How to Use OBD2 Scanner & Understand It: A Beginner’s Guide

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OBD2 scanner showing a graph of its reading

You've probably heard of the term OBD2 scanner as a diagnostic tool, but have you ever used one? The OBD2 or Onboard Diagnostics tool could save your life or keep you from getting stranded on a busy highway. It interprets Check Engine Light alerts and can diagnose problems with your powertrain control module, or PCM for short.

The downside is that it works with vintage vehicles and those older than 1996 models.  This blog post will discuss how to use OBD2 Scanner and understand its readings, including information about engine codes and other essential things to know when using one of these scanners for your car.

To use an OBD2 scanner, connect your scanner to the data link connector on your car, input the car's information found on your car's instruction manual, if prompted, then scan your vehicle. 

Types of OBD2 Scanners

Code readers

Modern vehicles have a standardized system for diagnosing errors in the car's engine. The OBD2 code reader can perform these checks and can help you resolve vehicle problems in-house. It costs within the range you usually spend in having a professional mechanic diagnose your car, only that you can use it multiple times. 

However, this device comes with limited access to information on manufacturer code and other similar data. If you don't have previous experience using it or are unfamiliar with trouble codes, you may need independent input to get the information you need.  

Scan tools

If you buy the code reader, it will only allow you to clear codes and read codes. The scan tool is far more advanced; not only can they clear any stored trouble codes but also view live data too. These tools offer lightweight design and connection to an app on your smartphone, for example. 

This combination gives vehicle owners a better idea of what's going on under the hood. These scanners can monitor engine conditions such as fuel pressure - a vital component that many people give little attention to when it comes to their car or truck maintenance.     

While they are slightly pricier than OBD2 readers, this is often worth investing in if you care about maintaining your vehicle correctly. The advantage of these tools is their ability to tell you the trouble with your car in plain English rather than in codes, on the scanner itself, or using their companion app.

How to Use Your OBD2 Scanner

a car dashboard showing the check engine light on the tachometer

All vehicles standardized by OBD2 systems connect with an SAE J-1962 connector that matches those already on board. The SAE J-1962 connector is a universal type of connector that you can use across different models. The scanner will start reading information after connecting its cable to an unused port under the dashboard of most vehicles.

The scan tool might also have module functions for accessing specific data like airbag codes or ABS brake system faults. It also has one key designed to amplify universal connectors when there's not enough volume flowing through them from other devices connected elsewhere along our vehicle's network lines.

1. Connect your scanner to your vehicle

setting up the OBD2 scanner to the DLC port

Find the diagnostic link connector (DLC) in your car. It is a 16-pin connector, slightly similar to a computer VGA, usually under the dashboard just below the steering wheel. Check your car's owner's manual to see where your car's DLC is located. However, it is good to note that not all vehicles with a 16-pin OBD connector are compliant with OBD2 protocols. 

Turn your ignition on, but don't start your engine. Wait for the scanner to establish a connection with your vehicle. You'll see messages like "searching for protocol" and "establishing data transmission link" appear on the scanner's screen.

Check the connection if you don't get any response, as older cars may take some time to connect. Ensure the cigar lighter works, so you're sure you have enough voltage to get the diagnostic link connector working. 

2. Input your car's information on the scanner

OBD2 scanner linking to the vehicle

Select Codes or Trouble Codes on the main menu after booting up your scanner. The information it provides depends mainly on your scanner and the year of your vehicle. Usually, though, you'll have information on different systems on your car, including engine/powertrain, transmission, airbag system, and brakes. 

The scanner will instruct you to choose between Active Codes and Pending Codes. When your vehicle signals to check the engine, it has detected active codes. On the other hand, pending codes are trickier to see since it does not cause the Check Engine light to go. 

When it happens the second time, the vehicle reads it as an Active Code, and the Check Engine indicator turns on. Check your car when the Check Engine light turns on the first time. When it flashes after it lights up, your vehicle has serious issues.

How does an OBD2 scanner diagnose your car?

OBD2 scanners read the On-Board Diagnostics of your vehicle, an onboard computer found inside all modern cars that help monitor car problems such as safety features like airbags and seatbelts.  

They also gauge fuel consumption, emission control systems, road speed, and similar issues by recording live data and recording trouble codes. You connect the scanner using a data link connector to the port of your car, just below the steering column so that it can record all the data regarding your vehicle.  

When the onboard computer detects car problems, it records them as diagnostic trouble codes. If detected for the first time, it records it as a pending code without tripping the Check Engine Light. However, when it happens again, it becomes an active code, triggering the light to illuminate. You can find the Check Engine Light on the dashboard, usually on the tachometer or speedometer of your car. 

It pays to have an OBD2 scanner since it can record real-time issues with your car. Treat all Check Engine Light notifications as urgent, and when you're on the road, it is best to find a safe place to park and have your car towed. 

How to interpret the codes

An illustration of how to interpret the error codes

It is essential to understand what the code means on your OBD2 code readers, even if just the basic codes. Four basic car codes represent your car's systems - the powertrain, body, chassis, and undefined car codes about other issues not covered by the other three.  

Each code will start with a letter that designates what system the code is referring to. Generic codes, also known as the Society of Automotive Engineers (SAE) codes apply to any car while manufacturer-specific codes are specific to a manufacturer like Honda, Ford, etc. Check with your manufacturer or search online to get these codes.

Powertrain (P). The powertrain is the largest set of codes that includes information on the engine, transmission, fuel system, ignition, emissions, etc. These are the codes that trip the Check Engine Light. 

Body (B). This information covers issues related to the body system airbags, seat belts, power settings, etc. 

Chassis (C). This code includes the chassis such as the anti-lock brake system, brake fluid, axles, etc.

Undefined (U). This information covers other aspects of the car, such as module failures and losses of communication.  

For example, if your vehicle has stored a code P0126 and you see the malfunction indicator light (MIL), it means it has a low coolant temperature for stable operation.  

For this particular example, let's break the code down to make it more understandable. Once you've got the code, search here to see what each code entails.  

The first character, usually the letters P, B, C, and U, indicates the issue’s location, whether in the powertrain, body, chassis, or undefined. In our example, the trouble is in the powertrain, thus the code P. 

The second character determines whether the issue is generic, indicated by 0 or manufacturer-specific (numbers 1-3). In our example P0126, we're looking at a generic code, and any car may experience this trouble code, hence code 0. 

An illustration showing the meaning of the third number in your error code

The third character is more extensive since it indicates the particular system affected. For example, code 1 indicates issues in the fuel or air metering system. 

The last two numbers indicate the more specific issue in the subsystem. According to the P0126 code, the issue is low coolant temperature. This error may be due to a low engine coolant level, a faulty thermostat or sensor, or connection problems.  

An illustration showing the symptoms and causes of the error codes on your car

How to erase the error codes after car check

OBD2 scanner showing how to erase error codes

Once your car has undergone the necessary car check and work after your OBD2 scanner reads an error code, you can clear codes without any issues. The check engine light won't go away immediately after you have your car done, but you can reset it by erasing the error code on the OBD2 scanner.  The operation may vary depending on different models, but most scanners have very straightforward instructions on the main menu. 

Is it worth buying an OBD2 scanner?

Before you buy an OBD2 scan tool, know the pros and cons so you can weigh which is best for you. 


1. Real-time updates

Check your car's battery voltage, fuel levels, emissions, coolant temperature, and other vehicle diagnostics data even without opening your car's hood with an OBD2 scan tool. It does the job even when you're driving your vehicle, so you have peace of mind. 

2. Easy installation

You can install a good OBD2 scan tool in less than 5 minutes by plugging in the device, then syncing it with the companion app. 

3. Improves driving behavior

Aside from diagnosing your vehicle's problems, some OBD2 scan tools can store data about vehicle speed, hard accelerations and brakes, and engine idling. You can use this information to improve your driving habits and how they may affect your vehicle's performance. 

4. Save on Professional Fees

There are issues in your vehicle that won't need a mechanic if you know how to diagnose and solve them. Scan your car after you have fixed it to see if you cleared the trouble code. 

5. Prepare your car for state emission tests

If you're getting a state emission test, run the I/M readiness test to see if you can pass the emission test. If you failed the I/M test twice, get your car checked to correct the problem before getting that state emission test. 


1. Drains battery

Don't leave the OBD scan tool because it consumes battery power or turns on your electronic control unit (ECU) and may drain your battery completely, even when your car is not running. Check if your OBD2 scan tool has a sleep mode and how much power it uses in the sleep mode. 

2. Data hack risks

Be sure to see if your OBD2 scan tool has security measures to keep your data secure and ensure that it does not store its data in a public cloud that anyone can access. 

3. Interferes with vehicle electronics

The OBD code reader installed on your car now has access to your vehicle's electronics. However, ensure that your code reader is compatible with the vehicle’s make and model and certified for safety.

Why You Shouldn't Rely on Trouble Codes Alone

Diagnostic trouble codes are not always accurate. Some trouble codes may trip the Check Engine Light of an issue that is not the real problem at all. It is best to consult the owner's manual to back up your diagnostic trouble code. 

If you’re not sure what the code means, you may have to consult a professional to take a better look at your car. The bottom line is, while the OBD2 scanner may diagnose issues with your vehicle, you should not take it as the sole diagnostic tool. 

How to Choose a Good OBD2 Scanner?

• Easy setup

Who wants a complicated diagnostic tool for their vehicles? Choose scanner models that you can set up in less than 10 minutes and come with a smartphone app, making the scanner even better.

• Compatibility

Cars made before 1996 are compatible with OBD1 protocols, but cars made in the US in 1996 and beyond are more compliant with the OBD2 protocols. 

Check the country that manufactured your car to see its compatibility with the OBD2 scan tool. Cars made in the US from 1996 onwards are OBD2-compliant, while Canada had full compliance in 1998. On the other hand, EU cars got full compliance in 2002 for its petrol cars and 2007 for its diesel cars. 

On the same note, cars from other countries have different years of compliance; some have not even achieved full OBD2 compliance. For more US legislation about OBD2 compliance in the US, visit this website. 

• Error code explanations

Not everyone knows how to interpret their scanner's readings, so it is best to get one that offers explanations instead of displaying the error codes alone. 

• I/M Readiness check

Check if your car is I/M ready after installing your OBD2 scanner. The I/M readiness check lets you assess your car's possible performance during an engine and emission test. 

  • It is best to start the test when you haven't used the car in at least 4 hours, so it is completely cooled. Turn it on and let it idle for 10 minutes.
  • Check your oxygen sensor and fuel trim.
  • Hold your vehicle for 1 minute with the brake engaged and in gear to simulate standing at the stoplight.
  • Accelerate to 40MPH at 1/4 throttle, maintain that speed for 2 minutes, and then slow down to 35MPH for another 2 minutes.  
  • Alternate the speed from 25MPH and 45MPH for 5 minutes each, maintaining at 1/4 throttle. 
  • Accelerate to 55MPH for 1-2 minutes before returning to a slower speed and return to your destination. Let the vehicle cool down. You may want to repeat the cycle test to get it in its running condition. 

• Precision

You'll only do well with your OBD 2 scanner if it gives accurate real-time information when you need it. 

• Reads other information

A good OBD2 scanner can read other information regarding your vehicle with just a few taps on your scanner. 

• Graphical data

Some OBD2 scanners can even present your data in graphical form, so it's easier to understand, and you can compare your results. This scanner may cost a bit more, but the extra cost is for convenience.  

• Warranty

Choose a scanner with a lifetime warranty so you can make the most out of it. 

• Additional functions

If your scanner comes with a few extras for a few more bucks, it helps if it has an electrical multimeter, exports PDF files, reads proprietary codes, and has a big, bright screen for easier reading. You can also use it to reset the oil lamp light, reprogram systems, and register your new battery. 

People Also Ask

Will an OBD2 scanner work on a BMW?

Yes, you can use the OBD2 scanner as a diagnostic tool, but first, check the BMW protocols based on the year they were manufactured. Currently, there are three BMW protocols you can check: ISO 9141/2 for cars made in 1996-2001, ISO 9141/2 KWP 2000 for vehicles made in 2002-2006, and ISO 9141/2 KWP 2000 CAN for cars made in 2007-2009 and beyond. 

What scan tools do mechanics use?

After thorough research, it's clear all of these tools have their strengths and weaknesses. The most significant difference between them comes down to functionality which is the primary consideration for professional mechanics who need more service functions, coding ability, and active testing that consistently work with the broadest range of vehicles. 

A professional mechanic needs a reliable diagnostic tool to help him identify the issue easier and respond to its specific needs better. 

How do you tell if OBD codes have been cleared?

When you clear the codes, all emissions tests are reset and display a 'not complete' status. Your vehicle must be driven under different conditions (town driving versus highway) so that it can gather sufficient data from which to determine whether or not the emission has passed.

What OBD2 protocol does my car use?

There are 5 types of ODB2 protocols, and your car, if made later than 1996, must fit one of these. To use your OBD2 scanners as a diagnostic tool to read codes, check your car's OBD protocol type (type A or B) first to narrow your search. Some of the protocols are specific to manufacturers. 

For example, Ford uses SAE J1850 VPW, General Motors use SAE J1850 PWM, while Asian, Chrysler, and European cars use ISO 9140-2 and KWP2000. Some Asian manufacturers use ISO 14230 KWP2000, and lastly, for vehicles made after 2008, they use ISO 15765-4/SAE J2480 (CAN).  

What should I look for in a scan tool?

  • Real-time error detection. It is best to get a scan tool that works in real-time, even while you're driving it. The Check Engine Light should be accurate to signal trouble codes when they arise. 
  • It can be updated. Since manufacturers upgrade their vehicles to make them better every year, it is best to get a scan tool whose diagnostic system you can update online to keep up with these changes.    
  • Retrievable data. Get a diagnostic tool, such as an OBD2 code reader, get a diagnostic tool to retrieve the data stored in the scanner's memory that you can use later.  


We hope this blog post has helped you understand the power of OBD codes. If your vehicle's Check Engine light is on, try using an OBD2 scanner to determine why and if you can fix it without a trip to a mechanic. 

You may also want to consult with a professional to see if you made the correct diagnosis, especially if the issue is more serious. They can even show you how easy it is for anyone to read these five-character codes generated by your car's computer system so you can do it better the next time.