chikoo

Reference: https://mbworld.org/forums/5714151-post17.html

So here is the story. I purchased my 2010 ML350 in Jan 2013 with 26K miles on it. I had it checked out by the local eurosport car shop @ DFW and they OKd it with brake wear @50% remaining in front and about 40% remaining in Rear.

Six months later I get the "BRAKE WEAR" sensor show up at 35K miles.

So I take it to the Mercedes Benz of Plano dealership to have it checked out as I had suspected malfunctioning sensor. I tell my service adviser that visually I can see the brake pads are decent enough from the outside. I leave the car with them and they call me back in the noon with this report "my outer pads look fine but inside are worn out", which is why the sensors have been activated.
I take their word for it and since I wanted to go Ceramic, I ordered Akebono ProAct brake pads. (https://mbworld.org/forums/5715453-post22.html)

Today, I get to my neighborhood carcare center (Parkway Carcare) and ask them to replace the brake pads. They do what I told them to do, and they also returned the old pads. The fronts are indeed 50% left, and the rear about 35% left, worn equally inside and outside.

Questions:
1. Why did the Brake Wear Sensor came on?
2. Why did the MB Dealer LIE to me?

Here are the pictures of the Front Brake Pads for your reference


Here are the rear pads

mb techman

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chikoo

I wish I could show a picture of the wear sensor. I did not get those back. Darn it.

From what I understand, the flat surface of the wear sensor has to wear off in order for it to close the circuit for the warning to come on. Correct me if I am wrong. So how does a lip make any difference?

Moviela

The circuit is always closed when the sensor is good. If the pad wears to the point the sensor loop is exposed to the rotor the wire is broken (open circuit) and this turns on the brake warning.

Looking at the remains of your sensor in the picture, MB Techman called it correctly. The wires were cut off by the lip on the rotor. Proper dressing of the wires can prevent that. I hope you measured the rotor for thickness and runout and replaced it if necessary. Workshop refinishing is not allowed. They are so cheap, you might as well have the increased safety of new.

mb techman

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chikoo

Got it. Thanks MBTechman and moviela.

I thought it would be a open -> closed circuit because the "Brake Wear" warning was only triggered when I pressed fully on the brakes. There were days when no warning came up when the temp fell from the 90F to 70F too.

hertaw

I think you can give break sensor picture then i would give you better answer,
But!I understand, the flat surface of the wear sensor has to wear off in order for it to close the circuit for the warning to come on.
Give me suggestion if i am wrong! Thanks