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The Basics of Automotive Diagnostics

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Cars are a lot more complicated than they used to be. All modern cars on the road today have an interior computer that's connected to sensors and electronic devices inside the vehicle. When you get a check engine light, it's because the computer has identified a problem in one of the car's systems. In order to find out exactly what's wrong, the car's on-board diagnostic system is plugged into a scanner that interprets the diagnostic codes so your mechanic can identify the problem. Let's find out how the codes and translations work.

Different Types of Scanners

Today anyone can buy a simple code reader, and there are even apps that can turn your phone into a scan tool. Most of the information needed to interpret scancodes can be found online, so a 'check engine' light no longer means you have to immediately call your mechanic. It's important to realize that these readers don't automatically tell you how to fix a problem. In most cases all it will do is provide you with the trouble codes that can point you in the right direction.

There are three types of scanners available for mechanic shops; OBD-II generic, OBD-II enhanced and factory scan tools.There are different tiers to what code readers are capable of. The basic functionality readers, such as OBD-II generic, can read and clear codes, and provide a fast reading of emission based trouble codes. They're best used for completing a preliminary analysis of vehicles that come into shops with the 'check engine' light on. This tool can give an indication of what to include on initial repairs.

These basic functions, however, make the generic models a limited-use tool for complex vehicle diagnostic issues. Higher end readers can provide further functions, such as giving definitions of OBD-II generic codes, as well as pending codes, freeze frame and permanent codes. Just like computers, scanners require an operating system to run. Many scanners now run off an Android-based operating system, although a Windows version is also available.

Running a Diagnostic

When performing a diagnostic, a scanner is plugged into a port called the OBD-II port. This port is standard in all vehicles sold in the US after 1996. Vehicles before this time had a very limited diagnostic system that varied between manufacturers. During the diagnostic, you'll receive codes like P0301, or B-1402. These types of codes are standard across the automotive industry, apart from a few manufacturer specific codes. Codes that start with a B, are body codes, P codes are for the powertrain, and C codes indicate a problem with the chassis.

Even the more expensive models don't always give a definitive answer, however. A P0301 code, for example, indicates that an oxygen sensor in bank one has a malfunction, but this could have been caused by any number of issues, including a faulty oxygen sensor, an incorrect air-to-fuel ratio, or a problem with the computer. The diagnostic will point you in the right direction, but now the experienced technician has to take this data to accurately pinpoint the malfunction.