My first trifecta was actuator gear related. The tell-tale was the pronounced 'clicking' on shut-down. I'm having that again [occasionally] and will have to replace rather than just turn the gear. That said, I'm also having intermittent 4wd light alone or trifectas and am replacing the alternator to fix a bad diode. I'll see what remains after the alt fix and replacing the actuator gear. Next step will be an autologic test, I'm thinking its a wheel sensor at one of the corners, but one thing at a time .....

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2006 X5 3.0 6-spd w/Evo UUC ssk
sport/premium pkgs
born Valentine's Day, 2006.