What does it mean when the car's OBD light is on?

[DiAlejandro]

The illumination of the car's OBD light indicates a severe exceedance of vehicle exhaust emissions, serving as the engine exhaust system fault indicator. The primary cause for the OBD light to come on is an emission-related fault in the vehicle. Generally, the OBD light being on rarely prevents the car from starting, meaning the vehicle can still be driven, but it is recommended to seek repairs as soon as possible. OBD, translated into Chinese as the On-Board Diagnostics system, continuously monitors the engine's operating conditions and the working state of the exhaust after-treatment system. It immediately issues a warning upon detecting any condition that might lead to excessive emissions. The engine fault light, on the other hand, is displayed when the vehicle's computer detects a fault in the engine, primarily focusing on operational faults within the engine itself.