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A mechanic is checking a car's electrical system.

Understanding Car Diagnostic Systems

Cars are incredible and intricate pieces of machinery that are composed of several different moving parts and components. These parts must all be working correctly and in unison for the car to achieve safe motion. Due to the sheer amount of components and systems that go into a vehicle, vehicle maintenance is an unfortunately common occurrence for the average vehicle owner. Whether it be engine repairs, radiator repairs, or even car electrical repairs, your vehicle will require some sort of maintenance.

Some things are definitely easier to determine, and can even be diagnosed at home by the owner. For instance, brakes that are old and need to be replaced will start to feel less-effective while braking, and may even cause a loud grinding noise. A vehicle with an exhaust leak will sound louder while driving, as well as require the engine to run harder than it normally would. However, there are certain things that are very small that would not be readily identifiable by even a trained eye. These are usually smaller electronic items such as sensors and switches, which are usually buried in the vehicle’s engine.

It can be very difficult to determine the status of something so small and minor, which is why vehicles have a system that is dedicated to monitoring the status of these things, as well as things such as oxygen levels and emissions. All modern vehicles have a diagnostics system that is constantly monitoring the vehicle. If something is wrong, this system will usually trigger your service light to come on, which lets you know that it must be brought to a mechanic.

What is an Onboard Diagnostics Systems?

An Onboard Diagnostics System, or OBD, is a sort of computer-like component that comes equipped in a vehicle. This computer is responsible for scanning the vehicle and tracking things like emissions, O2 levels, electrical output, and the statuses of several different components. This allows the vehicle to alert the owner when certain components fail that would be difficult to individually keep track of, like O2 sensors and leaks in the EVAP system. Due to the designs of vehicles, most of the smaller sensors and switches are in hard to reach areas, so they cannot be tested normally. The OBD system is able to constantly scan the status of the vehicle while it is running, and can alert the owner to issues.

Once the vehicle is in the hands of a mechanic, they are able to connect an OBD2 scanner device to the vehicle via a small connector underneath the steering console. The OBD system sends error codes to the scanner, which the mechanic is then able to use to determine the exact issue.

History of OBD Systems

While the first standardized OBD system did not come into existence until the late 1980s, the first example of an OBD system for cars actually came out in the sixties. In 1968, Volkswagen created the first OBD computer system with scanning capabilities. This was rather limited in its applications; however, it was considered a breakthrough nonetheless. This was improved upon slightly by Datsun, who released their own non-standardized simplistic OBD system ten years later.

Then, in 1980, GM released its own take on the OBD system, which was a proprietary interface that was capable of providing engine diagnostics through the use of an engine maintenance light. At this point in time, many different car manufacturers began releasing OBD systems for their vehicles.

A mechanic is testing the OBD system with a code reader, the first thing you do when starting a car electrical repair.

While this was certainly beneficial for the automotive market and helpful for mechanics, over time, this actually started to become a nuisance for mechanics. Each carmaker had its own unique OBD system, which would utilize different sets of error codes. This made trying to read error codes a serious pain, as mechanics would have to learn and memorize a whole slew of codes for each individual car maker. Sometimes, these car makers would even use different OBD sockets, requiring mechanics to have to purchase additional tools that would not be utilized very often. The automotive world realized it needed to standardize the codes for OBD systems, which happened in the late 1980s.

In 1982, the California Air Resources Board (CARB) met and passed regulations that would affect all vehicles sold in the state. Starting in 1988, all vehicles sold in the state of California would require an OBD system standard to detect emissions failures. This led to the first standardized OBD systems, which are known as OBDI. This was a rather simplistic system and only monitored the oxygen sensor, EGR system, the fuel delivery system, and the engine control module. While this was certainly a great move, OBDI still allowed for automotive makers to use their own unique connectors. With certain vehicles, the only way to get your engine light checked was through a costly trip to the dealership.

Due to the limitations of the system, the CARB developed a new set of standards for cars sold in California, along with a whole new OBD system, which is known as OBDII. Included in the set of new regulations was a standardized adaptor along with a standardized set of codes. This universal regulation ensured that anyone with an OBDII code reader could check the statuses and codes for any vehicle that has OBDII, which greatly helps out anyone who has to service vehicles.

These regulations also required twice the amount of O2 sensors, a more powerful powertrain control module, a more sophisticated evaporative emission control system, and sequential fuel injection, among other upgrades. The OBDII was a massive success and is still utilized to this day.

Reading OBDII Codes

The OBDII system in every vehicle monitors a number of different systems for possible errors, and there are a number of different things that can cause it to light up the maintenance light. There are two primary codes that can cause the light to go off, type A codes and Type B codes.

Type A codes are considered the most-dire and will set the maintenance light off after only one occurrence during a single driving cycle. Type B codes are not as drastic as type A codes, and will only set the light off after two occurrences have been recorded by the OBDII system. Once the maintenance light is on, an OBDII scanner must be attached. Once attached, the scanner will show any error codes that exist. These error codes are five total digits and start with a letter followed by four numbers (like C1234).

The letter determines the area where the code has been detected, and there are generally four different categories. B indicates the body and covers things that are inside the passenger compartment. C indicates chassis and includes things like brakes, steering, and suspension. P indicates powertrain and includes components such as the engine, transmission, and accessories such as turbos. And U indicates network and vehicle integration, which covers things such as the diagnostic system itself.

The numbers also help pinpoint the exact issues the vehicle is having. The first number typically determines whether or not it is a generic code that is shared universally or a manufacturer exclusive code. If it is a 0, it is generic, and if it is a 1, it is a manufacturer code. The second number indicates the particular subsystem that is affected. The last two numbers indicate what the actual issue is that is causing the error code. By becoming familiar with OBDII codes and getting a scanner, you can determine any engine code that may set off your maintenance light from the comfort of your own home.