[tulumsea]

Does an X3 engage the Xdrive AWD in reverse if wheels are slipping? Slippery ice and snow on a slick downhill driveway...

[Wgosma]

By definition, a modern AWD vehicle has both axles/all 4 wheels ALWAYS 'engaged'./powered thru the drivelines.

The BMW X-Drive system can operate in Normal mode or Traction mode (advisable on snow, etc). You can set the mode via cockpit control button.

Normal Mode: power is split, 50% to both the front and rear axles.

Traction Mode: 60% to rear wheels, 40% to front wheels.

This above info in Owners Manual.

[KC87ZB]

The answer is yes, xDrive works forward and reverse.

However, your concern about a slick downhill driveway is more of a stopping concern than a going concern. xDrive will not stop you any better from sliding downhill; it only helps provide accelerating traction.

[andreigbs]

On steep inclines that are icy/snowy, you would benefit from snow tires.

That and very slow speeds are your friend.