I just went through the wiring schematic for the headlamps. Nothing makes sense as to why one would work and not the other. The switch sends one signal (one wire) to distribute the power. Both sides and both beams have a common ground, so if one side stopped, it would be both high and low beam. The switch sends one signal to the body control module, when then powers the low beam / high beam relays. In turn, the relay distributes power to the bulbs.
Now the relays are not typical relays. They are PCB relays. Basically, that means they are part of a printed circuit board and are not serviceable. I attached several pics below of the system. The first one is the PCB relay. Next, I attached the entire system. Take a look through it to see what I am referring to. In all honesty, the first thing I would be checking in this situation would be the sockets themselves to see if they are damaged, overheated, corroded, or anything that could cause such an issue. Also, if the light isn't working, take a test light or volt meter and confirm there is no power to the socket.
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https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester
https://www.2carpros.com/articles/how-to-use-a-voltmeter
https://www.2carpros.com/articles/how-to-check-wiring
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Let me know what you find. I hope something here helps. Now, if both low beam stopped, that could be a totally different situation, so let me know.
Take care,
Joe
Images (Click to enlarge)
Jan 25, 2020 at 8:22 PM
