What is OBD-II?

OBD stands for on-board diagnostics, and OBD-II is a collection of connection and protocol standards for all cars sold since 1996, but what does it do and what can it do for you?

OBD technology was born out of the US Environmental Protection Agency's (EPA) and California Air Resources Board's (CARB) mandates that vehicles be 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 centres. Thus, the OBD standard (and the subsequent OBD-II revision) was born.

OBD-II port

On our Toyota Corolla, the OBD-II is lurking right next to the bonnet release.
(Credit: Derek Fung/CNET Australia)

The first part of the OBD-II standard is the connector (see image above). The 16-pin female interface connector must be located in the vehicle's cabin within about 60cm of the steering wheel. For most cars, this means that the connector is 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 utilised and the data isn't always sent over those pins in exactly the same manner, so there is some variation within the standard.

For instance, in the US there are five major signalling protocols for vehicles built 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, making the OBD-II standard decidedly more, uhh, standard now.

Outside of the US OBD-II standard there are also the European OBD (EOBD) and EOBD2 varieties, as well as the Japanese OBD (JOBD) standard.

What does it do?

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, not to mention the state of the vehicle's various oxygen sensors. If there is an error with any of these parameters or if a value falls outside of a pre-determined safe range, the vehicle will illuminate its Check Engine light (below).

Check engine light

It's best to know what you're checking your engine for. Enter OBD-II and its PID codes.
(Credit: Derek Fung/CNET Australia)

The vehicle's computer is able to send all of this diagnostic information — in the form of PID and trouble codes, that are essentially special PIDs — over the OBD-II connection to a connected diagnostic tool. 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 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 the airbag or tyre pressure monitoring systems, further extending the utility of the connection for dealers and authorised service centres. These non-standard PIDs are often not supported by third-party OBD-II tools, but don't impede their functionality either.

Actron PocketScan

Actron PocketScan reads OBD-II PID codes.
(Credit: Actron)

Handheld scanning 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 can be connected to the OBD-II port, recording and displaying 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 petrol 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.

CarChip Pro

The CarChip Pro can monitor how the kids/employees are treating your car.
(Credit: Davis)

Data loggers

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 screen-less 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, say, the last week. 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 110km/h 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.

PLX Kiwi

The PLX Kiwi's driving games could improve your fuel economy.
(Credit: CNET)

Fuel economy meters

With more attention being paid to maximising fuel economy, we've been seeing more and more 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 accurately extrapolate estimates. However, some vehicles 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 figures. Others will display eco lights or graphics to coach drivers towards improving the litres per 100km they extract from their cars. Some devices, such as the PLX Kiwi, offer driving challenges to help train the user to be a more efficient driver.

Bully Dog GT

Measure your car's performance with the Bully Dog GT.
(Credit: Bully Dog)

Performance computers

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 as aftermarket fuel economy meters can extrapolate litres per 100km, OBD-II-connected performance computers can estimate a car's power and torque output, time 0-100km/h runs or provide a virtual tachometer for vehicles that weren't equipped with a tacho out of the factory.

Vehicle specific devices can even be set to parse the non-standard PIDs to derive data such as turbo boost pressure or engine load.


Track and monitor your car with DevToaster's Rev app.
(Credit: DevToaster)

Future applications

Like most data-driven technologies, such as GPS navigation and mobile phone 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 Kiwi 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 EcoRoute HD system, which pulls OBD data from a Bluetooth dongle to more accurately measure your fuel economy and driving habits to tell you 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.

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BrinkleyC posted a comment   
United Kingdom

For example, newer OBD-II scanners and readers are starting to integrate Wi-Fi technology to www.obdii.co.uk wirelessly connect to a nearby laptop or smartphone for easier monitoring of a vehicle in a garage or on the road


BrinkleyC posted a reply   
United Kingdom



WenlongC posted a comment   
United Kingdom

OBDii.co.uk is a professional manufacturer of car diagnostic tools company, we provide the lowest prices of European cars, Asian cars, American cars, Mercedes-Benz, BMW, Ford and other diagnostic tools, We also supply some the universal diagnostic tool,these tools is used to for All makes, and very suitable for those auto repair technicians in the workshop, our automotive diagnostic products for the use of guidance documents and video, and we have a comprehensive after-sale systems, 7 * 24 hours online customer service, we offer a variety of automotive diagnostic software and free updates for you to solve your worries.


Ralliart posted a comment   

Owners of Mitsubishi Lancer Evolution's should check out an application called Evoscan.


2sweet posted a comment   

5 minutes ago, I had zero clue about this topic. I now feel 'nicely introduced' and now have the knowledge to consider future purchases involving this seemingly useful technolgy. Nice one Antuan & cnet.

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