I had this very same problem. Replace your bulbs with Sylvania brand bulbs. Apparently they are the OEM. BMWs measure the impedance of the circuits and report discrepancies as failures. I had some Philips brand bulbs in my tail assemblies and replaced them with Sylvania's. It solved the problems!
BMWs measure the impedance of the circuits and report discrepancies as failures.
This is correct, it measures resistance to current. If it rises above a certain specification, it will read as a dead bulb, even though the lights work. Sometimes just cleaning the socket contacts or bending them out slightly resolves the problem.
If it says brake circuit failure, and your brakes work fine and you think that none of the lights are out, then check the wiring harness in the trunk. It's easy, just open your trunk lid and on the left nahd side look where the wires come from the car and up into the trunk lid. Check that they are in good shape and line up well.
I had a brake light circuit fauilure OBC message all the time, but my brake lights worked fine, turns out some of the wires had been bent back and forth enough times that they broke. This can cause all sorts of electrical havoc too. It's worth a look, there are plenty of DIY to fix this problem too.
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