What is the reason for one rear fog light being on and the other off?
4 Answers
The reason why one rear fog light is on and the other is off is that there is only one rear fog light. Reason for having one rear fog light: The main reason for having only one rear fog light is to distinguish it from the brake light. According to the EU ECE R38 regulation, if two rear fog lights are installed, they must be positioned at least 10cm away from the brake lights. Brake light introduction: Generally installed at the rear of the vehicle, the brake light has a red main body color to enhance the penetration of the light source. This ensures that vehicles behind can easily detect when the front vehicle is braking, even in low visibility conditions, thereby helping to prevent rear-end collisions. In simple vehicle models, power passes through a fuse to the brake switch. When the brake pedal is pressed, the switch connects, sending electricity to the two brake lights and one high-mounted brake light, which then completes the circuit through the negative line connected to the vehicle body. The function of the fog light is to make the vehicle visible to others in foggy or rainy conditions where visibility is significantly affected by the weather. The rear fog light is the fog light located at the rear of the car.
I've encountered the issue of one rear fog light not working several times, mainly due to the bulb itself burning out. The lifespan of left and right lights differs, with the right one possibly failing first due to more frequent use. Last time I checked myself, corrosion or dust on the bulb socket caused poor contact, and cleaning it fixed the issue. It could also be a blown fuse, usually located in the small fuse box corresponding to the rear fog light's number. If there's a wiring problem, like a short or open circuit, rain or vibration can worsen the situation. Troubleshooting is simple: first try replacing the bulb, then check the fuse, and finally inspect the wiring connections. While this issue isn't major, it's annoying and reduces safety at night. Regular maintenance should include checking the light cover's seal to prevent moisture. Proper handling saves time and money, but for complex cases, a professional shop ensures safety and avoids hidden risks.
In my car repair experience, when one rear fog light works while the other doesn't, it's mostly due to bulb failure or circuit issues. A burnt-out bulb is the most common cause and can be fixed by replacement. Loose or oxidized lamp sockets causing unstable contact can be identified by abnormal voltage readings using a multimeter. Check the fuse protecting the circuit too, located in the fuse box under the dashboard. For wiring, short circuits or breaks often occur at connection points around the light assembly. Additionally, worn switch contacts or relay failure can affect signal transmission. I recommend simple self-checks, but without tools, just take it to a repair shop. Don't wait until rainy days to risk safety - prioritize timely repairs. Regular light system inspections prevent aging.
When the rear fog light is half-lit and half-off, it significantly reduces the warning effect, doubling the risk of driving in foggy conditions. Common causes include a burnt-out bulb or moisture and rust on the lamp socket affecting the current. It's not uncommon for cable damage to cause a short circuit, possibly due to animal bites or aging. I've seen a friend carelessly get electrocuted while attempting a DIY repair—way too dangerous. Address the issue as soon as it's discovered; otherwise, you might fail the annual inspection or run into trouble with traffic police. Safety first—don't delay. Replace the bulb or have a technician inspect the wiring system for a thorough fix.
