What is the reason for one side of the rear fog light being on and the other side off?
2 Answers
It is normal for one side of the rear fog light to be on and the other side off, as vehicles are equipped with only one rear fog light. The side that does not light up lacks the lighting configuration. Design principle of rear fog lights: Referring to the vehicle manual, it can be seen that only one rear fog light is functional, while the other is designed symmetrically for aesthetic purposes. According to European Union regulations, if two rear fog lights are installed, they must be positioned more than 10 cm away from the brake lights to avoid confusion with the width indicator lights and brake lights. Therefore, national regulations stipulate that only one rear fog light should be designed, located on the left side of the vehicle, to make it more noticeable. Function of rear fog lights: The light from the rear fog light can penetrate fog in heavy fog conditions, thereby alerting vehicles behind. Hence, the light is more intense, glaring, and penetrating, enhancing driving safety.
When one side of the rear fog light is on and the other is off, I've encountered this issue several times. It's usually caused by a burnt-out bulb or poor contact. A single-sided bulb burnout is the most common reason, as fog light bulbs have a limited lifespan, and prolonged use may cause the filament to break. Next is poor contact due to a loose or corroded plug, especially in older cars where the plug can easily come loose after bumps. You can check it yourself: first, identify which light isn't working, unscrew the lamp cover, and try replacing it with a new bulb—usually, a cheap one costing a few dozen yuan will do. If it still doesn't light up after replacement, check if the fuse is blown; the fuse box is located under the steering wheel or in the engine compartment, as indicated in the manual. Short circuits in the wiring are less common, but be careful not to let moisture corrode the connections. Fog lights are crucial; without them in foggy conditions, the car behind you can't see your position clearly, posing a significant safety hazard. I recommend not delaying and fixing it as soon as possible or taking it to a shop for inspection.
