Reset the dashboard warning lights on a x5 e53 bmw 2006

On a 2001, and because it is only on one side of the vehicle, and because it is the drivers side only, my guess is that the wire that goes from the driver's door to the door frame is damaged. The best course of action would be to take it to an auto electrician for diagnosis with their pro grade scan tool computer. There are some other theories in the link.

https://www.google.com/search?q=2001+BMW+X5+e53+left+side+front+and+rear+doors+will+not+unlock

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Fuse box is located behind glove box and check fuses No. 26, 32 and 33

https://www.youtube.com/watch?v=rQn5J47ElwU

Check online BMW Workshop Manuals for X Series E53 X5 3.0d (M57) in the attachment: http://workshop-manuals.com/bmw/x_series_e53/x5_3.0d_m57_offrd/2_repair_instructions/12__engine_electrical_system_(m57)/21__preheating_relay/1_ra__removing_and_installing_replacing_relay_for_glow_plugs_(m57)/

Glow plug relay is under inlet manifold to the rear of the engine

Probably an accessory fuse in the dash fuse panel or under the bonnet?

it has been known to be the brake light switch

A combination of items, transfer case chain, electronic actuator or VTG control unit, have you scanned it yet

Diffen Gunari

for better result download the pdf file
1999 2006 Bmw X5 E53 Workshop Service Repair Manual

It means one of your side lights is blown. The lighting computer does a periodic check of all the lights and flags it on the the dash if one is bad. Turn on the lights and walk around the vehicle. Also check the blinker lights.