You’re on the road, driving as usual when suddenly, your Check Engine Light starts shining. What’s going on? You didn’t do anything different than you normally do, so it’s probably a bug of some sort. Besides, the car is still running well, so it’s undoubtedly going to turn itself off soon. And it does, except after a short while, it turns itself on again. Now you have a Check Engine Light flashing before your eyes, making you frustrated and downright scared as something is clearly wrong.
To avoid spiraling into a panic attack when something like this happens, take a few moments to prepare yourself with a little bit of automotive knowledge. In this article, we’ll teach you how to access and understand your vehicle’s OBD-II codes as well as what to do when your dashboard starts shining.
Spoiler: there’s nothing to worry about. While older cars (pre-1996) needed various specialized tools and gadgets along with quite a bit of guesswork in order to figure out what was wrong with the engine, newer vehicles can tell you how they’re operating and what is wrong in a matter of few minutes –all thanks to the OBD-II.
What is OBD-II and How Does It Work?
Before we delve into the topic of accessing and understanding your car’s OBD-II codes, let’s first cover the basics. What is OBD-II?
OBD is short for On-Board Diagnostics and it refers to a vehicle’s capability to self-diagnose and self-report. In 1991, the California Air Resources Board required that all new vehicles sold in this state have a basic OBD capability. This is now referred to as OBD-I, because five years later, a second OBD generation was implemented for all cars manufactured in the U.S. That year, in 1996, a standard connector and communication protocol was established for all automakers.
So how did this affect car owners and mechanics back then? Positively, highly positively. The OBD-II has provided a simple means to inspect a car without using a dozen specialized tools. And we’re not only talking about potential issues with the engine – this system can also report other data, including vehicle speed, brake position, throttle position and so on.
But how does it work? On most modern cars, the fuel injection, ignition system and automatic transmission are run by a few computers which monitor various sensors located in the engine and other systems inside the vehicle. When the sensors “sense” that something’s amiss, they trigger a Diagnostic Trouble Code, also known as DTC. So, when the OBD-II detects a DTC, a Check Engine Light starts shining on the dashboard. To put it simply, the OBD-II is a built-in, standardized system that monitors all of the diagnostics in the car.
You’ve seen the DTC mentioned. This term is important because thanks to DTCs, your OBD-II can tell you exactly what’s wrong with the vehicle. How? It’s actually quite simple – DTC is a string of letters and numbers which represent specific things within the vehicle, including the engine, emissions controls, and so on. However, without a reference, these codes are incomprehensible. Luckily, there is a handy little thing called an OBD reader/scanner that not only reads these codes but sometimes offers their definitions too (not all OBD-II tools offer DTC definitions though).
How to Use an OBD Scanner/Reader
With an OBD reader or a scanner, you’ll be able to access your car’s OBD-II codes, but may not be able to understand them as this depends on the model you own. If your OBD tool doesn’t offer DTC definitions, don’t fret – we’ll cover everything you need to know right here. But first, let us say that there are hundreds of different codes, so it’s impossible, not to mention unnecessary, to learn all of their definitions. However, tackling basic diagnostics is really no big deal, especially if you’re willing to spend some time researching and highlighting important things. By the way, we made the research step super-easy for you, so all that’s left is to sit back, relax, read and write down whatever seems important to you and your vehicle.
Plug in the OBD Reader/Scan Tool
The OBD-II uses a 16-pin connector (female), also known as SAE J1962 diagnostic connector, located under the driver’s side of the dash, near the pedals. To communicate with it, you’ll use an OBD II reader/scan tool (male) by plugging it into the connector. Once you plug the OBD-II tool in, turn the ignition on but don’t start the engine – the tool will power up and start communicating with the computers in your car.
If you’d like to know more about OBD-II readers/scanners, there’s a detailed description of different types of these tools near the end of this article, so make sure you check it out.
Tip: Every scan tool is different, so once it powers up, you may see messages like “establishing data transmission link” or “searching for protocol” or something similar. In any case, a message should pop up to let you know the scan tool has successfully connected to the OBD-II port. If nothing shows up and the screen doesn’t light up, try jiggling the scanner or connector to get better contact.
Get the Codes
Once properly connected, the OBD reader/scan tool may require you to enter your vehicle information. Some models will need you to input your vehicle identification number (VIN for short), make and model, while others will not. Again, because every scan tool is different, the instructions on how to operate it will vary. In any case, there should be a menu with a submenu called “Read Codes, or “Trouble Codes” which you should select. Depending on the model of your OBD reader, there may be a few systems within the submenu Codes, such as Engine, Brakes, Transmission, Airbag, and so on. When you select one of those, you will see one type or two types of codes – Active and Pending codes. The former ones are simply live codes, in other words, certain faulty functions that are keeping your Check Engine Light on. The latter ones are a result of your OBD-II monitoring system failing to properly take out the operation of an emission control system at least once. If it fails again, the faulty function will become an Active code and your Check Engine Light will therefore turn on.
If you’re going to ask an expert to take a look at the codes (highly recommend this!), now is the time to write them down. What’s important here is to write the codes down in the same order as they appear on the reader. Some modern OBD scanners can be connected to a laptop, phone or tablet, which allows you to turn your computer/gadget into a detailed scan tool. However, these gizmos are more expensive than basic OBD-II readers.
Read the Codes
As mentioned, there are hundreds of codes so trying to memorize and understand each and every one of them is pointless. However, when it comes to the basics of the OBD-II system and DTCs, it pays to understand them. Why? For one, you’ll become more familiar with your own vehicle; two, you won’t be fooled by “experts” trying to sell you brand new auto parts that you may not actually need. If you think auto parts stores are above this – think again. There are thousands of people getting tricked into purchasing things their vehicles don’t really need, all thanks to certain experts interpreting OBD codes as “need to replace this part with a new one”. In reality, many DTCs can be solved by fixing the problem in one way or another, not by replacing the problematic part, although there certainly are times when replacement is needed as well.
Saying that, when your Check Engine Light starts shining, the best course of action is still to go to your local auto parts store to get the DTCs read. The key is to let the guy only read the codes, not talk you into buying new parts. After you’re certain of the codes, you can look up the meaning as well as common causes of those particular DTCs right here, on our website. Then, and only then, replace the parts if they need to be replaced (a good, trusty mechanic will let you know if this is necessary).
Understand the Codes
Alright, we’re finally onto the juicy stuff – understanding those OBD-II codes. While DTCs may seem impossibly complex, it’s important to remember that underneath all those letters and numbers is usually a very simple meaning. Say you get a code P0303; how to make sense of it? To make things simpler, we’re first going to break down the code into four different sections:
- This is the first character, a letter.
- This is the second character, a single number from 0 to3.
- This is the third character, again a single number, but from 0 to 9.
- This is the last section, a character that includes a pair of numbers, from 00 to 99.
Another important thing about DTCs is the difference between generic codes (also known as the Society of Automotive Engineers, or SAE) and manufacturer-specific codes. The generic ones usually start with P0xxx and they’re easy to find and understand. The manufacturer-specific codes, on the other hand, usually start with P1xxx and are harder to find as not all manufacturers want to share information about their vehicles publicly. In any case, let’s make sense of those letters and numbers.
Letters (the first section) identify the type of the malfunction:
- Pxxxx for Powertrain (engine transmission)
- Bxxxx for Body (also A/C and airbag)
- Uxxxx for User network (UART/wiring bus)
- Cxxxx for Chassis (also ABS)
A single number from 0 to 3 (the second section) shows whether the code is manufacturer-specific or not:
- X0xxx and X2xxx for generic code or government-required code
- X1xxx for manufacturer-specific code
A single number from 0 to 9 (the third section) shows what system the code refers to:
- Xx1xx and xx2xx for fuel and air measurements
- Xx3xx for ignition system (misfire)
- Xx4xx for emissions system
- Xx5xx for speed/idle system
- Xx6xx for computer system
- Xx7xx and xx8xx for transmission
- Xx9xx for input/output controls
A pair of numbers from 00 to 99 (the fourth section) shows the specific failure code and are based on the systems defined in the third character.
For example, that P0303 code? It’s a misfire condition. In other words, there’s a misfire on a respective cylinder in the firing order, in this case, misfire cylinder 3. If you see this DTC, you should get your car fixed as soon as possible ss driving in this condition can damage the catalytic converter.
If you want to read the description for your specific DTC, the OBD-Codes is a good place to start.
OBD-II reader vs. OBD-II scanner
You’ve seen us use the OBD scanner/reader interchangeably throughout this article because these are very similar gadgets. Both are connected the same way to the OBD-II port and both read DTCs. The difference is that one of these tools a simple, pretty basic and inexpensive gizmo, while the other one is more sophisticated and therefore more expensive tool. Can you guess which is which?
- The OBD-II Code Readers
Simple and easy to use, the code readers only read the DTCs but don’t offer any definition. This means that if you choose to use this tool, you’ll only see the codes displayed on the screen and nothing else, meaning you’ll have to write them down in the specific order they show up on the screen in order to ask a professional what the problem is. The code readers are the most common OBD-II tools as they’re cheap and usually more than enough for most drivers.
- The OBD-II Scan Tools
These tools come preloaded with definitions for DTCs, so with them, you not only get the codes themselves, but their meanings too. These gadgets may also provide access to manufacturer-specific codes which are usually hard to come by. Scanners also have other useful features including customizable access to live and recorded data and some can also be connected to a computer/phone for easier access.
So which OBD-II tool you need? Generally speaking, if you’re not an auto enthusiast and want only the basics so an expert can fix the problem as soon as possible, get a regular OBD-II reader. Sure, this is a rather limited-in-functions tool, but it’s enough for most folks on a budget. If you like having most of code definitions right at your fingertips, as well as lots of other features and a wealth of information, definitely go for scan tools. However, in this case, be prepared to spend money as scanners are more expensive than readers, especially the high-end types.
Besides letting you know why your Check Engine Light keeps shining, an OBD-II port can also provide you with various measurements and data parameters about your vehicle. That is, if you connect a proper tool scanner to the OBD-II connector. Nowadays, companies offer drivers ways to really get to know their vehicles and their own driving habits. How? By using special kinds of OBD-II devices – dongles.
By plugging a dongle in the OBD-II port, you can learn various things about your car or truck, including data such as rpm, speed, miles per gallon and so on. You can also monitor your vehicle’s performance via the OBD-II port and of course smartphone apps. Things like emissions and travel logs can also be obtained, with the latter one being especially helpful for parents of teenage drivers. For example, an app on your smartphone or tablet can let you know what the car was doing at any given point in time, including where it was driven, where it stopped, how it braked, etc. There are even speed-alert features which can tell you when your kid is going overboard!
Some insurance companies also use OBD-II dongles. They issue these convenient gizmos to their customers so they can achieve discounts in cases of low-risk driving habits. By using data pulled from the vehicle’s OBD-II connection, a company can look at people’s driving behavior, including their usual speed, how quickly they brake, how many miles the vehicle has been driven and so on.
While this sounds like a great idea to achieve various discounts, it’s wise to be cautious when sharing personal information with other people. Some companies will tell you they only use dongles to track your speed and number of miles driven, but in reality, the device will pick up on whatever information about your car is available, which the company then uses to determine whether or not you’re a good driver. The good news is, if you don’t want to share your driving habits with an insurance company, you don’t have to. Tracking devices and programs (which is what OBD-II dongles are if used in this manner) are opt-in, meaning an insurance company will never require you to use one to get auto insurance coverage. However, if you‘re absolutely sure of your low-risk driving habits and you’d like an opportunity to save some money, do consider giving OBD-II dongles a try.
These links will provide more detailed insights into what code means in your vehicle:
Be sure to also read our essential guide to the best OBD2 Scanner.