What Do OBD and OBD-II Mean?

These monitoring systems and trouble codes are a window into your vehicle’s inner workings.

OBD DonglesAustin Lott | Capital One

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Today's vehicles provide a host of computer controls, sensors, and systems that make it much easier to diagnose potential problems (and then better target their repair). Although car companies have experimented with this technology since the late 1980s, the modern version dates back to 1988, when California mandated some type of onboard diagnostic or OBD capability in all vehicles sold in the state.

This requirement evolved into what is known as OBD-II, which arrived in 1994 and became a federal requirement affecting all vehicles sold in the United States two years later. The OBD-II specification offers a much deeper look into a vehicle's various systems, and it remains the standard today.

Here's a look at the benefits of OBD-II and how it fits into the current automotive landscape.

What’s the difference between OBD and OBD-II?

Early OBD systems were primarily focused on two things: engine management and tailpipe emissions. As Environmental Protection Agency (EPA) regulations became increasingly stringent, car companies deployed a number of different emissions control systems that were monitored by computers. At the same time, computer-controlled fuel injection was displacing carburetors and early mechanical injection as the 1980s progressed. OBD featured sensors that monitored the control and performance of these types of systems.

OBD was largely a hodgepodge of efforts from different car companies, without any cohesive protocols. This changed with the introduction of OBD-II, which offered a standardized way for electronic vehicle systems to monitor functionality, report on any issues, and respond to queries from technicians.

How do OBD and OBD-II work?

OBD and OBD-II are based around an electronic control unit/module (ECU or ECM) that keeps track of data provided by an array of sensors integrated into various vehicle systems. If a problem arises, these sensors send a trouble code to the ECM, where it is stored for later access. Sometimes, these codes will illuminate the “Check Engine” light on the vehicle’s dashboard, indicating that a code is saved in the ECM’s memory.

How is OBD information accessed?

In order to “read” an OBD error code (also known as a Diagnostic Trouble Code or DTC), technicians connect a scan tool or reader to the vehicle's OBD port. Sometimes this is a handheld tool, and sometimes it's part of a larger computer diagnostic system. Owners can purchase their own tool or use a phone app connected to a dongle that attaches to the OBD port to read these codes.

As of OBD-II, these tools are standardized and use the same type of port, but earlier OBD implementations can feature manufacturer-specific designs. Some older vehicles can also display codes by flashing lights according to patterns specific to that model.

There are plenty of online resources that can translate a stored code for you, allowing you to understand what vehicle systems are experiencing an issue. It can be quite useful to know what DTCs are stored prior to visiting your mechanic, as it gives you a general idea of what type of repair might be required or if you can address the problem yourself.

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Benjamin Hunting
Benjamin Hunting is a writer and podcast host who contributes to a number of newspapers, automotive magazines, and online publications. More than a decade into his career, he enjoys keeping the shiny side up during track days and always has one too many classic vehicle projects partially disassembled in his garage at any given time. Remember, if it's not leaking, it's probably empty.