Car Diagnostic: What is it, and how does it work?

Car diagnostic
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Car diagnostics can detect several important pieces of information about the vehicle. Today, it is hard to find a car not equipped with an engine control unit (ECU / ECM). It is a microprocessor (or simply a small computer) that evaluates and stores a whole range of information.

The warning light on the dashboard then alerts the driver of a problem identified by the ECU. Though the illuminated warning light won't tell you much, to get detailed information about the problem, we need to access the car's database (memory) through car diagnostics.


What is a car diagnostic?

Car diagnostics can take different forms, but it is a special device or software. As already said, the purpose of car diagnostics is to be able to read various data that the engine control unit stores in the database. Thanks to this, we can evaluate major or minor malfunctions using error records and get more detailed information about the problems of a specific vehicle.

In addition to reading error records, we can use car diagnostic to change or delete specific data in the database or change the control unit's (ECU's) settings.

Basic car diagnostic functions

  • Reading error logs, displaying error history, etc. (reading information stored by the engine control unit)

  • Editing and removing error records

  • Changing or adjusting the settings of the control unit (oil change interval, etc.)

  • Emission diagnostics

Types of car diagnostic

Car diagnostics can take the form of a professional device - an electronic device equipped with specialized software. Such car diagnostics have a wide range of functions, and they are mostly used by authorized and professional car repair shops, as these devices are among the most expensive on the market.

More affordable car diagnostics can take the form of a specific connector, thanks to which we can connect to the engine control unit using a computer or smartphone. Of course, with a lower price comes limited functionality; as a rule, the cheapest car diagnostics can only read basic data.

OBD and car diagnostics compatibility

For car diagnostics to read data from the ECU, or vehicle control unit, it must be compatible with the given vehicle. Some car diagnostics are manufactured only for a certain brand, but there are also universal types of car diagnostics.

The standard of the control unit is important for the compatibility of car diagnostics with a specific control unit. These are the following:

  • OBD / OBD 1

  • OBD 2

  • EOBD

  • JOB

Older vehicles had control units that were not subject to any standards. This means that they use different communication protocols and thus may not be compatible with many car diagnostics. In the case of these vehicles, it is the OBD / OBD 1 standard ("OnBoard Diagnostics" - the full text of this abbreviation in English).

OBD2 connector

Newer cars have already switched to a single standard, namely OBD 2. European vehicles largely switched to this standard in the early 2000s, including diesel cars from 2003. The EOBD and JOBD standard is no different from OBD 2 and is ultimately the same standard. In the case of EOBD it concerns European cars, and in the case of JOBD, it concerns Japanese cars.

However, when choosing car diagnostics, you need to be careful about whether it is the OBD / OBD 1 standard or the newer OBD 2 standard. These are not compatible - for example, car diagnostics for older vehicles with the OBD 1 standard will not work for newer vehicles that use OBD 2 standard and vice versa.

The best car diagnostics

The choice of car diagnostics depends primarily on the buyer's needs - if it is a car service, the smaller ones can get by with advanced, but many prefer professional auto diagnostics.

For an ordinary person, basic car diagnostics, which allows basic data to be read from the control unit, will probably be sufficient. It is, therefore, difficult to recommend a specific brand, as the choice depends primarily on the need and purpose.

Car diagnostics price

The approximate price range for different car diagnostics of different types.




from 750 to up to 4000 Euros


from 100 to 400 Euros

Basic (read-only)

up to 50 Euros

Regardless of the type, thanks to car diagnostics, some problems can be identified and eventually solved. Thanks to basic car diagnostics, one can avoid visiting the service center, which charges for simply reading error messages.

Of course, we do not recommend editing or deleting error messages or modifying other settings through car diagnostics - leave that to the professionals at the car service.