Overview OBD2 OBDII

Each year the new car designs are more computerized and more complicated than ever. What most people don't realize is that there are ways to make all this complexity work for you, rather than against you. Your vehicle's on-board computer systems contains useful info for vehicle maintenance, diagnostics / repair, performance tuning, and even driver evaluation.

Many do-it-yourself fans gave up on vehicle maintenance/diagnosis, intimidated by the complexity of newer cars. Don't let something as simple as a loose gas cap force you to spend time / money hooking up to a car dealer's overpriced diagnostic machine, just to get your Service Engine Soon light off. (see this Wired News article: Drivers Want Code To Their Car ) Or fail a state emissions test because of a loose connector, or contribute to air pollution, waste gas, and lose performance because of a malfunction that may be simple and inexpensive to repair. OBD2 can make it easier than ever to work on your own vehicle, or communicate better and have more trust when it comes to involving a professional mechanic.

Performance is about getting the most out of your vehicle, your gasoline, and your consumable parts. Remember the 'good' old days, when the majority of performance tuning involved the black art of carburetor adjustment, timing strobes, and dwell meters for adjusting points? Newer vehicles adjust fuel injection, timing, and spark constantly, providing great tuning but can often hide performance robbing problems. If a human has an adjustment all the way out, they often start looking for contributing issues, while the computer cheerfully obeys its simple instructions. Want to get the most out of an expensive, high performance air filter? Or should you just swap it out whenever the clerk or manufacturer thinks the 'average' usefulness is over. OBD2 can help you objectively measure the effectiveness of parts, to see if the expensive ones are worth it, or precisely when to change them.

Better communication with your vehicle can mean better drivers. How many people got better gas mileage when the 'instantaneous' calculated mileage showed up on the dash? Keeping track of teenage drivers, deciding which commute path used the most gas, providing data on accident circumstances, and providing feedback on driving smoothness can all be accomplished with a little help from the data usually isolated inside your vehicle.

Interested? Here are some Frequently Asked Questions (and answers) to get you started.

Which electrical OBD2 interface does my vehicle have? Although OBD2 is a standard, each manufacturer is free to implement it in their own way, so as to not stifle innovation. (I can't tell if I am being sarcastic here) If you are going to build your own converter, or buy a converter that isn't universal, you must determine which of the 3 or 4 types of OBD2 electrical interfaces is in your vehicle. Check our Tech page OBD2 electrical interfaces page for tips and help in solving what turns out to be a very tough question.
Where is the OBD2 interface in my vehicle? Usually under the driver side dash. Here is a drawing from the EPA website showing the standard positions. If you are still having trouble, check this hard to locate interface page.
What data does OBD2 provide? Theoretically, the OBD2 could provide any data that any of the sensors are capable of reporting. However, the manufacturers do not seem especially anxious to publish request codes specific to their vehicles to get this data. The OBD2 spec mandates a functional addressing mode and the request codes for about 30 parameters directly related to emissions. Support for most of these 'generic' data points is common, in both the tools and the vehicles.
What is included in the 'generic' OBD2 data? Generic data includes calculated engine load, coolant temp, data about short and long term fuel trim (whether the engine is adjusting lean or rich), fuel pressure, manifold air pressure, engine RPM, vehicle speed, ignition advance, intake air temperature, air flow, throttle position, and O2 sensor data. The ability to get/clear trouble codes, and the above data values present when the trouble code is set.
What is 'extended' OBD2 data? This includes any data that is not in the above 'generic' set. Almost every manufacturer provides many more data points that their own proprietary scantools are capable of reading.

Vehicle On-Board Diagnostics II (OBD2) Overview