Ignoring a solid or flashing Check Engine light can lead to costly repairs, safety issues, or a breakdown. At O’Reilly Auto Parts, our parts professionals can scan and read your Check Engine light for free using O’Reilly VeriScan®.

VeriScan® provides a detailed report of possible causes and fixes, printed for review in-store and sent digitally to your email. This helps you understand what parts or services are needed to restore your vehicle’s performance.

Our team can help you find the right parts and offer guidance for repairs, or recommend a local repair shop if you prefer professional service. For more on what your dashboard lights mean, check out our guide on dashboard warning lights and common Check Engine codes.

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If the Check Engine light comes on in your vehicle and you can safely drive to your local O’Reilly Auto Parts location, we can help you better understand the problem with O’Reilly VeriScan®. Vehicles 1996 or newer can be scanned by plugging our O’Reilly VeriScan® code reader into your OBD-II system – just ask for a free Check Engine light test. The parts professional will follow you to your vehicle with an OBD-II code reader, hook up the scanner to your vehicle’s OBD-II port, and provide you with the diagnostic trouble codes (DTCs).

The diagnostic code or codes are run through a comprehensive database of over 650 million verified fixes in our store, and the fixes and diagnostic information will be explained in your printed O'Reilly VeriScan® report. After your O’Reilly VeriScan® report is complete, you will be able to review your report to find ASE technician-verified solutions, repair options, and suggested parts.

Our parts professionals can also help you find the parts and tools you need to complete your repair. If you are not confident performing the repair yourself, or if additional diagnosis is necessary, we would be happy to refer you to a trusted local repair shop.

The O’Reilly VeriScan® report reflects information provided by the vehicle’s computer and does not replace a full mechanical inspection. O’Reilly VeriScan® is a free service available during store operating hours. No appointment is necessary, though wait times may vary.

Repair shops often charge around $100—or about an hour of labor—to read Check Engine codes. You can save money by getting a free O’Reilly VeriScan® test at O’Reilly Auto Parts and handling repairs yourself.

At O'Reilly Auto Parts, we offer FREE code reading services using our O'Reilly VeriScan® tool, which can read your vehicle's codes and help you understand the problem. This service is available for more than just your Check Engine light, and can also provide details about maintenance lights, ABS warning lights, and transmission codes.

A Check Engine light can illuminate for a variety of reasons, ranging from minor issues to serious problems that may affect drivability or vehicle safety. Understanding the potential causes and which vehicle systems are involved can help you take the right next steps.

Vehicle Systems That May Trigger the Light

Modern vehicles monitor several critical systems that can cause a Check Engine light to turn on:

Emissions system components and oxygen (O2) sensors
Fuel delivery and fuel management systems
Ignition-related components
Air intake and airflow sensors
Evaporative emissions (EVAP) system monitoring

These systems continuously report data to your vehicle’s onboard computer, and a sensor reading outside its normal range can trigger the warning light.

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Common Causes

Even if your vehicle appears to drive normally, the Check Engine Light may activate due to:

Engine misfires: Bad spark plugs, spark plug wires, or ignition coils; or a too-rich/too-lean air-fuel mixture. Misfires often cause a flashing Check Engine Light, signaling an urgent issue that can damage the engine or catalytic converter.
Failing engine sensors or electronic modules: Components like the mass air flow (MAF) sensor or engine knock sensor may produce inaccurate readings, triggering the light.
Emissions problems: Oxygen sensors, exhaust gas recirculation (EGR) issues, or a clogged catalytic converter can all cause illumination
Other triggers: Loose gas caps, disconnected sensors, or minor electrical faults can also cause the light to come on.

The way your Check Engine Light behaves provides important context about urgency:

Solid light: Usually indicates a non-urgent condition. Short trips may still be possible, but a code reader scan should be completed soon, and any necessary repairs should be made.
Flashing light: Signals a serious problem—often an engine misfire—that can damage the engine or catalytic converter. Minimize driving and get a scan immediately. Continued driving with a flashing light can result in permanent engine damage.

By noting whether the light is solid or flashing and understanding which system triggered the alert, you can make informed decisions about diagnostics, repairs, or monitoring.

An O'Reilly employee holding an OBD scanner to diagnose a Check Engine light.

ABS, Transmission, and Maintenance Light Scanning with O’Reilly VeriScan

In addition to free Check Engine Light testing, O’Reilly VeriScan® can scan ABS, transmission, and maintenance warning lights on many vehicles. A free scan helps you understand what your vehicle is reporting and what steps to take next.

ABS Warning Light
An ABS light may signal low brake fluid, a faulty wheel speed sensor, or ABS module issues. O’Reilly VeriScan® reads ABS codes so you can identify likely causes and decide whether repairs or further diagnostics are needed.
Maintenance Lights
Maintenance lights indicate upcoming service needs, like oil changes, fluid checks, or tire rotations. O’Reilly VeriScan® can read or clear these lights and provide mileage-based recommendations, helping you stay on top of routine maintenance.
Transmission Warning Lights
Transmission lights or driveability issues can indicate problems that need prompt attention. VeriScan® retrieves transmission codes so you can understand potential causes and plan next steps, whether DIY or professional service.

Stop by O’Reilly Auto Parts for a free O’Reilly VeriScan® to check your Check Engine, ABS, transmission, or maintenance lights and take the next step with confidence.

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When you have your Check Engine light tested at O’Reilly Auto Parts, our Professional Parts People can read your codes and provide an O’Reilly VeriScan® report with a list of possible solutions, but legally they are not allowed to clear the DTCs causing the Check Engine light with the code reader.

Except where prohibited by law, customers are welcome to use our code readers to clear the codes themselves, which may temporarily turn off the Check Engine light. If the problem is more extensive than a sensor that needs to be reset and the issue has not been addressed, the Check Engine light is likely to reactivate. Even if the Check Engine light is off for some time, it may turn back on as soon as the issue returns or the next time the car is started.

An O'Reilly employee holding a VeriScan report and presenting it to a customer.

Understanding Diagnostic Trouble Codes (DTCs)

Since 1996, vehicles have used OBD-II protocols to let their computers self-diagnose engine and sensor issues via Diagnostic Trouble Codes (DTCs). Sensors and modules send these codes to the engine control module (ECM), where they’re stored and can be read with a diagnostic scan tool or code reader through a connector usually located under or near the dash. Reading these codes helps identify needed repairs and turn off the Check Engine light.

Vehicles made before 1996 may still have a diagnostic port using older OBD-I protocols, which require different tools or procedures and cannot be scanned with the O’Reilly VeriScan® tool.

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Why did my Check Engine light come on after an oil change?

This can happen if a gas cap was loosened, a sensor was disconnected, or a system was disturbed during service. In some cases, the Check Engine light may instead serve as a maintenance reminder depending on the vehicle. A free O’Reilly VeriScan® scan can help determine the cause.

Can I reset my Check Engine Light myself?

Yes, an OBD-II scanner can clear codes. However, if the underlying issue isn’t resolved, the light will likely reactivate. Reviewing your VeriScan® report first helps identify what triggered the light.

Can I Use O’Reilly VeriScan on my own OBD-II code reader?

Yes, the tools we use to scan your vehicle are also available in-store, and can be purchased if you would prefer to perform your own scans at home. These tools are loaded with the same technology that powers O’Reilly VeriScan®, and will provide the same feedback you would receive with an in-store test. The reports generated can also link you directly to OReillyAuto.com to shop for the parts you need to make your repair.

A Check Engine light doesn’t have to create uncertainty. A free Check Engine light scan at O’Reilly Auto Parts helps identify DTC codes, understand which vehicle systems are involved, and determine practical next steps using a clear O’Reilly VeriScan® report.

Drivers choose O’Reilly VeriScan® for our knowledgeable team members, easy-to-understand scan results, and support for most 1996 or newer OBD-II–equipped vehicles. O’Reilly Auto Parts also provides several other free store services including alternator and starter testing, wiper blade installation, headlight bulb installation, and fluid and battery recycling. Stop by any O’Reilly Auto Parts location today—no appointment necessary.

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How Does Free Check Engine Light Testing with O'Reilly VeriScan Work?