What does a check engine light indicate?

The check engine light is an indication that the vehicle's onboard diagnostics system has detected an issue that could affect its performance, emissions, or overall functioning. When this light illuminates, it signals that the vehicle has registered a trouble code that needs to be investigated and diagnosed.

While some issues indicated by the light may not necessarily require immediate action, many can lead to more significant problems if not addressed. For example, a malfunctioning oxygen sensor or catalytic converter might not show immediate severe symptoms, but if neglected, they can impact fuel economy, exhaust emissions, and engine performance. Therefore, treating the check engine light as a signal for potential problems that should be checked out promptly is crucial to maintaining vehicle reliability and performance.

Other options may misrepresent what the check engine light signifies. A minor issue doesn’t accurately reflect the range of problems that could trigger the light. It's also not simply a reminder for routine maintenance, as that would typically involve specific indicators for tasks such as oil changes or filter replacements, not the more diverse issues covered by the check engine light. Lastly, while some aspects of the vehicle’s operation relate to safety, the primary purpose of the check engine light is not explicitly as a safety feature but rather as a diagnostic alert.