What is the reason when the high beam doesn't work but the low beam is normal?
2 Answers
Reasons for high beam failure: 1. When turning on the headlight switch, neither high nor low beams work: Check if any fuse in the fuse box is blown, and whether there's a fault between the car light switch and the dimmer switch. 2. The live wire of the dimmer switch is connected to both high and low beam terminals: If all lights work, it indicates a fault in the dimmer switch. If only the high beam works when connected while the low beam doesn't, the fault lies between the dimmer switch and the headlight or between the dimmer switch and the low beam. 3. The high beam doesn't work: Check if the high beam indicator light is on. If it is, the fault is between the terminal board and the headlight. If not, the fault is between the terminal board and the dimmer switch. Related information: If the bulb burns out immediately when turning on the light switch, check for any short circuit in the charging circuit. If bulbs frequently burn out, check whether the voltage of the generator voltage regulator is set too high.
I just encountered this issue while driving—the high beams suddenly went out, but the low beams remained on. The most likely cause is that the high beam bulb has burned out. Many cars use H4 dual-filament bulbs, where the high and low beams have two independent filaments. If one burns out, the other continues to work normally, which is common. Next, check the fuse—some models have a separate fuse for the high beams. The fuse box is usually located under the steering wheel or near the engine hood; see if any fuses are blown. If the fuse is fine, the issue might be with the switch, such as poor contact in the control stalk on the steering wheel. I had this problem last time—the stalk got stuck due to long-term wear and aging. If you're handy, you can replace the bulb or fuse yourself, but I recommend getting a thorough inspection at a repair shop to avoid accidents from poor visibility while driving on the highway at night. Regular bulb replacements can prevent this—don’t wait until the problem becomes serious.
