Beginner’s Guide To On-Board Vehicle Diagnostics (OBD)

Technology continues to improve cars in innovative and amazing ways. But the increased use of tech also has a downside. Modern vehicle systems are more complicated than ever before. When problems occur, their cause might not be immediately apparent.

On-Board Vehicle Diagnostics monitors your vehicle’s system, alerts you to any potential issues, and helps you identify the cause. In short, it’s a valuable asset – practically a partner – in keeping your vehicle running safely and smoothly.

On-Board Diagnostic scanners can seem complicated at first, but they’re actually a relatively simple tool which just about anyone can use. Here’s everything you need to know:

What is an On-Board Vehicle Diagnostic System?

Usually abbreviated as OBD, an On-Board Vehicle Diagnostic System is a handheld tool which connects to just about any modern-day vehicle. Once connected, it interfaces with your vehicle’s computer to retrieve information about any malfunction.

Basically, the OBD allows you to “talk” to all of your vehicle’s systems. It interacts with practically all aspects of your vehicle, including the ignition system, transmission, engine, and more. 

How Does OBD Work?

Sensors are located throughout your vehicle. If they detect a problem, your Check Engine Light or another dashboard warning light will illuminate.

Of course, dashboard warning lights can be difficult to decipher. After all, the Check Engine Light only lights up; it doesn’t provide any detail about what’s wrong.

That’s where the OBD system comes in. It “talks” to your car to get a Diagnostic Trouble Code. Often referred to as a DTC, the code corresponds to a specific issue or system in the vehicle.

Sometimes the code will help you identify the issue instantly. Other times, it’ll point you in the general direction. Regardless, getting a diagnostic code (or many) is usually the most important first step in diagnosing and fixing the majority of automotive issues.     

Additionally, the OBD scanner allows you to clear the check engine light and other indicators. Sometimes, you can fix the issue, but the light will remain lit for a while. Clearing the scanner removes the codes and turns off any corresponding dashboard lights.

OBD Lights and Emission Testing

Every state regulates vehicle emission levels to help maintain clean air. Specific testing methods and standards vary based on factors including state law and vehicle type. However, an OBD scan is almost always part of the test for any cars made after 1996.

An active warning light in your vehicle means it will automatically fail an emissions test. You want to use the OBD to identify and fix any issues before the emission test.

(Of course, the vehicle can still potentially fail even if no warning lights are visible, but active warning lights are a guaranteed fail.) 

Another option is available, too. You can use the OBD to clear any warning lights without fixing the problem. Try to take the test within a few hours after clearing the lights. If you’re lucky, the lights will stay off during the test, and you’ll pass.

Of course, this isn’t the most environmentally-friendly way to maintain your car – you’ll eventually have to fix whatever’s wrong – but it can be a temporary solution if you need to pass emissions before you’re able to make repairs.  

Compatibility of OBD Scanners

Handheld OBD scanners, and the corresponding OBD inputs on vehicles, first appeared in the 1980s. However, these early models weren’t standardized. Instead, owners could only use a scanner made specifically for their vehicle’s make and model.

Obviously, this was not an ideal situation for consumers. Each auto manufacturer had a mini-monopoly with their OBD scanners. They could set the price and determine the features – and the customer had no other options.

In January 1996, the EPA forced standardization on the industry. All vehicles sold in the U.S. must adhere to a set of minimum diagnostic standards. The new scanner was dubbed OBD II or OBD2.

Once on-board vehicle diagnostics were standardized, owners could now use one code reader for all vehicles. Additionally, third-party companies could now make their own code readers with a focus on customer needs. Code readers dropped in price while increasing in quality and number of features.

Keep in mind standardization occurred in 1996. Cars made before that year will still have manufacturer-specific code readers. The input port may or may not be compatible with the OBD-II model.

The Difference between OBD and OBD-II (and Why it Doesn’t Matter Much)

The terms get a little confusing. Yes, the OBD-II is technically a different type of scanner than the original OBD. However, most people use the term “OBD” generically, even when referring to the OBD-II system. Most likely, the term “OBD” will continue to become more common as the years go on and the “original” type of OBD scanner becomes a distant memory.

Compatibility issues boil down to when your car was made. If it was manufactured after January 1996, you should have no problem using any modern scanner. However, vehicles made before 1996 often need one specific type of scanner. Check your owner’s manual for details.   

What Features are Available?

Basic models keep operations fairly simple. They scan codes and allow you to delete codes from the system (which turns off any related warning lights). Truthfully, you don’t need a ton of features beyond those standard functions. These basic models are the more affordable option.

But if you want to spend a bit more, you can find scanners packed with extra features. More complex scanners can display real-time information on engine performance plus additional diagnostic information. Advanced scanners are typically operated through a connection to a laptop.

How to Use On-Board Vehicle Diagnostics

OBD scanners are typically simple to operate with basic “plug and play” functionality. You don’t need any advanced mechanical know-how to make them work. Here’s how to use one:

Do a Basic Vehicle Check-Up

Check Engine Lights are no fun. When that light comes on, it’s easy to assume your car has a serious problem. Most people assume diagnostic procedures should be performed right away.

However, that’s not always the case. If the Check Engine Light turns on, don’t panic. The light signals a huge variety of potential issues, with an emphasis on potential.

Before attaching the OBD scanner, perform a cursory check on your vehicle for minor issues. The Check Engine Light can turn on for something as simple as an open gas cap or a wet engine. Identifying these tiny problems early on can save a ton of time and frustration.

Find the Data Link Connector

All OBD scanners made after 1996 have a 16-pin plug. It connects to the vehicle’s Data Link Connector.

Locating the vehicle’s connection point isn’t always easy. It’s usually somewhere underneath the steering wheel. When sitting in the driver’s seat, it will often be located in the general area above your knees.

Some outlets are uncovered while others have a plastic cover, which flips open. Check your owner’s manual for the exact location.

Unfortunately, the Data Link Connector isn’t always located somewhere convenient. You might have to get down on the ground to reach into the underside of the driver-side dash.

Insert the Scanner

Insert the scanner while the engine’s off. Once the scanner is in place, you’ll need to take one of two actions, depending on your scanner’s specific instructions. Some need the ignition cylinder switched to the On position while others need the entire engine on and idling.

Most scanners turn on automatically, but a few have an on/off button which needs to be pressed. 

Scan the System

Scanners are usually simple to operate. You’ll press either a Scan or Read button. After a brief moment of processing, one or more codes will display. You’ll usually be able to scroll through the codes using arrow keys. Of course, exact instructions will be in your scanner’s handbook. 

Fancier systems can have large displays with additional information and even touch screens. Simpler systems usually have a one-line LCD screen with a few buttons. Either way, basic functions remain the same. You can scan, scroll through codes, and eventually delete them.

Read the Codes

Systems with a USB port can transfer the codes to a laptop. Otherwise, you can write the codes down on a piece of paper. Most scanners won’t hold the codes for long after you’ve unplugged the scanner from the vehicle.

Look up the Codes

In the 1990s and 2000s, interpreting the codes was far more of a hassle than it is today. Back then, you had to look up the codes in a booklet which came with the scanner. Typically, it was a tiny book, jammed with information, which was annoying and inconvenient to read through.

While these booklets still exist today, most people look up the codes online. Although code meanings rarely change over time, online resources typically provide more detail (and they’re usually easier to read, too).

Note: OBD codes aren’t in most owner’s manuals.

What the Codes Mean

At first glance, the codes look like nothing but a bunch of random letters and numbers. But each character has a specific meaning.

Understanding how the codes are created can help diagnose problems. If the code itself doesn’t point to a clear cause, the individual characters can direct you towards specific systems for further investigation.

The First Character

It’s a letter, either B, C, P or U. Each signals a different category or system with the potential problem. The first character is the vaguest, most general identifier.

●        B stands for Body. It indicates problems within the passenger compartment.

●        C is for Chassis. C codes signal an issue related to the exterior of the vehicle, outside the passenger compartment.

●        P refers to the Powertrain. It indicates problems within the car’s engine compartment.

●        U is the User Network, which is all computer-related connections and features.

Indicating a problem in the engine compartment, P codes are the most common. They’re organized in groups of 100 and work in connection with the third, fourth, and fifth characters in the code. For example, P0100 to P0199 point to problems in the fuel and air metering system.

The Second Character

The second character is a digit. It’s usually either zero or one. Rarely, it can be two or three. These digits explain the type of code.

Zero is a generic code, also referred to as SAE code. SAE stands for the Society of Automotive Engineers, a professional organization which sets various diagnostic standards. SAE codes are universal across all makes and models.

The number one is a manufacturer specific code. It signals a problem specific to the make and model of your vehicle. For example, B1 is a body problem which can only occur in your type of car.

Two and three can signify either generic or manufacturer issues. These digits are rare. Usually, you’ll want to concentrate on what the other characters in the code tell you.

The Third Character

The third character can be either 0 through 9 or A through C. Numbers are used for gas and diesel-powered engines while letters are for hybrid vehicles. Here’s what each number corresponds to:

●        1. Fuel and air metering

●        2. Fuel and air metering (injector circuit)

●        3. Ignition system (including misfire)

●        4. Auxiliary emission control

●        5. Speed control and idle control

●        6. Computer output

●        7, 8, and 9. Transmission

The Fourth and Fifth Characters

The fourth and fifth characters express a number between 00 and 99. This number is the most specific guidance provided. It indicates the exact problem (or as close as possible) within the system.

The entire code gives the most precise picture of the problem. But if you’re not finding an issue in the area indicated by the code, take a broader view by checking the larger systems each character refers to.

Final Thoughts

Your car has a lot to say, and a scanner is a perfect translator. After all, diagnosing a car problem is the first step towards finding the solution.

Fortunately, OBD scanners are affordable, effective, and simple to use. The guide above will help you find the perfect choice to keep your vehicle in excellent condition.