits will be numbers that show the precise fault description. You won't find any decryption key to decode these last two numbers.

Benefits of Car Diagnostic Tests

A car diagnostic test can open you up to many benefits. It can be challenging to judge the actual problem on your own. But with the help of a professional technician, you can perform a car diagnostic test in no time and enjoy the following benefits:

  • The test assists you uncover minor problems before they become significant issues in your vehicle.

  • It helps you save time and money in the long term since you won't have to deal with the cost of hefty repair work.

  • The car diagnostic test ensures that your car is in perfect condition to drive, keeping you and others safe.

  • The tests highlight possible issues with your car's engine, exhaust system, brakes, ignition coils, and other critical parts.

  • The tests also look for the OBD system for any stored information or manufacturer notifications. This information gives technicians a better idea regarding the repairs your vehicle needs.

When Should You Go for a Car Diagnostic Test?

Most drivers tend to perform an engine diagnostic test or during regular car maintenance checkups, and other drivers might wait until the check engine light turns on in the dashboard.

They will then take their vehicle to the local mechanic to check for possible issues with the car's engine or other major components. Technically speaking, you don't need car diagnostic tests regularly, and the mechanics perform these tests using a specific tool for software to speed up the repair process.

They can assess the issues quickly and provide you with a better service through it. If you want, you can learn how to perform a diagnostic test and do it without any technician. However, it would help if you had complete mechanical knowledge and the equipment to repair parts and fix minor issues.

Most importantly, you can prevent your car from severe malfunctions in the future. If you choose to do a car diagnostic test, you should do it after every season.

How Much Will it Cost If you Go for a Professional Mechanic?

The charge of the test will vary depending on the car's make, model, and the issues identified with your car. If no significant repairs are necessary for your vehicle, the charge should be around $40 to $50.

But, if the mechanic will need to run some more tests for further analysis and the major components would need some repairs, then the expenditure can go up to a few hundred dollars. The technician will let you know the exact expense after finding out the severity and intricacy of the car's issue.

Repairs with the car's components, such as the engine, transmission, etc., might cost you significant money. Also, it is best to check the fine print in the service agreement when you plan to sign up for the car diagnostic test.

There is a slight chance that they will claim to give you a free service for the test but might have some hidden charges mentioned in the service agreements. So, going through the contract with complete focus is vital to avoid missing out on any such essential details.

How To Perform the Diagnostic Tests if The Check Engine Light Turns On?

The first thing you would need is a wireless OBD-II reader to plug it into the port in your car. Next, you need to download a mobile app such as BlueDriver, Torque, etc. After connecting the reader with your car, the app will act as a code reader.

The app will help you read diagnostic trouble codes and identify the issues with your technical knowledge. However, not all mobile apps work with the OBD-II reader, so check the compatibility before buying them.

You can also go for a professional code reader to give you an in-depth review of the diagnostic codes. These code readers are a bit costly and offer you a wide range of things, such as:

  • Large display

  • Multiple languages

  • In-depth diagnostic capability of subsystems

  • And much more!

However, these sort of systems is better for commercial purposes. So, if you plan on opening an auto repair shop in the future, you might get a professional reader. But if you want to perform the diagnostic test for your car, then the standard OBD-II reader will do the job for you.


The engine diagnostic tests can help you identify your car's potential issues and ensure it operates properly. You can go to the nearest dealer shops and get the tests to avoid any major repairs that can burden you financially.

Also, you won't have to go through a lengthy process that can take days to fix the issue. If you have the proper code readers and other tools necessary to conduct car diagnostics, you can do it yourself. The investigative work will help in identifying problems that have the potential to become serious issues later.

Since you know your car more than anyone, you might know if there is anything wrong with it. If you feel something is wrong, you can go to your nearest service center for regular diagnostic tests. The technicians can perform engine diagnostic to ensure there is no problem with it and check the other car's components.

Also, keep a close eye on your check engine light since it indicates potential problems. If you see the light coming on, then it is time to run some car diagnostic tests to identify underlying problems that can become massive problems in the long run.