If the trailer lights are LED, that's most likely what's causing the issue. Sometimes mine indicates my left trailer bulb needs to be checked the first time I start my X5 with the trailer connected. The notification clears and the brake lights always work.
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2013 Jerez Black E92 M3 DCT ZCP | PFC Z54/Z45 BBK | MCS 2-way Remote Dampers | Hypercoil 600/900lb Springs | Ground Control Race Camber Plates | Bimmerworld Control Arm Bearings | Powerflex Sway Bar Bushings and Shock Mounts | EDC Delete | Macht Schnell Stage 2 Intake | Akrapovic Exhaust | Bimmerworld Race Studs | CSF Radiator | CSF Oil Cooler | Bimmerworld Power Steering Reservoir | Euro MDM | Lux H8 160 | BMW CF Front Splitters | BMW CF Competition Rear Spoiler | Schroth Quick Fit Pro | HRE R43
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