Why is the led brake light on but not on when driving

This needs to check the circuit of the running lights. Generally, it is either a circuit failure or a damaged bulb. If the circuit is powered after the inspection, then the bulb is broken and needs to be replaced. If the car inspection finds that the line is out of power, it means that the line is faulty and needs to be repaired.

The brake lights of the car are at the rear of the car, while the daytime running lights are at the front of the car. The brake light is a relatively penetrating red light, which is more convenient for vehicles coming from behind to detect that the vehicle is decelerating or stopping even in low-visibility road conditions, which can effectively avoid rear-end collisions. The daytime running lights are designed to allow the vehicle to be easily recognized when driving during the day. They are not designed for the driver's driving line of sight, but mainly exist as signal lights. Cars equipped with daytime running lights will be more visually cool, and can reduce the incidence of traffic accidents, so that pedestrians and visitors can identify the car and avoid collisions. Therefore, both brake lights and daytime running lights can improve driving safety.