jack up the car and remove the plastic liner underneath it, On later W210 it had trap doors in it to service the fog lamps themselves, That sensor was reachable if you had child sized hands.

removing the bottom splash panel is easier.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)