OBD stands for onboard diagnostics and OBD-II is a collection of connection and protocol standards standards for all cars sold since 1996, when the OBD-II specification was made mandatory by the U.S. government.
OBD technology was born out of the Environmental Protection Agency's (EPA) and California Air Resources Board's (CARB) mandate that vehicles equipped with more-sophisticated emissions equipment and better diagnostics systems to monitor that equipment. The agencies wanted to ensure that new vehicles were running as cleanly and efficiently as they could. However, purchasing diagnostics equipment for each of the manufacturers' proprietary vehicle information systems would be prohibitive for third-party garages and testing centers. Thus, the OBD standard (and the subsequent OBD-II revision) was born.
The first part of the OBD-II standard is the connector. The 16-pin female interface connector must be located in the vehicle's cabin within 2 feet of the steering wheel. For most cars, this means in the driver's foot well or just below the steering wheel. Although, the physical connection is always the same in OBD-II-compliant vehicles, not all of the 16 pins are always utilized and the data isn't always sent over those pins in exactly the same manner, so there is some variation within the standard. Specifically, there are five major signaling protocols for vehicles sold in the United States between 1996 and 2008 that can usually be discerned by the configuration of pins used. New legislation has narrowed these five variations down to one, ISO 15765 CAN, for all vehicles sold after 2008, so the OBD-II standard is decidedly more standard from that point forward.
Outside of the US OBD-II standard there are also the European EOBD and EOBD2 standards and the Japanese JOBD standards.
What does it do?
Where the real work of the OBD-II standard takes place is within the data sent over the connection. During normal operation, your vehicle is constantly monitoring a little more than 100 standard Parameter ID (PID) codes. Every vehicle must be capable of sending or receiving these codes over its OBD-II connection. These codes tell the tale of the systems monitored by your vehicle's emissions system, everything from fuel system status to engine and vehicle speed to the status of the vehicle's various O2 sensors. If there is an error with any of these parameters or if a value falls outside of a predetermined safe range, the vehicle will illuminate its Check Engine light.
The vehicle's computer is able to send all of this diagnostic information over the OBD-II connection to a connected diagnostic tool via PID along with special PIDs, known as trouble codes, that detail the issue. There are about 900 possible trouble codes in the OBD-II standard reporting on everything from fuel systems to emissions controls to transmission status.This makes it easy for a mechanic or emissions official to quickly diagnose an issue with a vehicle's engine and emissions equipment without hours of guessing and checking.
In addition to the 100 or so standard PIDs, there is room in the OBD-II standard for manufacturers to include their own proprietary and discretionary PIDs and trouble codes for monitoring other aspects of the vehicle's performance that may or may not directly affect emissions, such as supplemental restraint or tire pressure monitoring systems, further extending the utility of the connection for dealers and authorized service centers. These nonstandard PIDs are often not supported by third-party OBD-II tools, but don't impede their functionality either.
Handheld scan tools
The primary purpose of the OBD-II connection is for emissions testing, but one of the first and most widespread applications available to consumers is the scan tool or code reader. These devices are sometimes battery powered, but newer units may be powered by the electricity provided by the OBD connection itself. When a Check Engine light is illuminated, these handheld devices connect to the OBD-II port and simply record and display any trouble code that the vehicle is sending. Users can then use the code to see what's wrong with the car and, once the problem has been fixed, clear the code from the vehicle's memory, deactivating the Check Engine light until the next issue arises.
These devices often just display the raw code, so you'll need some sort of code reference to know the difference between a P0302 and a P0455 (for the curious, the first means that your engine's second cylinder is misfiring and the second simply means that you've probably left your gas cap off). The most-advanced units may actually store the trouble codes in the device's memory to be retrieved later via USB and cross-referenced against Internet databases of code values and known issues, such as OBD-codes.com.
Where scan tools are designed to be connected to the OBD port for quick code reads, data loggers are designed to be semi-permanently connected to the vehicle. These smaller and often screenless devices stay with the vehicle as it is driven about, silently logging all of the information that the vehicle's OBD-II port provides.
This could be a great way to keep track of what your car has done over, for example, the last week; but for parents with teens, a data logger could be a good way to keep tabs on their young drivers' motoring habits. If Little Johnny decides to break 100 mph on the highway, you'll know about it--although, obviously, after the fact. Fleet managers can use similar technology to keep tabs on the manner in which their fleet vehicles are being driven.
Fuel economy meters
With more attention being paid to maximizing fuel economy, more and more we've been seeing devices that take advantage of the data supplied by the OBD-II port to report vehicle fuel economy using an external display. The standard PID set doesn't explicitly include a fuel economy parameter, but there is often enough information about the engine and fuel systems to fairly accurately extrapolate. However, some pre-2008 vehicles, such as our CNET Chevrolet Aveo, may supply insufficient data to these fuel economy meters, resulting in ludicrously inaccurate readings. Caveat emptor.
In addition to reporting fuel economy, some of these devices will give drivers reports of their historic fuel economy. Others will display ECO lights or graphics to coach drivers toward more miles per gallon. Some devices, such as the PLX Kiwi, offer driving challenges to help train the user to be a more efficient driver.
With all of that info about vehicle and engine speed, steering angle, and the like flowing out of a standard connection, the OBD-II port can be of great use to enthusiasts looking to measure their vehicle's performance on a granular level. Just like aftermarket fuel economy meters can extrapolate miles per gallon, OBD-II-connected performance computers can estimate horsepower, torque, and 0-60 times or provide a virtual tachometer for vehicles that weren't equipped with an OEM tach.
Vehicle specific devices can even be set to parse the nonstandard PIDs to derive data such as boost pressure or engine load.
Like most data-driven technologies (such as GPS and cellular data), the future of OBD-II technology lies in convergence.
For example, newer OBD-II scanners and readers are starting to integrate Wi-Fi technology to wirelessly connect to a nearby laptop or smartphone for easier monitoring of a vehicle in a garage or on the road. For example, the OBDKey WLAN and the PLX WiFi allow a nearby iPod Touch or iPhone to stream OBD data for use in an app such as Rev or DashCommand.
GPS device manufacturers are starting to get in on the OBD-II game as well. Earlier this year, we saw the announcement of the Garmin EcoRoutes HD system, which pulls OBD data from a Bluetooth dongle to more accurately measure your fuel economy and driving habits to tell how greenly you're driving and how you can improve.
As aftermarket accessory manufacturers gain more experience with the OBD-II standard, we may begin to see even more innovative uses for this data. Maybe some enterprising GPS manufacturer will figure out how to use the OBD supplied vehicle speed and steering-angle information to increase tracking accuracy in urban canyons and tunnels. Whatever the next cool application of OBD tech will be, we think there's still plenty of mileage to be gotten out of this little port.