+1 on the multi-meter.

I was NOT endorsing the use of a light bulb for any BMW related testing. It was a JOKE. Like looking for gas flow with a candle or testing for secondary voltage (coil) with your finger.
I worked for a company many years ago that built and sold that large now obsoleted BMW Engine Diagnostic tester sitting in the corner at your local BMW dealer. So I understand all to well the advances in auto diagnotics and proper test proceedures. I follow the old adage, "Test and Measure - Don't Guess"...

You know for sure the discs should be replaced if they start to look like this:
http://www.curlyk.co.uk/S2Forum/WholeDisc.jpg

You can get away with only replacing the discs every other set of pads, but in doing so, you are reducing your potential braking performance to that of a 1960 Chevy Impala. Yes, the brakes work, but I would start doubling the distance to the car in front of you...

Good Luck and welcome to the family of X5 owners. Keep us posted on your progress and efforts.

Oh and +1 on turning off the BOLD posts.

:wow:
Love that metal to metal look. Friction material pull off the pad? I assume it was a race car based on the two piece drilled rotors.

Not mine, found it via google. From the looks of it, they had a sticking caliper on the outside (Audi forum, so fixed 4+ piston calipers), which wore that one side very quickly. And if the pad sensor is on the inboard pad, it would have never registered a wear light, but how did this person not noticing the HORRID grinding sound when the pads wore down to the backing plate?

My rear discs are pretty low. Seems like they were never changed..because compared to the front, they are extremely low.

Turned up the radio? :rofl:

I hear that tell tale noise all to frequently....
My best story on "I trashed my car but did not notice", was the customer who brought in a flat tire in the trunk with nothing left but the center section with the bolt holes left. The rest had been burned off one MM at a time, including 20% of the ball joint and lower control arm on the right front. Oh and 40% of the rotor. :wow:

etched/stamped on the rotor hat is the minimum thickness. use a caliper to measure the disc thickness at the thinnest area. generally, if there is a raised lip at the very edge of the disc, you need to replace them. My experience has shown that the front discs need to be replaced everytime with the front pads. The rear discs generally can get two sets of pads before needing to be replaced. But, that is all dependent on driving style.
Don't turn your discs as you lose even more disc material and will definitely be under the minimum thickness at that point. This also puts you at having higher chance of getting warped rotors. Cheap new rotors also have a very high risk of warping (if not a guarantee of it).
I'll bet that none of your previous vehicles could stop as fast or with as much control as a BMW either. Think of your chassis/suspension as a whole. To be at the highest level of safety (or grip/traction) you suspension, brakes, and tires all need to be in good condition. Your DSC system relies on all 3 parts to work effectively; or if driving with DSC off, You need all 3 parts for maximum control. All 3 are only as good as the worst component. If you don't care, might as well be driving a Hummer or Escalade...ok, rant over.