What would cause Audi rear brake light to not work?

Rear brake light working can tell the driver behind you that you’re slowing down or stopping, it’s very crucial for road safety. Once you are told the rear brake light doesn’t work, you should have a check on the car.


How do Audi brake lights work?

There is a switch near the top of the brake pedal, the brake light is triggered by the switch when hitting the pedal. On the newer vehicles built within the last decade or so, a simple wiring circuit is connected to the car’s body control module (BCM) and rear brake lamps. When the switch is closed, will trigger the BCM to turn on the power for brake lights. This system is powered and protected by a fuse located inside the fuse panel under the dash or the power distribution center located under the hood.


Around this system, we can find the causes for brake lights not working.

What may cause brake lights not working?

Burned out brake light bulb is the cause in most cases, blown fuse, switch damaged, poor connection at the bulb socket, loose or frayed wiring, electrical circuit problem in BCM also can make the brake lamps stop working. Compared other causes is simple and easy to fix, the electrical circuit problem in BCM is more difficult, and we will have a detail description on this with Audi A4. After the exclusion of other possible causes to make brake light not working, we come to BCM, first disassemble BCM from car, and open the case, there is a driver IC chip that controls the power to brake light on electronic board, tested and found the IC chip doesn’t work, replace a new one, no coding is required, then assemble BCM back to its original position, go back to car and press the brake pedal, the brake light start to work again.


Important note: Never disconnect or connect a BCM body control module with the battery cables connected. You can damage other electronic components connected with BCM and you can even blow out other parts. After you find the BCM location, ensure you can safely unplug and plug the connector. Figure out the unplug connector order: first unplug weak electricity socket, then strong electricity socket. When install back the BCM, also follow the plug connector order: first plug weak electricity socket, then strong electricity socket. Generally thick wire is strong electricity, thin wire is weak electricity. Big socket pin is strong, small socket pin is weak. Once the order is wrong, it may happens the cigarette lighter doesn’t work after brake light start to work, the solution is correct unplug and plug the BCM again.


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