Purchasing a used car can be an exciting yet daunting task. While a vehicle might appear flawless externally, hidden mechanical or electrical issues could lead to significant expenses down the road. One of the smartest moves a prospective buyer can make is to utilize a scan tool to check for diagnostic trouble codes (DTCs) before finalizing the purchase. This practice not only empowers the buyer but can also foster transparency with the seller. Let’s delve into why scanning for codes is crucial and what you should be looking for.
Why Bring a Scan Tool When Evaluating a Used Vehicle?
Using a scan tool offers dual benefits, advantageous for both the buyer and the seller in a used car transaction. For buyers, it’s a proactive measure to uncover potential problems lurking beneath the surface. For sellers, especially honest ones, it can instill confidence and potentially expedite the selling process by addressing concerns upfront.
One critical aspect beyond just reading fault codes is understanding when these codes were last cleared. Unscrupulous sellers might attempt to mask underlying issues by disconnecting the battery to reset the check engine light. If a scan reveals recently cleared codes, it should raise a red flag, suggesting potential hidden problems that the seller might be trying to conceal. This is a vital piece of information that a simple visual inspection cannot provide.
Moreover, advanced scan tools can often access data beyond basic fault codes. Some tools can even verify the actual mileage of the vehicle by reading data from different modules within the car’s computer system. This can be invaluable in detecting odometer fraud, where the displayed mileage is tampered with to increase the car’s perceived value.
In a real-world scenario, imagine using a scan tool and discovering a multitude of fault codes in a car that otherwise looks appealing and has a clean dashboard with no warning lights. This exact situation occurred when a neighbor asked for assistance in evaluating a used car. Despite its seemingly good condition and low mileage, scanning all the car’s modules revealed a staggering 72 fault codes. Such a discovery is a clear indication to proceed with extreme caution or, as in this case, to simply walk away and continue the search.
Decoding the Scan: What Codes Are Important?
When you plug in a scan tool, what exactly should you be looking for? Here’s a breakdown of the key types of codes and information to pay attention to:
-
Diagnostic Trouble Codes (DTCs): These are the primary codes to look for. DTCs are alphanumeric codes that correspond to specific issues within the vehicle’s systems, such as engine, transmission, ABS, airbags, and more. A scan tool will read these codes from the car’s computer. It’s important to note down each code and research what it signifies. Websites and apps dedicated to DTC lookups can provide detailed explanations.
-
Pending Codes: These codes indicate problems that have occurred but haven’t yet triggered the check engine light. Pending codes are early warning signs and should be taken seriously. They suggest that a problem is developing and could become more severe soon.
-
History Codes: Some scan tools can show a history of codes, even those that are not currently active. This can reveal intermittent issues or problems that were previously cleared. While not immediately active, history codes can point to recurring problems that might resurface.
-
Cleared Codes and Time Since Cleared: As mentioned earlier, knowing when the codes were last cleared is crucial. If codes were cleared very recently, especially right before you inspected the car, it’s a major red flag. A legitimate seller should have no reason to clear codes unless issues have been properly addressed and repaired.
-
Module-Specific Codes: Modern vehicles are equipped with numerous electronic control modules. A comprehensive scan should check all available modules (engine, transmission, ABS, SRS, BCM, etc.). Fault codes in different modules can pinpoint issues beyond just the engine, affecting safety systems, comfort features, and more.
-
Freeze Frame Data: When a DTC is set, the car’s computer often stores “freeze frame” data, which is a snapshot of sensor readings and operating conditions at the moment the fault occurred. This data can be invaluable for diagnosing intermittent problems and understanding the context in which a fault code was triggered.
Types of Scan Tools for Used Car Inspections
There are various types of scan tools available, ranging from basic code readers to advanced professional-grade scanners. For a used car inspection, you don’t necessarily need the most expensive and feature-rich tool, but a reliable scanner is essential.
-
Basic OBD-II Code Readers: These are the most affordable and user-friendly options. They can read and clear basic engine and transmission codes. They are a good starting point for a quick check but might lack advanced features like reading codes from all modules or providing freeze frame data.
-
Enhanced OBD-II Scanners: These scanners offer more functionality than basic readers. They can often read codes from more modules beyond just the powertrain, and some provide live data streaming and freeze frame information. Many good quality handheld scanners fall into this category and are suitable for thorough used car inspections.
-
Smartphone-Based OBD-II Adapters: These adapters plug into the OBD-II port and connect to your smartphone via Bluetooth or Wi-Fi. Paired with a suitable app, they can offer similar functionality to enhanced handheld scanners, often at a competitive price point. This is a convenient and increasingly popular option.
-
Professional-Grade Scan Tools: These are high-end tools used by mechanics and dealerships. They offer the most comprehensive diagnostics, advanced functions, and in-depth analysis capabilities. While not essential for a typical used car buyer, understanding their capabilities highlights the depth of information that can be accessed through vehicle scanning.
Best Practices When Scanning a Used Car
To effectively use a scan tool when evaluating a used car, keep these best practices in mind:
- Always ask the seller for permission before connecting a scan tool to their vehicle. Transparency and courtesy are key.
- Perform the scan before the test drive, if possible, or at least before finalizing any negotiation.
- Scan all available modules, not just the engine control module. A comprehensive scan provides a more complete picture of the vehicle’s health.
- Record all DTCs and any other relevant information displayed by the scan tool. Don’t rely on memory.
- Research the meaning of each DTC. Understand what systems are affected and the potential severity of each code.
- Pay close attention to the “time since codes cleared” or similar information. Recent clearing of codes warrants further investigation.
- Consider the age and mileage of the vehicle when evaluating codes. Some wear and tear issues are normal in older, higher-mileage cars, but significant or numerous codes should always be a concern.
- Use the scan tool as one part of a comprehensive pre-purchase inspection. It complements visual inspections, test drives, and mechanic inspections, but it’s not a standalone solution.
Conclusion: Scanning for Peace of Mind
In conclusion, bringing a scan tool when looking at a used car is an indispensable step in the due diligence process. It empowers you with valuable information about the vehicle’s internal health, helps detect potential hidden problems, and provides leverage in negotiations or the wisdom to walk away from a potentially problematic purchase. By understanding what codes to scan for and how to interpret the results, you can make a more informed decision and drive away with greater confidence in your used car purchase. Remember, a few minutes with a scan tool can save you from costly repairs and headaches in the long run.
