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VEHICLE DIAGNOSTICS, WHAT IT IS AND HOW IT WORKS

26.04.2022

Modern cars, with their degree of complexity, set new requirements in the field of automotive diagnostics. Determining the causes of the defect and indicating the components to be replaced can turn out to be quite a challenge. The number of automotive diagnostics solutions is very large, but the way in which a diagnostician uses them is crucial.

WHAT IS VEHICLE DIAGNOSTICS

Car diagnostics is associated among drivers with periodical roadworthiness tests for motor vehicles at diagnostic stations. Such an examination, required by law, focuses on the issues of driving safety and environmental impact in accordance with the applicable standard. Another association is computer diagnostics, which consists in connecting the diagnostic interface to the OBD2 connector and reading various data in this way. In fact, car diagnostics is a very broad concept and covers many more issues.

In terms of methods and tools, everything depends on what vehicle systems we want to test. We will look for faults in the suspension differently, check the operation of the braking system differently, test the engine differently or determine the causes of air conditioning failure. The methods can be divided, for example, like this:

  • Self-diagnosis, i.e. the use of diagnostic functionalities by the engine controller (computer diagnostics);
  • Diagnostics using independent testers and gauges in the vehicle (e.g. battery tester, compression pressure gauge);
  • Diagnostics of components outside the vehicle (e.g. testing of injectors on a test bench);
  • Organoleptic methods – subjective evaluation of a mechanic based on visible traces, sounds, vibrations, etc.

The service technician who performs the diagnosis is responsible for the selection of appropriate tools depending on the situation – whether he wants to find the cause of the engine failure or prepare a report documenting the current technical condition of the car at the time of changing the owner..

COMPUTER DIAGNOSTICS VIA THE OBD 2 DIAGNOSTIC INTERFACE

This method of diagnostics is so obvious today that some people forget that it is not the only one based on which a car can be diagnosed. Thanks to the standardization of diagnostic methods under OBD 2, service technicians have been guaranteed access to basic car data for over 20 years. The greatest advantage of the method is speed – connecting the computer to the connector in the vehicle takes only a few moments, and usually does not require disassembly of any elements.

DIAGNOSTIC SOLTUTIONS

Although the connector is one, there are many offers and testers in the distributors’ offer. They differ in their ability to diagnose cars of various brands and models, as well as additional functionalities or support from the manufacturer. The interface with the appropriate software is one that will use as many opportunities as possible from the ECU. Because you have to remember that this method is based on the accuracy and range of data from the engine controller. This means that we read the signal status from a specific sensor, but if the signal is incorrect, we do not know whether the problem is the sensor or the wiring, or damage to the controller itself.

LIMITATIONS

Here we come to the crux of the limited reliability of the ECU data. This does not mean that we should avoid computer diagnostics. However, it is necessary to be aware that the trouble codes read through the diagnostic interface are not enough. The content obtained in this way should be critically analyzed. The trouble code can, in particular, mislead an inexperienced service technician. It may also be the case that, using the computer, we will not obtain any data indicating a defect despite their obvious presence.

INDEPENDENT METHODS OF DIAGNOSTICS

There is one more division of diagnostic methods – into serial and parallel diagnostics. The serial one is the one described previously, the point is that the data we got through the OBD connector in the car has all passed through the ECU and is dependent on it. Parallel diagnostics is the one that is based on a parallel measurement, e.g. using a multimeter, oscilloscope or other dedicated tester. The name of the method comes from the devices offered for the diagnosis of early electronically controlled engines. These were special modules attached between the controller connector and the vehicle-side plug, providing the possibility of independent access to the inputs and outputs of the controller.

Over time, the development of on-board diagnostic methods has gave way to such solutions. Controllers were expected to pinpoint the causes of a car’s failure so accurately that many testers and diagnostic methods would be needless. It turned out completely different, which results from both technical limitations and the policy of automotive companies. Keep in mind that vehicle service and parts sales can provide quite a lot of profit. It is hard to expect that the giants will deprive themselves of the ability to shape this market.

UNDERESTIMATED OSCILLOSCOPE MEASUREMENTS

Oscilloscope measurement is a flagship example of parallel diagnostics, giving great diagnostic possibilities not only in the specialized vehicle electronics workshops. Thanks to easy-to-use and safe automotive oscilloscopes such as the Scope DT, measurements can be made in any workshop. There is a misconception that performing oscilloscope measurements is reserved for a narrow group of specialists.

The truth is that the measurements in each case are new valuable data, and only the experience and knowledge of the user will depend on how he will use this information to find the fault.

DEDICATED TESTERS

Another group of devices are specialized testers, designed to test specific components or entire systems of the car. An example of such a tester is EDIA-PRO, an oscilloscope tester for the Common Rail system. This tester collects completely independent diagnostic data such as injectors signals, operation of control valves or rail pressure. Thus, it provides valuable guidance in deciding whether and which components of the injection system should be submitted for further testing.

In the case of diesel vehicles, the DTE offer also includes SIT-12, a tester that allows you to test the injectors from the electrical side, both inside and outside the vehicle. In turn, thanks to the RPT-5 device, we have the possibility of fully parallel pressure measurement on the rail, much faster than any tester connected to the diagnostic connector can perform.

Another example of a dedicated diagnostic tester is the DBT-12 +. It allows not only to easily perform a battery test, but also to perform advanced starting and charging measurements, presenting clear messages about each of the tested systems. Data can be exchanged with a computer for convenient storage or printing of reports.

 

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INVEST IN DIAGNOSTICS TODAY

You too can diagnose better. Investing in new diagnostic methods is not only about new workshop equipment. The key is to understand what car diagnostics is and how multi-dimension the process is. Even the best equipment cannot diagnose the car on itself. The knowledge and experience of a service technician, gained both during various training courses and during everyday work with cars, is extremely important. Introducing good and effective diagnostics is the key to an efficient service. Quick detection of faults is the key to their efficient removal. There is no better advertisement for a workshop than recommendations from satisfied customers.

 

Autor: Inżynier Produktu Piotr Libuszowski

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