Introduction to OBD-II

First, you have to understand how the OBD2 system works. 

To demonstrate that I will use my Renault Kangoo (it had 4×4, pretty fun thing to fu*k around with, but some car had to be sacrificed)

I pulled out the engine and dashboard wiring from it.

So now I have this on my desk.

It looks complicated, but the OBD2 system is basically just software stored inside your ECU (engine control unit).

All sensors in this complicated wiring are reporting data directly to the ECU. Then the OBD2 system (software inside the ECU) will look at this data to see if anything is OFF based on learned values.

If anything is wrong or out of the specified range, it will set a fault code. For example, if the voltage from the O2 sensor is less than usual, it will store a fault code (DTC) inside ecu memory.

All we do with a scanner is connect to the ECU memory and read already stored fault codes. 

But this is only the engine control module. In a modern car, you can have easily even 30 different modules, but they all work on the same principle. 

Car sensors collect various data

There are hundreds of different sensors in your vehicle, collecting data about everything going on in each sub-part of your car!

Sensors send this data to control modules

Sensors send collected data over to different control modules. Each control module manages different sub-parts of the vehicle while also communicating and sharing data with other modules.

OBD-II system evaluates all of this data 

All these control modules and sensors connected together form a powerful OBD2 system that knows the right parameters for every collected data from the factory.

If any data isn’t in a specified range…

Let’s say one of your sensors reports data out of the allowed range. This will automatically set the code in the control module memory and, in many cases, trigger some warning light on your dashboard, for example, the “Check engine light.”

How OBD Started

OBD, or On-Board Diagnostics, originated in the 1980s as a way for automotive manufacturers to monitor and control engine performance and emissions.

The first systems, known as OBD-I, were simple and varied between manufacturers. They provided basic diagnostics but lacked standardization, making it difficult for technicians to work across different car brands.

OBD-I vs. OBD-II

OBD-I was the initial attempt at automotive diagnostics, offering limited information and differing widely between manufacturers. OBD-II, introduced in 1996, standardized the diagnostic system across all vehicles sold in the United States.

OBD-II provides more comprehensive data, allowing for better engine performance monitoring and easier troubleshooting.

Key differences:

• Standardization: OBD-II is consistent across all manufacturers.
• Data: OBD-II provides more detailed and extensive diagnostic information.
• Ports: OBD-II vehicles have a standardized 16-pin connector.

Which cars have OBD?

All cars and light trucks sold in the United States since 1996 are equipped with OBD-II. For other regions, the mandatory use of the OBD system came later, but nowadays most cars manufactured after 1996 will have it. 

That’s it, now you know how OBD2 works.

Yuri

P.S. If you are more of a visual learner (video), you might want to check out my DIY Smart Mechanic video program