fnasser1

2016 GLE400. Brake sensor has never properly functioned. Have no indication of wear on pads. Recently told I need new pads and discs for front. Could not get answer from service center why there has never been a message or warning that pads were worn. Have no idea how to check for 'pad wear or replacement' on control settings. Can anyone advise?

ddeliber

The brake sensor is not a gauge that reads pad life, it is a single indicator sensor it only triggers when the pads are worn to the point at which the sensor touches the rotor. In fact the act of triggering kills the sensor - one use only. You likely have pads worn almost far enough to trigger the sensor but not quite there yet.

fnasser1

Thank you for your response. I understand the concept behind the sensor and how it works. What is not appearing on my 2016 GLE400 is any indicator that the pads have worn, in essence that the sensor had determined that the pads are worn and now a digital indicator shows it is time for pad replacement. One would assume this is automatic, but at least appears under the "Serv" heading on the digital control panel. It does not and I don't know why.... appreciate the input.

ddeliber

I am pretty sure that there is no menu item under service or any thing like that, you will just get a warning indicator when the sensor triggers. It just hasn't gotten there yet. Something like this:

It is possible that the sensor (only one per axle front and back) is installed incorrectly and this won't show up, but not likely, they are pretty easy to put in. How do you know that you need brakes? is it squealing or scraping? Metal on metal sounds when you brake? Anything like that?

fnasser1

Thanks again for the quick response. That's what I figured and Mercedes said. I just read in one of the responses that there is only one sensor front and back and if the pads wear unevenly you may never get a warning until it is so bad that the disc becomes warped or scraped. That is what happened to me on the back brakes and apparently is occurring on the front. During a recent visit to Mercedes to correct a recall item (drain plug in spare tire well), I was told that front brakes and discs need to be replaced. The car has 51K miles and it is mostly urban/suburban driving...lots of braking. I guess my biggest bit of confusion is how come I end up needing pads and discs everytime? That is quite expensive as you know. I could understand the need to replace a set of pads depending on driving habits and mileage, but discs too?? That usually points to excessive wear on the pads, at least in vehicles under 50k. There is no noise, no squeal, no vibration, no other physical indication of brake pad wear or disc damage. The timing is probably right, and the driving habits also, for front brake pad replacement, despite the absence of any sensor indication. And I suppose that goes for the discs too. Appreciate your input and knowledge on the subject.

ddeliber

AAhh, Now I understand. You are likely suffering from the common affliction known as Dealerassphincterpreparitis. It is often accompanied by acute headaches and an uncomfortable sensation in the gluteus area.

Sorry, I couldn't resist, and yes I just made up that word, but it should be a word because that is what it is "prepare yourself and grab your ankles".

Dealer service advisors get paid on how much they bill not much more to say than that.

I have yet to find a dealer in the last 20 or so years actually measure a rotor's thickness before they replace them. If a customer asks for brakes, they always replace the rotors as well. Some of this has to do with rotor design (they are a bit thinner than they used to be - they say it is to save weight) but mostly it has to do with money. Don't get me wrong, dealers will resurface routers and only replace brake pads but this only seems to happen when they are prepping a car for sale. I have seen it in the reports for prep work on cars for sale. Some dealers are up front about it and simply say "we don't resurface rotors". There is a measurement in the book for minimum rotor thickness most if not all just don't even check unless they are paying for the parts.
In addition, many SAs have a loose definition of the word need. As in you "need" brakes. I think the min pad thickness is around 3.2mm but 4mm is common. This is around where the sensor is set to trigger. Just so you know new brake pads are 11 - 12 mm thick. A good SA should say something like "you have x% life left in your brake pads". Many just say you need brakes - and I wouldn't be surprised if the threshold some of them use is less than 50% - some unscrupulous ones don't even check, they just always say you need brakes if its been about a year or so since your last brake job.
Measuring pad thickness is simple, tons of videos on youtube will give you an idea if you want to check for yourself (Inside pad thickness measurement is a bit of a pain). If you are not interested in how this works or you don't really care to do it I recommend that you take it to a tire shop or an independent mechanic and ask them how much life you have left in the pads. Probably worth the effort just to see how trustworthy your SA is, if he/she is reasonable you can decide to believe him/her for future work.
Brake job cost is a totally different topic for another time. You can decide cost vs value but it is a good idea to at least check at least once to see what you are dealing with.

mikapen

​​​​​​The best way to determine if pads or rotors need to be replaced is measurement, not a sensor.

I would definitely trust the dealers measurements - sensors, noise or scraping only alert you 'after the fact."

Did they provide measurements? They should. My shop notes pad thickness at every service.

And I can get an idea of disc wear by looking at the ridge remaining at the circumference, where the pads don't touch, so visual inspection is a good starting point.

Back in my BMW days (late 80s) their rotors wore out before the pads. 30,000 miles was about all anybody could get.

fnasser1

Thanks for all your input. Sensor or nor sensor, I am inclined to follow the old standards for replacement of mechanical parts like brake pads and discs. As for "Dealerssphincterpreparitis" and because of my background in the healthcare field, I always get a second opinion...

ddeliber