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OBD2 Codes: What You Need to Know

OBD2 Codes are part of the car self-diagnostic system to signal where the malfunction may come from. It’s also referred to as Check Engine Light Codes and Diagnostic Trouble Codes(DTC Codes). It’s essential for mechanics and drivers who would love to know what happened with their vehicles.

Even if you don’t really want to be a mechanic or handle your vehicle issues alone, knowing the OBD2 codes will help you save the time and money for a car diagnostics when you see a check engine light, as well as equip you with primary knowledge before you go to the mechanics (to avoid mechanic scams). Actually, most check engine lights could be fixed by really simple fixes at a low cost, and we highly recommend you to read OBD2 codes for the lights rather than ignore it. 

In this article, we will tell you what OBD2 codes are, how to read, and interpret them. Knowing more about OBD2 codes will help you understand your vehicle better, driver safer, and save money.


What are OBD2 Codes?

OBD2, the abbreviation of On-Board Diagnostic, is the self-diagnostic system of all vehicles. All vehicles are equipped with a computer, Powertrain Control Module, which conducts regular self-check to make sure that the vehicle is in good condition. When it diagnoses a problem, a Diagnostic Trouble Codes(DTC Codes), AKA OBD2 Codes will be generated and then turn on the check engine light. They indicate what the malfunction might be and help car diagnostics.

obd2 codes


What’s the difference between OBDI and OBDII?

OBD was introduced in the early 1980s with a simple function to turn on the check engine light when a malfunction was detected. Back then, different automotive manufacturers had different diagnostic signals and the reading of trouble codes was really difficult, as mechanics had to equip themselves with different tools to read the codes for different car makes. 

In 1996, an improved version of OBD, OBD2, was introduced and made mandatory for all cars sold in the United States. OBD2 regulates all vehicle manufacturers to design a standard OBD port and follow a specific messaging format of the codes with standard meaning for each code. That was when the OBD2 became popular on the market as it can be used to diagnose malfunctions for all vehicles and provide a standard result that will help identify the problem.


How to Read OBD2 Codes?

Step 1: Select an OBD2 scanner

To read the OBD2 codes, you need a tool called OBD2 Scanner, AKA Car Code Reader. There are many different types of OBD2 scanners on the market, and you may find it difficult to choose the right one without primary knowledge. 

The major types of OBD2 Scanners are traditional wired OBD2 scanner, Bluetooth OBD2 scanner, smart OBD2 scanner/monitors, semi-pro scanners with car fixing guides, and professional tools used by mechanical engineers. You can also pick a cheap elm327 and pair with Torque app, which is a widely used cost-effective combination of reading OBD2 Codes. For more information about how to buy a suitable OBD2 scanner, please check the complete buying guide below.

Recommended Reading: Best OBD2 Scanners Complete Buying Guide

Step 2: Plug the scanner into the OBD2 port

When you get the scanner, plug the scanner into the OBD2 port in your vehicle. It’s usually located under the dashboard, beneath the steering wheel column(1-3 in the diagram). If you cannot find it, try searching for it in the areas indicated by numbers 4-9. Plug the scanner in when you find it.

OBD2 port


Step 3: Read the OBD2 codes

After plugging in the OBD2 Scanner, you can start reading the OBDii codes. Here’s when the tools will make a difference:

  1. Wired Tools: For some simple wired, hand-held scanners, just hit the “scan” button on the tool and a list of codes will appear. Note down the codes presented and search for the code meaning online. Remember to write down the codes and keep a record for future diagnostics. 

  2. Bluetooth Tools: For Bluetooth OBD2 Scanners, you will have to pair the device with a mobile APP. After plugging in the OBD2 scanner, download a mobile app, turn on the Bluetooth of your phone, and pair them together. After pairing the OBD2 Scanner and the mobile app, follow the instructions and run the scan. It will also generate a list of car codes, and some apps will keep a record for you and some even show the details of each code for your convenience.

obd2 scanners

Some Bluetooth OBD2 Scanners have a bundled APP developed by the same company, and some are just a cheap elm327 chip and you have to find an app that’s compatible with it. We recommend a tool that has an app developed by the same company for better compatibility and customer services. Some even have additional features on the APP.

Recommended Campaign: ZUS Smart OBD2 Scanner FREE GIVEAWAY


How to Interpret OBD2 Codes?

Now you have the OBD2 Scanners ready and got one or a list of Diagnostic Trouble Codes. And the next question comes: what do they mean?

The OBD2 codes consist of a five-digit alphanumeric code following the messaging format below:

OBD2 Codes

The first letter(PBCU) indicates where the problem is from, the second number(0, 1) indicates whether it’s a generic or manufacturer special code, the third one indicates the specific malfunctioning part, and the last is used for special fault index. Indicated by the first letter, there are four basic categories of OBD2 Codes:

  • P for Powertrain which means the engine, transmission, emissions, and ignition to name a few. The codes associated with P is the largest set of codes. 
  • B for Body includes items such as power seating and airbags.
  • C for Chassis which covers the anti-lock braking system (or ABS), axles, and brake fluid.
  • U for Undefined, meaning that any other aspect of the car is going to be found in this system.

There are more than 3k generic OBD codes. If you dig into the details of your driver’s manual, you will find a full list of Car Codes specific for your car make. But don’t worry, you don’t have to remember what they mean. All you have to do is to search for the code online or just read the explanations on the OBD tool/app. 

Related Resource: Search for the Code Explanations


How to Fix OBD2 Codes?

You are now equipped with OBD2 diagnostic knowledge, and it is obvious that they are not some mystery puzzles to interpret. The next question is: Would it be possible to fix these OBD2 codes by yourself at home? The answer is YES! 

nonda's Smart Vehicle Health Monitor can monitor your vehicle health and read all the OBD2 codes. Pairing it up with the ZUS app, you can get full diagnostics of your codes as well as a dedicated short video to teach you how to fix them at home. Check out the video below and see how it can help you save thousands of dollars on car expenses:

How to Fix P0420 Engine Code in 3 Minutes [3 DIY Methods / Only $4.97]


More videos of troubleshooting DTC codes:

P0171 - System Too Lean (Bank 1)

P0456 - EVAP Control System Leak Detected (Very Small Leak) 

P0300 - Cylinder Misfire Detected, Random/Multiple Cylinder 

P0400 - Exhaust Gas Recirculation (EGR) Flow Malfunction

P0128 - Coolant Thermostat Malfunction

All videos are produced by nonda Auto DIY Center. Check out their YouTube channel to learn more about DTC codes. 



Reading and interpreting OBD2 Codes is simple and it helps you to understand your vehicle better, drive safer, and save money. You can do a car diagnostic test by yourself, which usually takes you several hours and costs you $40-$400. Even if you found that you cannot fix it after simple diagnostics following the guides online, knowing the issues will prevent you from being scammed by mechanics.


An Easy Step: Try the ZUS OBD2 Scanner for FREE

Although reading OBD2 codes is simple, investing in an expensive OBD2 scanner might be risky, especially when you are new to car checks and fixing. Here we would love to recommend our ZUS OBD2 Scanner to you! 


  • Reads the OBD2 codes and shows explanations
  • Easy to install and use
  • Monitors your vehicle health
  • Records the codes and issues detected for history checks
  • Useful additional features such as mileage tracking and car finder
  • FREE device with FREE APP on both Android and IOS!

We are now on a campaign of FREE GIVEAWAY, and please feel free to check it out below! Don’t miss it!

car code reader

Hope this article is helpful! Feel free to give feedback and we would love to add more content to help more people.

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