Buying a used car can be a smart financial decision, but it also comes with potential risks. One common tactic some dishonest sellers use is to clear the OBDII (On-Board Diagnostics II) codes just before showing the vehicle to potential buyers. This temporarily turns off the check engine light, masking underlying mechanical issues. As an expert in auto repair at autelfrance.com, I’ll guide you through how to detect if OBDII codes have been cleared, ensuring you don’t fall victim to this scam.
The OBDII Code Clearing Scam Explained
The check engine light is your car’s way of communicating potential problems. When your vehicle’s computer detects an issue, it triggers a diagnostic trouble code (DTC) and illuminates the check engine light. Dishonest sellers know that a lit check engine light is a major red flag for buyers. To bypass this, they might disconnect the car battery or use an OBDII code reader to manually clear these codes.
Why would a seller do this? Simply put, to hide existing problems. Clearing the codes is a temporary fix that doesn’t address the actual mechanical issues. The check engine light will likely reappear after some driving, but the seller hopes to make the sale before that happens. This deceptive practice can leave you with a car requiring costly repairs shortly after purchase.
How to Detect Cleared OBDII Codes
Fortunately, there’s a straightforward way to check if OBDII codes have been recently cleared: by using an inexpensive OBDII code reader and checking the “I/M Readiness” monitors.
What are I/M Readiness Monitors?
I/M Readiness monitors are diagnostic tests that your car’s computer runs to ensure all emission control systems are functioning correctly. These monitors check systems like the oxygen sensors, catalytic converter, evaporative emissions system, and more. When OBDII codes are cleared, these monitors reset to a “not ready” or “incomplete” status because the tests haven’t had enough time to run since the reset.
Using a Code Reader to Check I/M Readiness:
Here’s how to use a code reader to check the readiness monitors:
- Plug in your OBDII code reader: Locate the OBDII port, usually found under the dashboard on the driver’s side. Plug in your code reader with the car turned off.
- Turn the ignition to “ON” (engine off): Turn the key to the “ON” position without starting the engine. This powers up the car’s computer and the OBDII system.
- Navigate to “I/M Readiness”: On your code reader, navigate to the “I/M Readiness” or “Readiness Monitors” section. The exact menu name may vary depending on your code reader model, but it’s usually easy to find.
- Check the monitor status: The code reader will display the status of each monitor. You’re looking for “ready” or “complete” versus “not ready” or “incomplete”.
Interpreting the Results:
- All or Most Monitors “Ready”: This is a good sign. It indicates that the car’s systems have been tested and are functioning, and the codes were likely not recently cleared.
- Several Monitors “Not Ready”: This is a strong indication that the OBDII codes have been recently cleared. It takes time and driving cycles for all the monitors to reset to “ready” after codes are cleared. If multiple monitors show “not ready,” especially for systems that should run quickly (like oxygen sensors), be very suspicious.
Emission Standards and “Not Ready” Monitors:
Keep in mind that emission testing standards allow for a certain number of “not ready” monitors, especially for older vehicles.
- Model years 1996-2000: Can typically pass emissions with up to two monitors “not ready”.
- Model years 2001 and newer: Can typically pass emissions with up to one monitor “not ready”.
However, when buying a used car, seeing any “not ready” monitors should prompt further investigation, especially if the seller claims there are no recent repairs or issues. It’s always best to ask the seller why the monitors are not ready and consider a pre-purchase inspection by a trusted mechanic.
Beyond Cleared Codes: Other Used Car Scams
While detecting cleared OBDII codes is crucial, be aware of other scams when buying used cars privately:
- Jumped Titles: The seller isn’t the legal owner listed on the title. This can lead to significant legal and registration problems. Always verify the title matches the seller’s ID.
- Liens Against the Title: The car has outstanding debts or loans attached to it. Check for liens before purchasing to avoid inheriting someone else’s debt. Services are available online (like in Arizona) to check for liens using the Vehicle Identification Number (VIN).
- Hiding Engine Problems: Sellers might avoid letting you start the car from cold at their home to conceal issues like leaks or head gasket problems that are more evident when the engine is cold. Insist on a cold start and check for leaks.
Conclusion
Detecting cleared OBDII codes is a vital step in protecting yourself from used car scams. By using a simple code reader and checking the I/M Readiness monitors, you can gain valuable insight into the vehicle’s history and the seller’s honesty. Remember to be vigilant, ask questions, and consider a pre-purchase inspection to ensure you’re making a sound investment. Don’t hesitate to walk away if something feels suspicious – your peace of mind and financial well-being are worth more than any deal that seems too good to be true.
