On my 97 C280, the rear pads have no wear sensor. I believe rear wear sensors are only present on cars equipped with ASR, and my vehicle does not have ASR.

Check the pads visually for wear.

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Ali Al-Chalabi

2001 CLK55
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record