This post is for my 4.6 E53. One of my ignition keys will be fine for several months. Then out of the blue will fail. Causing a no crank no start condition. Pull the key out, hum a Rolling Stones jingle, retry.
Starts second time. Until recently. The key just won’t start the X5, consistently.

I have since switched to my back up key. Works perfectly every time.
So I feel I have a wonky key. Since one key works perfectly and the other is
iffy. I don’t exactly know what to do. Both keys have good battery and Fobs work fine.
Now what?

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