Top 3 Things to Check When Buying a Used Car, Using an OBD Device

If you are buying a used car, knowing what things to check for can help you save a lot of money!  

Before purchasing it, you need to know whether you are being sold a used car with severe hidden issues or if you are being part of a scam. Did you know that car scams in the USA defraud people a total of $30 billion per year?

There are many things about the exterior and interior of a used car that you should inspect. However, these are the 3 top things that you should check before anything else. 

  1. Ensure you are not purchasing a stolen car.
  2. Check if the car mileage has been illegally manipulated.
  3. Find out its actual internal health status.

Luckily, you don’t need a car expert or expensive equipment to check for these important things while car shopping.

With your Carly OBD2 scanner and app you can do it extremely quickly and easily from your phone.

After reading this post you will know how to run a used car check and instantly find out if the used car is worth purchasing, or if you can negotiate a better price!

Avoiding car scams with the Carly OBD2 scanner

Bluetooth OBD scanner

The most affordable and convenient solution for having in-depth insights about a used car is to have your own OBD2 scanner. 

However, here you need to be aware that most scanners on the market only offer OBD-level features. This means that they can only show you generic OBD fault codes from the engine, and in some cases transmission ECUs. But not the manufacturer-specific fault codes from all ECUs or even, more advanced features such as a used car check.

But with an OBD2 scanner and app that also offers a “used car check” function, such as Carly, you will be able to get the FULL picture of the internal state of the car plus other hidden information.

With the same Carly scanner, you can conduct as many “used car checks” as you want, and on as many cars that you want. Every check will only take a few minutes and you will instantly know if you are purchasing a good used car or a lemon.

Now let’s dive deeper into how to conduct a used car check from your phone!

Getting ready to perform a used car check

Once you have your Carly OBD2 scanner and app license you are ready to perform in-depth inspections.

Setting up the Carly OBD2 scanner and app is fairly easy and will only take you a couple of minutes! All you have to do is plug the scanner into your car’s OBD2 port, open the Carly app and pair it to your car. Below, we have detailed instructions to guide you through it. 

After setting up your equipment, performing the used car check is quick. As shown below, just go to your dashboard, click over “used car check” and run the test. 

Once you run the used car test, we can start checking out all the information about the car!

3 hidden things to check before buying a used car

From the outside, a used vehicle might look great. Even during the test drive, you might not be able to tell if there are severe internal issues going on.

Therefore, to uncover the REAL information and health state of a used car here are the top 3 things to check before buying a used car.

1. Identify if the car is stolen

If you are considering buying a used car, the first thing that you must check is if you’re purchasing a stolen car. Car theft is more common than you might imagine. 

Even though law enforcement and anti-theft programs have increased their efforts over the years, thieves are constantly devising new ways of stealing and selling cars.

In fact, according to, the number of stolen cars in the U.S increased from 799,644 in 2019 to 873,080 in 2020.

Moreover, if you buy a stolen car, different legal measures may apply to you depending on your country and state. If you unknowingly purchase a stolen car, then you will most likely lose the car and your money. However, if you knowingly buy a stolen car you might even get arrested. 

Therefore, it is crucial that you perform an inspection and uncover if you are purchasing a stolen car or not.

How to check if you are buying a stolen car?

When buying a used car, you can find out if it’s stolen by checking the vehicle’s VIN (vehicle identification number). The VIN consists of a series of 17 numbers and letters that represent its unique identity. There are 4 places where you can look for a car’s VIN:

1. Bottom right corner of the windshield (seen from the outside)

2. Driver’s door framer, in the middle or bottom.
3. Under the hood stamped on the front or top of the engine block (common for gasoline cars)
4. On the front end on the engine frame (common for older cars)

In the case of stolen cars, car dealers may remove it or alter the original VIN number to a fake one. So it’s important to check that the original VIN registered in the car’s control units corresponds with the one stamped on the car.

In the Carly app, after running the used car check, you can see the car’s original VIN by clicking over “Vehicle identification numbers (VIN)”. 

You can then compare the VIN shown on the Carly app to the VIN that is stamped on your car and registered in the car’s sales report. 

If the VIN’s do not match the VIN shown in the Carly app, then someone has altered the car’s VIN.

If the stamped VIN on the vehicle does not match the one shown on the Carly app there are 2 reasons why this could be happening.

Firstly, it can be due to an amateur repair where the part showing the VIN has been replaced for a used one. If this is the case, the worst case that can happen is that the part is not suited for that car.

Or, the reason for not having matching VINs is that the car is stolen and the stamped VINs have been physically altered. If this is the case we advise you not to purchase the car since you might be part of a fraudulent sale.

2. Detect illegal mileage manipulation

Once you have ensured that you’re not buying a stolen car, the next step is to determine if the used car has been illegally manipulated in order to charge you a higher price. 

Odometer fraud is one of the most common ways of pricing used cars higher than their actual value. It is the manipulation of the car’s mileage in order to lower or roll back the number of miles indicated. In the U.S. alone, approximately 450,000 used cars are sold per year with a fake mileage count.

Since mileage is one of the indicators to determine the conditions of a vehicle, low mileage means that the car has not been driven a lot. Therefore, these low-mileage cars have should have a longer lifespan, leading them to be sold for a higher price.

If car scammers manage to reverse a used car’s mileage they can increase the price for up to $5,000. So checking for odometer manipulation on the used car that you are interested in can save you a lot of money!

Luckily, as cars become more technologically advanced, it is possible to detect odometer fraud. There are many ways to detect this, and some methods are more complicated or expensive than others. 

However, the easiest and quickest way to perform an inspection is to run a “used car check” with the Carly OBD2 scanner.

How to detect odometer manipulation on a used car?

If you are checking out a used car and have the Carly OBD2 scanner and app, you can immediately find out if the car’s mileage has been manipulated. Since the mileage of a car is not only stored in the odometer but also in its engine control units, we can learn the car’s real mileage.

To find out the real mileage, click on “Mileages (Carly Check)” after running the used car check. On your screen, you will see similar information to the image below. 

Carly compares the mileages that are stored in the different ECUs. There should be no ECU with more miles than the dashboard’s mileage.

The “current mileage” and the highest mileage on “Span from lowest to highest mileage” should be the same as the mileage displayed on the car’s dashboard.

However, it can happen that the mileage differs by a few kilometers. For example, the current mileage” or “the highest mileage” shown in the Carly app can be slightly lower than the dashboard mileage. This is because the mileage stored in the car’s ECUs is not always synchronized in real-time with the car’s tachometer mileage.

Nevertheless, as a rule of thumb, when the mileage differs slightly, the mileage displayed on the dashboard should always be higher than the mileage stored in the car’s ECUs. 

If the car’s dashboard has lower km’s recorded than the mileage shown in the Carly app, this immediately shows that the car has been manipulated and you should stay away from that car. 

In the case that the car’s odometer has been manipulated, the Carly app will warn you right away. You can see an example in the image below. 

3. Uncover hidden faults and issues

Now that you have checked for fraud and illegal manipulation on a used car, let’s move on to checking a used car’s actual health status. 

When purchasing a used car, many buyers decide on the car based on its looks and the driving experience. And from the outside and interior, and even while test driving, a used car might seem in great condition.

However, any internal problems going on with the car are easy to hide since they are not visible (assuming the engine turns on as expected). 

To purchase a good used car and get a fair deal, we recommend you carry out your own  “inspection” by performing a quick health check with Carly. This way you will find out if there are possible issues present. 

A health check will instantly tell you if there are any faults codes and problems that could cost you thousands of dollars to repair.

Besides seeing what problems the used car has, Carly’s health check also tells you the severity of these issues. Therefore, if you cannot afford to have constant maintenance expenses, this is the quickest way to find out whether to buy a used car or not.

How to check fault codes and the overall health state of a used car

To run the health and diagnostics test, go to “Dashboard” on the Carly app. Then go to “Health” click on “Check for issues”. Your screen will look similar to the image below.

Make sure that the car’s engine is on while the car is being checked. Carly will scan every system in the car for issues. Once the check is complete you will see an overall view of the car’s health.

Depending on the type and severity of the issues found, the health state can range from “Good” to “Bad” and “Very bad”. 

After running the “Health check”, there might be many error codes showing up and so the car’s health might be evaluated as “Bad” or “Very Bad”.  

A tip before moving ahead: After the first health check, we recommend you clear the fault codes and then conduct a second health check. This is because it is possible that the car’s faults have been corrected in the past but were not cleared from the car’s system. So, after clearing old/corrected fault codes it is possible that the car shows that it’s actually in a “Good” health state. 

How to clear fault codes and run a second health check

To clear the car’s fault codes, just click on “Clear issues” as seen in the image below.  

Before conducting the second health check, we recommend you wait 3 days. This is because the car’s ECUs take a while to read out all of the car’s real-time data. As seen above, you can set a reminder in the Carly app after 3 days.

Interpreting a health check

Conducting the second health check should now give you a real overview of the used car’s health state.

If the car’s health is defined as “Good”, that is great news! The used car’s health is in good shape and you can move on to the final step of checking a used car.

However, if after clearing the fault codes the overall health status of the car is “Bad” or “Very Bad” you should pay attention to which faults were detected. Some systems may require more attention than others.  

In the case that the faults are in less crucial systems, such as the rearview camera, you might still purchase the used car since its engine is in good condition. Nevertheless, you can negotiate better prices with the car seller. After all, you still have to repair the systems of the car that these fault codes are related to. 

However, if the fault codes are in more crucial systems then you should reconsider purchasing that specific car. One of the most crucial systems is the engine. Other crucial systems include the transmission, the ABS (Anti-lock Braking System), and the airbags. 

Usually, the repairs and maintenance related to the engine tend to be costly.  Though the price of engine repairs can also vary greatly depending on the car model and year. 

If you are not sure about what the displayed fault codes mean, we got you covered! In the Carly app, after conducting the second health check, you can directly find information about each fault code by clicking on it. As seen below, you will be redirected to Google with the error code automatically copied to find out more about it.

What if you can’t go back to perform a second health check?

If you are unable to go back to the car dealer or seller for a health check 3 days after clearing the issues, don’t worry. 

The first health check should be enough to know if the car had or has a fault code related to a highly crucial system of the car. 

If there are fault codes related to a crucial system, the same logic mentioned above applies. You should reconsider purchasing a car that has severe issues in the critical systems of the car.

Nevertheless, with a second car check, you can definitely know if the fault codes shown in the Carly app are current, or are older issues that hadn’t been cleared out. So, ideally, we recommend you perform the second check.

Health and diagnostics checklist: Questions to answer

Performing an inspection about the car’s internal state will help you learn several important things:

  1. Is the used car in good condition?
  2. If there are fault codes, are they related to crucial systems?
  3. Will you have to deal with repair and maintenance costs after purchasing the car?

Overall, we recommend you to stay away from used cars that have severe fault codes related to the engine and other critical systems. Unless you are willing to spend money on further repairs, you should not purchase a used car with problems that are costly.

Setting up your Carly OBD2 scanner and app

If you follow the checklist above while car hunting, you will be able to uncover hidden issues about your potential new car. Running a “used car check” will quickly help you determine if you are purchasing a used car in good condition. Or even help you renegotiate the price! 

The Carly OBD2 scanner can be used with any car brand in the world that has an OBD2 port. Usually, most cars manufactured after 1996 (in the USA) have an OBD2 port installed. 

However, since every car’s electronics are unique, it depends on your car model which Carly features you can access. Here you can check what features are available for your car!

Once you have your Carly OBD2 scanner and app license you are almost ready to perform in-depth inspections. You just have to set up the Carly equipment. And luckily this is very easy! 

STEP 1) Firstly, open the Carly app on your phone. 

STEP 2) Next, plug the Carly scanner into the car’s OBD2 port and turn on the engine. The car’s OBD2 port can usually be found under the steering wheel on the left side. 

In the table below, you can find the location of the OBD port for your car model. Otherwise, you can also ask the car seller where the OBD port is located or find it in the car’s manual.

STEP 3) Turn on your phone’s Bluetooth and click the orange button that says “connect” in the Carly app. 

As seen in the image below, Carly will establish a connection between your phone and the OBD scanner. Afterward, you will immediately have full access to the car’s information in the Carly app. Now you are ready to check out the car you’re interested in buying!

Keep saving money even after purchasing a used car!

Beyond using the Carly scanner and app to purchase a used car for a fair price, you can keep saving money on its future maintenance needs! By conducting a monthly “health check” with the Carly app, you can save up to $500 on yearly repairs fees.  

The car health checks will tell you if your car needs immediate repair, or if the warning sign that turned up on your dashboard is something that doesn’t require a car technician to fix.

Additionally, you will be able to avoid unexpected costly repairs at the mechanic since you can always know your car’s health. Conducting consistent checks can also help you budget for future repairs. This way you can take action as soon as your car requires it.

Now that you know how to save money during and after purchasing a used car, you are fully equipped to start your car hunt! Are you ready to uncover the real health state of your future car?