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OBD2: A Brief Intro to Onboard Diagnostics II

OBD is a vehicle’s self-diagnosing system that gives you information on the status of your car. Read this introduction to know more about OBD2 Technology.

onboard diagnostics system components

Have you ever noticed a spot in your car that looks like something plugs in there?

If you’ve wondered what that’s for, its primary use is for OBD or On-board Diagnostic tools.

OBD is a vehicle’s self-diagnosing system that gives you information on the status of your car.

When a check engine light or a service vehicle soon light comes on in your dashboard, you should be able to use OBD to find the problem.

When a proper tool is plugged into an OBD equipped car, it communicates with the Engine Control Unit (ECU) and provides valuable troubleshooting information.

OBD has taken a few different forms over the years since its introduction in the 1980’s. Let’s take a look at how OBD has changed and how you can put the information it provides to good use.

OBDI System

Computers in cars with scanning abilities go as far back as the late 1960’s.

obd1 connector
OBD1 Connector. Source: photobucket.com

While OBD-I isn’t the first ever onboard diagnostic system in a car, it is the first widely recognized, somewhat standardized system.

It was originally intended to encourage automakers to put effective, reliable emissions systems in their vehicles. Manufacturers quickly realized it could be used for a lot more than emissions testing. The links, locations, codes, and procedures were not standardized across the industry.

On some higher-end vehicles like Cadillacs, you could read the codes right on a screen in the car so it didn’t require hooking up a special tool.

For most OBD-I equipped cars, you needed a tool that was capable of communicating with the car through its specific link.

When it was hooked up, it gave you a two digit Diagnostic Trouble Code (DTC) corresponding to a trouble indicator on the dash. This system was primitive compared to our standards today, but it was a step forward for standardized onboard diagnostics.

OBDII System

Introduced in the mid-1990s, OBD-II is the diagnostic system that is still the industry standard today.

obd2 connector
OBD2 Connector. Source: wikimedia.org

It’s far more sophisticated and standardized than OBD-I.

It gave us a universal connector that’s the same in every car sold in the US since 1996. This made it much easier for motorists and technicians to read DTC’s. Instead of needing special tools for different manufacturers, all you need now is a universal OBD2 scanner.

OBDII has a much wider range of DTC’s than OBD-I.

This allows us to find more information about what’s wrong with a car, simplifying the diagnosing and repairing process.

OBD2 trouble codes contain a letter followed by four numbers. Different letters indicate different types of issues.

  • P indicates a powertrain issue,
  • B means body,
  • C means chassis,
  • and U means there’s a network issue.

After the letter, the four digit number specifies what’s wrong with that part of the vehicle.

OBD2 Applications

There are several consumer and professional diagnostic tools that can be used to read OBD2. They range from handheld tools with a screen the size of a few digits to tools the size of large tablets that provide all of the detailed information you could ask for on your car.

1. Hand-Held Scan Tools

These are the most common OBD2 readers.

They’re the ones you’ll find the most easily available for anyone to purchase.

They’re also usually the ones that parts stores use when they give you a quick, free diagnostic scan. You can get the most basic ones that just give you your five-digit DTC or a more advanced scanner that can give you more details.

The basic ones can read just about anything except for Antilock Brake System (ABS) issues. Only the more advanced, expensive scanners can diagnose ABS problems in detail.

Top of the line models can even graph data about your car right on the screen.

2. Mobile Device-Based Tools

Mobile scanners essentially serve the same purpose as traditional handheld scanners.

The difference is you can read the information on a mobile device like a smartphone or a tablet.

These usually connect to OBD2 links via USB, but some are available with Bluetooth and Wifi transmitters for wireless connection. Just download the proper application on your device, plug in the transmitter to your car, and you’ll be ready to scan.

3. PC-Based Scan Tools

These are powerful tools for serious business.

PC-based scan tools usually use a USB interface to connect a car to a PC or Mac. This has many advantages over handheld tools like a full, easy to read display, storage for saving data, and the flexibility to use multiple software programs.

This is what you need if you’re consistently logging data.

It’s by far the easiest way to really work with OBD2 data and keep it saved in one place. These are most often used by professionals but are also available to anyone.

4. Data Loggers

Data loggers are not so much for diagnosing problems as they are for recording driving information. While they can be used for diagnosis by recording engine data under normal use, they’re becoming very popular with insurance companies.

They’re commonly used as a form of auto insurance risk selection.

Customers can sign up for a program where the insurance company sends them a data logger, the customer keeps it plugged into the car being insured, and the driving data is analyzed to assess the risk level of the driver and the car.

This is obtained by monitoring things like speed and times of day that the car is driven.

Some are even equipped with built-in accelerometers to measure how hard the driver brakes. After it’s plugged in for the specified period of time, the data logger is sent back to the insurance company.

Depending on the data that’s logged, drivers can be eligible for insurance discounts.

5. Emission Testing

Emission testing and maintenance is one of the original purposes of onboard vehicle diagnostics.

OBD2 is an easier, more convenient way to test emissions rather than at the tailpipe. Many states with mandatory emissions testing have switched to OBD2. All OBD-II equipped vehicles have codes to indicate issues with the emissions system and can easily confirm if it’s in compliance with emissions laws.

This is a great example of modern technology benefiting the environment.


Onboard Diagnostics have been a big step forward for cars.

It’s easier than ever to troubleshoot and diagnose problems with cars, trucks, and SUV’s.

Rather than clumsy, sometimes inaccurate mechanical tests to find problems, it’s much easier, cheaper, more accurate, and safer to just plug a scanner into the car and let it tell you what’s wrong.

It’s also helping keep cars emitting clean emissions and even giving good drivers insurance discounts. OBD has made life easier for motorists and technicians alike.

Which OBD2 application is the most useful for you?

Read More: Which OBD2 Protocol is Supported By My Vehicle?

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Tim MillerFounderOBD Advisor

I’m Tim Miller from Denver, Colorado. I’m the founder of obdadvisor.com, an automotive blog about "Diagnostic Tools and Auto Repair". My fan page is facebook.com/autozikcom. I've been working as an automotive mechanic and blogger for over 10 years writing articles to share my experiences and expertise.

Web: https://www.obdadvisor.comEmail: [email protected]
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2 thoughts on “OBD2: A Brief Intro to Onboard Diagnostics II”

  1. Bonjour,
    J’ai recu un kw850 , sans sont CD …
    Chez qui je peux ne le procurer ??
    Merci et bonne journée.

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