What Is The OBD-II Port And What Is It Used For?
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If you purchased a car after 1996, chances are it has an OBD-II (On-board diagnostics II) port. Every car or truck on the road manufactured after that point is mandated by United States Federal Law to have one installed. But what is it?

OBD-II is a sort of computer which monitors emissions, mileage, speed, and other useful data. OBD-II is connected to the Check Engine light, which illuminates when the system detects a problem.

Depending on the problem, the light either stays on, flashes, or goes away entirely. Mechanics can use scan tools to make sense of the diagnostic trouble codes, but with the right equipment and some technical know-how Learn To Diagnose And Fix Your Own Car With These 10 Excellent Websites Learn To Diagnose And Fix Your Own Car With These 10 Excellent Websites These days, cars are computers on wheels, but you can still teach yourself to catch fault cues and diagnose problems before you park it in the garage. These ten websites may not make you a... Read More , you can too. You can even collect data on other aspects of your vehicle’s performance.

A Look At OBD


Onboard Diagnostics refers to any vehicle’s ability to register and report issues that may occur, or have occurred within the system. One of its strengths is it can detect problems long before the driver is able to notice any symptoms, such as low-performance, low-fuel economy, and heavy emissions, or before the Check Engine or Malfunction light comes on.

As you would expect, OBD-II is heavily used by professional mechanics, but there are consumer oriented products that can take advantage of its diagnostic abilities.

OBD was first introduced in response to a ruling by CARB (California Air Resources Board) that all vehicles under 14,000 lbs sold in California be equipped with on-board diagnostic systems. As a result most cars and trucks on the road today have this functionality enabled.

While there are eight total standard interfaces, for now, we’re just going to focus on what lead to OBD-II.



Before OBD-I, each manufacturer had their own set of standards for OBD, meaning that mechanics had to buy expensive scan tools for each manufacturer. OBD-I was first introduced in 1987, and standardized onboard diagnostics.

It had sensors that detected emissions and was able to minimize them by releasing emissions-controlling valves. However, it had many problems and shortfalls.

As a result, it was mandated in 1996 that car manufacturers equip cars and trucks with OBD-II ports. While every system is the same, for the most part, the systems may vary slightly. These are known as protocols. There are five basic signal protocols in use – SAE J1850 PWM, SAE J1850 VPW, ISO9141-2, ISO14230-4 (KWP2000), and ISO 15765-4/SAE J2480 (CAN-BUS).

How do you know which protocol is used for your vehicle? Well, as a rule of thumb, General Motors cars and light trucks use SAE J1850 VPW. Chrysler cars and trucks, all European imports, and most Asian imports use either ISO 9141 or KWP 2000. Fords before 2003 use SAE, and all vehicles manufactured after 2008 use CAN. Because CAN has become the new standard, all vehicles will adopt this in the future.

OBD-II’s primary method of alerting the driver to any problems with the vehicle’s performance is via the Check Engine light. When this comes on, there’s the potential for serious damage to your vehicle, and drivers are recommended to take their car to a mechanic immediately.

How Does It Work?

Diagnostic Trouble Codes (DTC) are stored in the system. The codes are not necessarily the same across all vehicles, and it is not uncommon for foreign manufacturers to use manufacturer specific codes. Aside from that, however, a mechanic (or anyone with an OBD-II scan tool) can connect to the port, read the DTC, and identify the problem (or problems) with the vehicle.

For example, error codes P0001 to P0099are Fuel and Air Metering and Auxiliary Emission Controls issues, and P0700-P0899 are Transmission issues.

The Port


The port, also known as the SAE J1962 diagnostic connector, is either white or black, and is usually located behind the dashboard, above the brake pedal. It has spaces available for sixteen pins, but it may not actually have sixteen pins. Pin locations vary depending on the signal protocol supported by the vehicle.

As mandated by United States federal law, the port must be easily reached by the driver. The port allows for a scan tool, or anything else compatible with OBD-II, to be plugged in, and information can be then gained about the vehicle.

What Can Be Hooked Up To The Port?


Traditionally, hand held scan tools are hooked up, allowing the average vehicle owner to read DTC’s. However, a reference for the code numbers is still needed. You can find such a reference in various handbooks and websites, such as OBD-Codes.

Some modern scan tools can be connected to a Windows desktop or laptop OBD2 & Windows: Save On Auto Repair With Diagnostic Tools OBD2 & Windows: Save On Auto Repair With Diagnostic Tools Finding a broken car's fault can be costly. Save by doing it yourself! All you need is a Windows computer, free diagnosis software, and a cable plugged into your car's OBD II connector. Read More , like ScanTool’s OBDLink SX USB Adapter on Amazon for $29.95, which allows you to turn your laptop into a very detailed scan tool. There is also ScanTool’s 427201 OBDLink LX Bluetooth, which allows a phone or tablet to connect via Bluetooth, that you can also find on Amazon for $59.45. While it is compatible with apps like Torque and DashCommand, it is not compatible with iOS devices. With this, you can turn your phone or tablet into a handy little scan tool that displays detailed information about your vehicle.

Besides just reading diagnostic codes, there are other scan tools on the market which offer features aimed at average customers, like this BigBanana BB700 Auto Scanner. Not only is it a diagnostic scan tool, it allows you to keep track of data parameters in real time, like rpm, miles per gallon, and speed. It is a little more complex than the average scan tool, hence the hefty price tag of $93.99.

Finally, you can use many Android and some iOS apps to monitor your car’s performance via the OBD-II port. DashCommand for both Android and iOS, made by Palmer Performance Engineering, Inc. turns your phone or tablet into an incredibly advanced display for your engine data.

Android Screenshot 1

DashCommand also allows you to check specific areas of your vehicle’s performance like your miles per gallon and emissions, and includes an inclinometer. Finally, you can check the diagnostic codes that correspond with any problem OBD detects within the vehicle. It goes for $9.99 in the iOS store, but is free in the Google Play store.

Android screenshot 2

For Android, there are apps like>Torque Pro, which uses GPS to create travel logs with OBD engine logging that shows you what you were doing at any given point in time, whether you were driving, stopped, or breaking. It also allows you to view stats like your CO2 emissions, if you are trying to be eco-friendly. It is available through the Google Play store for $4.95. These apps allow you to view your performance as you drive How To Monitor Your Car's Performance With Android How To Monitor Your Car's Performance With Android Monitoring tons of information about your car is incredibly easy and cheap with your Android device -- learn about it here! Read More , before problems develop.

Engine Link by K Solution LLC allows you to turn your iPhone or iPad into a vehicle/car performance/diagnostics tool and scanner. It works a lot like Torque Pro in that you can track your car’s parameters in real time and view them in an easy-to-read graph. However, it requires an OBD-II WiFi adapter or a Bluetooth adapter that connects to the OBD-II port, like the ieGeek® WIFI OBD2 Auto Scanner Adapter Scan Tool for your iOS device. You can find the app in the iOS store for $5.99.



Are you a driver who wants to be more aware of what’s going on in your engine? Perhaps give some of these apps and scan tools a try and let us know what you think!

Image Credits: Autocom CDP Pro for Cars via Flickr, Female OBD-II Connector on a Car via Wikipedia, Citroen DS5 via FLickr, Engine via Flickr, On [46 of 52] via Flickr.

Explore more about: Automotive Technology, OBD-II.

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  1. Josh Veach
    June 4, 2016 at 11:17 pm

    Is there an obd 2 tool software that I can load on windows 10 and use my ObdSX or MX Bluetooth tool with that allow me to turn features on and off like shutting off air bag, turning GM's AFM off "8cyl to 4cyl mode" or boost the idle rev limit because I have about 20 2001 to 2015 GM, Fords, and a few MOPAR that sit and idle on the job site for hours and hours and its hard on them and easier if you up the rev limiter I heard.

  2. Teri
    May 26, 2016 at 6:55 pm

    can I plug in my battery maintainer through the OBDII port? It comes with a 12V plug adapter but the power cuts off to that when I turn off the vehicle.

    Also, could I plug in a portable power bank into the OBDII and use it as a memory saver for when my battery gets disconnected? I heard it could be used for that but I'm worried too much power going into the port could hurt something.

  3. esraa elkholy
    December 11, 2015 at 12:28 pm

    i just want to know if i used Can bus shield with obd2 port cable for my KIA Car , what will be the sample output from the port of the can bus ?
    Is it 1's and 0's or i should display it on a certain software to get the output sample readable for me ?
    is it accessible to show me the output from the can bus if i connected it to a machine link or a raspberry pi?
    what will be the output , is it voltages or signal bits, is it a hexadecimal indication ?
    thanks in advance

  4. John
    December 1, 2015 at 4:47 am

    Can this tell you things like, why the interior lights are not working? And if any relays or fuses are gone in a car?

  5. Scott M.
    January 3, 2015 at 2:59 am

    The following are good places to get more information on different products. Shopping at retailers like Amazon might not give you details and info about available options. I've purchased a ScanGauge II for my brother and OBD-II reader from ScanTool that I use with an old 7" Asus eeePC. PLX Devices also make OBD-II readers for Android and iOS as well as a stand-alone unit. The PLX Kiwi and the ScanGauge II are small stand-alone units that can be mounted in the vehicle for those that don't have an Android or iOS device, or want to monitor engine sensors (temperature, voltage, etc) or fuel economy.

  6. horribilis
    December 31, 2014 at 8:11 pm

    I've always wondered how those work! I couldn't have asked for a more cogent explanation. Thanks for helping me educate myself.

    • Taylor
      January 4, 2015 at 7:49 pm

      You're absolutely welcome. Thank you for reading and commenting. :)

  7. Doc
    December 31, 2014 at 12:16 am

    "...focus on what lead to OBD-II." I think you meant "led," not "lead." :)

    • Taylor
      January 4, 2015 at 7:53 pm

      You are absolutely right. Sorry about that.

    • Taylor
      January 4, 2015 at 7:52 pm

      Wow! A shame it doesn't seem like it's iOS compatible though. It doesn't seem like many bluetooth scanners are.

  8. jshal
    December 30, 2014 at 2:58 pm

    Did you mean "braking...?"

    • Taylor
      January 4, 2015 at 7:52 pm

      Yes I did, sorry about that. :)