So the earlier this week while driving on the highway, I got the pop up message to check brake pad wear on the center cluster. Since I have my annual service coming up in a few weeks, I figured I would just wait until then. In the meantime, I did a visual inspection of the outer pads and both axles appear to have some meat left on them. The front brakes were done about 5 years, 44k miles ago and the rear brakes are still original so it could be time.

However, in the two days since the message appeared, it has not reappeared and I've done plenty of driving/braking since then. What's the logic behind this message? I understand there is a wear sensor (one per axle IIRC) and when the contact is triggered you get the message. I thought the message would persist with each trip, but it hasn't reappeared. Could it be a sensor issue or does this warning not nag you like others?

 

For starters, the warning always gives you plenty of time to take care of pads replacement.
I don't wear pads fast, so did not hesitate to make 3000 miles before actual replacement on older cars, where sensors have been over 2mm before the pad end.
Now W212 suppose has newer system that I did not explore far yet.
The sensors are at 50% pad thickness and computer calculate when it is time to replace- based on your driving habits. That could explain the intermediate warnings.
Don't get me started what I think about software programmers who drive the cars on computers, but not in real life.
But whatever it is, don't ignore the issue for long time.

 

It might be an intermittent issue due to poor contact between the sensor pins, clipped wires or any other sort of bad electrical connection which isn't fully dead yet. Or it could be a preventative maintenance message although I'm not aware of MB vehicles doing that. On my E60 BMW I remember having a certain number of miles on the IDrive system before the car would tell me to take a look at the pads( I think the initial value was around 30k miles and then it would go down with driving) and it also did the same thing for the motor oil. I've yet to see a warning on my W212 for brake pads, but I would think it should be red or amber if the actual wear sensor is worn out.

 

It’s probably your rear pads. If I remember correctly, the sensor is on the inboard pad, so you may not be able to see how worn it is. Maybe pull the wheel and inspect.

 

This was my thought as well. In my past posted brake job, all corners looked ok except for one inboard pad. Worth taking a closer look.

 

Yep, mine were the same way, the one that was the most worn was the inboard pad with the sensor on it. The other 3 had way more meat and the outboard ones looked fine. I think you can use Akebono on your rears. They've been great for me, no dust.

 

Thanks for the input. I will get the inboard pads checked at the next service opportunity. Still seems strange that the message would appear on trip and then not reappear on subsequent drives.

I have read good things on the forum about Akebono pads and Centric rotors. Those are on my list for the next brake job. Don't care for the shimmy, squeaking and brake dust of OEM.

 

Mine was exatcly like this, I changed the front, lights still on, take the rear left wheel off, looks good, take rear right wheel off, inner pad is eaten away. such bs. All my pads were ok even the right rear wheel outer pad. faulty calipers, system designed to eat away that one caliper? maybe. Wish I had asked this earlier and before I returned my leased car. wasted money and time.

 

Is there light that comes on to indicate brake pad sensor is triggered? All I saw was the message posted above on the center cluster - click OK on steering wheel and it went away.

 

When mine came on, I had to guess. I knew the fronts had been done recently so when I looked to the rear, found the pad with the sensor had been worn down. I didn't use a code scanner, so I'm not sure if there would have been a more specific MB code that would have told you which sensor it was.

 

Still waiting on my next service but the warning popped up again this weekend after about 10 days and again today, 2 days later. Seems sporadic.

 

We are still waiting for final update?
From what I've seen "somewhere" MB incorporated new feature in those cars.
Now pad sensor is not 2 mm from pad end to trigger instant warning, but it is more like 4-5 mm and when sensor wears, the computer is calculating how much pad you have left base on your driving style.
Sounds exciting, but how much of that is myth?

 

I actually started another thread about the brake job but didn't come back to update this. When I took the car in for service in December 2017, the dealer quoted me on a brake job and said that there was 3mm left on front and 2mm left on back. I wanted to shop around for a better price and the warning came up occasionally for a few months but then started showing up each time I started the car. Got the brakes done in June about six months after the first warning. I didn't ask how much was left but I figured when the warning came on regularly it was time.

 

Will checking the sensors ohms reading work? Compare the reading of all sensors with a new one.

 

A visual check is all you need. The sensor is a small stick inserted into the pad and when it makes contact with the rotor it provides the warning and is then destroyed and must be replaced with the new pads.

 

yep, very simple system on a loop. if the sensor wire is broken, or bare wire makes contact with brake rotor, light will come on. I'm guessing you are just at the sensor level of the pad and barely worn through the wires insulation, causing intermittent contact.

 

Yes, the plastic shaft of the sensor is not a press fit in the hole in the pad, so it can wobble around a bit (intermittent closed circuit) until the pad surface wears more for more solid electrical contact between sensor wire and the steel rotor. I've had this happen with my older MB.

 

So the W212 doesn't tell you front or rear? Even my W203 would specify, I think?

 

Newer tried to check it with advanced scanner, but being more mechanic than "technician" it is easier for me to spend 90 seconds to take the wheel off and see, than 20 minutes on trying to figure out the scanner.
I confirm that when older cars had sensor touching ground at rotors, W212 do have wire loop that wears open.
Bad part, I usually could reuse older sensors even with some wear, when new sensors are not-reusable when they come to the end. .

 

no it doesn't, and no it didn't.

 

Having owned 3 of them, I can confirm that the 124's just lit a light on the dash, there was no way to tell which sensor. when the pads are starting to get close to worn, the light would come on intermittently with brake application, and as they approach fully worn out, the light came on solid when you step on the brake.

 

Here u go............ close up look


Simple estimate.
Backing plate if 6.1mm + adhesive and spike to attach friction material to backing plate assumed as 2mm total 8.1mm as max worn out limit.
So 8.1mm or 1mm of pad friction life from 9.1mm with alarm constantly triggered, that is easy decently driven 3,000 - 4,000KM useable kilometers more to go.
So far, based on my front brake pad consumption, I am getting 3,400 to 4,600 KM per mm consumed.