Went over to visit a friend yesterday. He has a long, steep, narrow driveway.
I pulled in nose first and went inside to help on a fireplace project.
After a few hours it had cooled down outside. I started the engine and thought
I pushed the button for the seat heater. I started backing down the long driveway.
The front end was popping, the brakes were chattering, the brake pedal was pulsating.
WTF???? all I need is a sick BMW New Year's Eve.

I backed down the driveway till the roadway. I then put the X5 into Drive.
I looked down and noticed that I had actually depressed the hill decent button.
Upon finding my mistake, I clicked off that button.

I'm assuming the hill decent button doesn't work correctly when backing down
a hill.
Easy mistake to hit the wrong (yet very close) button then wonder what's going on.

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2003 4.6is X5
2003 525it
2003 E53 X5 Standard shift