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E63AMG, SLK32AMG, Ferrari 348 Spyder, R350 Bluetec, Eagle Talon TSI/AWD, Jeep CJ7, Smart EV
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300 Posts
Discussion Starter #1
Once I have my pads, rotors and brake wear sensors replaced (both front and rear), will the indicator on my dash go off automatically or must I have it reset?

J
 

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E63AMG, SLK32AMG, Ferrari 348 Spyder, R350 Bluetec, Eagle Talon TSI/AWD, Jeep CJ7, Smart EV
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300 Posts
Discussion Starter #3
How long until the error disappears? I've had the work performed, new sensors installed and the wear indicator still shows 'brake wear' on my dash. The sensors are correct and everything was triple checked.

J
 

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2005 C240 silver, 2008 R320CDI Cubanite
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I just changed my rears after the wear sensor warning came on. It went off automatically after installing the new pads and sensors. Quadruple check your install!

Just a note. there is only one side that has the wear sensor. And not all aftermarket pad sets have a new wear sensor. Is there a chance than the mechanic re-installed the old wear sensor?
It is very simple, just 2 copper wires that get cut when they come into contact with the disk. Perhaps the old ones where not connected properly or the wire got cut.
 

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E63AMG, SLK32AMG, Ferrari 348 Spyder, R350 Bluetec, Eagle Talon TSI/AWD, Jeep CJ7, Smart EV
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Discussion Starter #5
I have new wear sensors front and back. The mechanic did not reuse the old ones. Is it possible that the new sensors are the wrong impedance or otherwise not proper for the Benz? My new sensors are aftermarket and not OEM.

J
 

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2005 C240 silver, 2008 R320CDI Cubanite
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390 Posts
You have a few high end cars in your stable. I am sure you are not a newbie in dealing with your repair shop. I suggest you ask your mechanic to trouble shoot this at his expense. As I mentioned, the wear sensor is a simple open/short device. An easy trouble shoot by checking them or shorting them out. If your mechanic can't figure that out maybe you should change mechanic!

I included a photo of a new sensor I had in my parts bin. Sensor is actually shorted when new. I believe that long pin gets worn and the conductors inside get cut thus opening the circuit. I wonder if your mechanic simply forgot to install them or did not connect them properly. Or maybe one is defective. It would be easy to take a look. But as I said, this should be his job! This is not rocket science!
 

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E63AMG, SLK32AMG, Ferrari 348 Spyder, R350 Bluetec, Eagle Talon TSI/AWD, Jeep CJ7, Smart EV
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300 Posts
Discussion Starter #7
Thanks to everyone that responded.

The solution turned out to be the simplest one: one of the brake wear sensors was defective. It had a break somewhere in the housing which made the electrical circuit open; just as if it had worn through.

So I replaced it and voila, instantly the annoying message on my display disappeared.

J
 

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2005 C240 silver, 2008 R320CDI Cubanite
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390 Posts
After how many clicks does the brake wear warning comes on?
That totally depends on your driving profile and style, as well as brake material I just replace the rear discs and pads on my R320 2008 after over 160K km. The fronts have been good since 70K km and will be good for a few more years. I stayed with OEM. But they come on with about 2 mm of pad left. So no big rush.
I check my pads twice a year when I change winter-summer tires. Or when you rotate them..
 

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1999 ML430, 2008 GL450
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I know old thread. I have an X164 (2008 - GL450). The above is likely the problem with my car; it's just got 15k miles on the pad and the sensor threw a code. Had the mechanic put the car on the rack and check all 4 corners; brakes & rotors look fine. Will grab a couple of these from the local Napa and have him replace both; as we couldn't tell which one could be malfunctioning.
 

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2008 AMG CLK63 Conv., 2012 R350 4-Matic, Wife's 2015 C300 sedan
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Just to throw my two cents in here.

The brake wear sensors have two wires running to contacts embedded in plastic within them. The sensors are triggered when the pads (and thus the plastic of the wear sensors) wear down to the point where the two wires feeding into / out of them created a CLOSED circuit (or short) through the brake rotor.

When I did my front and rear pads, front rotors only, job a couple of weeks ago, I used one OEM wear sensor for the front and an AutoZone wear sensor for the rear. I'm not sure if the fronts and rears are interchangeable. I didn't bother trying to figure it out seeing as they're only six or seven bucks each. You may also find the same wear sensors fit a multitude of different MB models of the same era. I can't see MB developing a brake wear sensor for each model any more that I can see them developing a new sump plug....

On my 2012 R350 4Matic gasoline model, there is one wear sensor on the front and one on the back, both on the right / US passenger / starboard side of the car. They simply clip into notches in the pads. Copy how they were fitted on the old pads and you can't go wrong.

You have to be careful when installing them not to chafe or bend the wires such that they come into contact with each other or short circuit. Although the wires are insulated, the insulation is very thin and probably quite easy to damage. If the wires DO short it has the same effect as the sensor contacts making a circuit through the brake rotor, so you'll get a false indication of brake wear. If you snap a wire either you'll get a short (and a false wear warning) or the sensor will never work at all.

Given the sensors are only six or seven bucks each, and given how they work, I would replace them every time I replace the pads. You can imagine, say, how water between the exposed contacts on an old, worn, sensor could create the same circuit as if the contacts were in contact with the rotor.

Once the pads and sensors are replaced the brake wear warning should disappear almost immediately. You might need to turn the ignition on and off a few times, but that's it.

Oh. 125K miles on what I think were the original pads and rotors, although I can't be sure because the car had 85K miles on it when we bought it. Front rotors were near worn out, but rears were perfectly okay to keep on using. I used OEM front pads and front rotors from genuinemercedesparts.com but el cheapo Bendix pads from AutoZone for the rears. Your fronts do 75% of the braking, so spend your money there and economize on the rears if, like me, you have to.
 
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