Can a vehicle pass a Smog Check with a check engine light on?

A vehicle cannot pass a Smog Check with a check engine light on because the functioning check engine light signifies that there is an underlying issue that may affect the vehicle's emissions. This light indicates that the onboard diagnostics (OBD) system has detected a malfunction within the emissions control system, which is crucial for reducing harmful emissions produced by the vehicle.

When the check engine light is illuminated, it suggests that the vehicle has a diagnostic trouble code (DTC) that potentially concerns the engine’s performance or the emissions control components. In California, the Smog Check program requires that the check engine light be off for a vehicle to be eligible for a pass, as it cannot be guaranteed that the vehicle is meeting the necessary emissions standards.

In contrast, while some minor issues may commonly be overlooked in regular vehicle operation, they still need to be resolved for compliance with emissions regulations. Ultimately, the check engine light’s status is a key indicator that the emissions system may not be functioning correctly, which is why a vehicle with this light on cannot pass the Smog Check.