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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #1
Hey guys...

This week I tried to see if I could find the fault in my speed sensor.. I have the ABS light from the second I start moving after starting the vehicle. When a small diagnosis was done with a STAR system, it was said that the front right speed sensor is faulty..

So this week I took it off from behind the wheel, cleaned the magnetic sensor, and also the other black piece next to it.. Still no changes... Next I will check the upper connections, make sure there is no dirt preventing connection..

My question is... Is there anyway to repair, find fault, or to service the speed sensor? I saw one on E-bay for about $200 with shipping, but If I can rather try fix mine I would do that first. Otherwise I will have to visit my local breaker and see what prices they give me...

So please dont respond by saying "Get a new one" or "Visit the STEALERSHIP" or just "Replace it"

The topic of this thread is to find methods of repairing this device.. Please any input regarding that will be useful!!! I will try it out and post the results...

Thanks in advance fam
 

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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #2
In the pic below, I circled the 2 pieces of the speed sensor that are situated behind each front wheel.. These are the 2 pieces I tried to clean / service... Next I will attempt the top plugs that plug into the ABS module...

So anybody with any information that me help me in this endevour, please share it with me!!

Thankx
 

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Dont see how. It is a sealed solid state unit

It detects wheel movement by proximity (sonar if you will) of notches @ hub
 

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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #4
Dont see how. It is a sealed solid state unit

It detects wheel movement by proximity (sonar if you will) of notches @ hub
hmmmm.. I see... Thanks for the input..

Are you sure it is sonar and not magnetic? That silver piece thats been circled was magnetic.. Though im DEFINATELY no expert in this field..

"Notches" you say? what happens if those notches get very dirty, can this cause the sensor to not pick them up? When I pulled the the little silver cylinder out, the tip was VERY dirty.. (Was hoping a simple clean would do the trick but it didnt)

So what if I strip the hub, would I be able to get to those notches? Im really not too keen on replacing my speed sensor, I see no reason why it should be mulfunctioning, so I want to try EVERYTHING else besides replacing it first, only if all the methods still dont take away that ABS light, then I guess I will have no choice..

But if I could just fix this prob with spending almost nothing, or nothing then Ill be very happy. Atleast the money can allocated for other more serious repairs on my list..
 

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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #5
also, what on earth is that black piece that attaches to the brake caliper? (Also within the red circle in the pic).. I would imagine that the silver cylinder is the actual sensor that detects speed, but what is the purpose of this black piece? Its connected by one bolt to the brake caliper..

(I know its not a brake sensor - thats completely different)

It has two holes on each side.. each hole a little rod inside. One of the little rods is broken in mine (atleast it seems so) could that be a contributing factor as to why its mulfunctioning?
 

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hmmmm.. I see... Thanks for the input..

Are you sure it is sonar and not magnetic? That silver piece thats been circled was magnetic.. Though im DEFINATELY no expert in this field..

"Notches" you say? what happens if those notches get very dirty, can this cause the sensor to not pick them up? When I pulled the the little silver cylinder out, the tip was VERY dirty.. (Was hoping a simple clean would do the trick but it didnt)

So what if I strip the hub, would I be able to get to those notches? Im really not too keen on replacing my speed sensor, I see no reason why it should be mulfunctioning, so I want to try EVERYTHING else besides replacing it first, only if all the methods still dont take away that ABS light, then I guess I will have no choice..

But if I could just fix this prob with spending almost nothing, or nothing then Ill be very happy. Atleast the money can allocated for other more serious repairs on my list..
i just said sonar cause it was how the sensor works. detects distance between points in a 1 0 fashion. dip 0 ridge 1. it doesnt use actual sonar technology no (would be v cool if it did). just the same principle of bouncing a field to detect changes in terrain :eek:

these things fail all the time. mercedes has replaced the parts with an improved version.

140 540 28 17 > 140 540 34 17 pre 96
140 540 29 17 > 140 540 35 17 96 and up

so technically getting the new version should fix you up for a long long time.

normal rust build up on the hub won't cause it to malfunction. and dirt shouldn't be an issue either unless you regularly offroad the car in spindle deep mud (doubt it)

i advise against taking the hubs out just to look - you will need new bearings and seal rings if you do this.
 

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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #7
i just said sonar cause it was how the sensor works. detects distance between points in a 1 0 fashion. dip 0 ridge 1. it doesnt use actual sonar technology no (would be v cool if it did). just the same principle of bouncing a field to detect changes in terrain :eek:

these things fail all the time. mercedes has replaced the parts with an improved version.

140 540 28 17 > 140 540 34 17 pre 96
140 540 29 17 > 140 540 35 17 96 and up

so technically getting the new version should fix you up for a long long time.

normal rust build up on the hub won't cause it to malfunction. and dirt shouldn't be an issue either unless you regularly offroad the car in spindle deep mud (doubt it)

i advise against taking the hubs out just to look - you will need new bearings and seal rings if you do this.
NICE!!!! Thanks for that, was exactly what I needed to know..

hmmmmmm, lets see...The part of the hub where the silver cylinder was connected to is EXTREMELY dirt.. The sensor had this black gunk on it, almost looked like used motor oil..

Funny you should mention offroad.. That is quite a possibilty because the vehicle was licensed in "Freestate" when I first got it. Now Freestate is a very DRY place, very arid, almost like a desert. So there are MANY non-paved roads there. For all I know offroad could have been part of the previous owners daily commutes.. I do know for sure there is a hell of a lot of pot holes there, and they must be huge..

Because when I first got the car, half of the exhaust was missing, the petrol components cover was missing, both rear inner wheel well linings were damaged.. Clearly it took a few hard knocks on those poorly maintained roads..

So back to the topic at hand, is there any way to clean that part of the hub which the speed sensor uses to do its readings? It would look like "teeth" of sorts, am I correct?

Im really determined to fix this prob however way possible without replacing the actual sensor itself..
 

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It's probably bearing grease (weak/busted seal ring) mixed with brake dust and baked on by heat.

Yes it's literally lines of metal.. i just looked and for some stupid reason never took a photo of the back of the hub. Who thought would ever need one right hah

no way to clean it without pulling the hub off (it's easy, putting it back on though could be tricky)

the circled part is where your speed sensor is poking from. you also see the bearing/hub retaining nut with the tightening screw on the side.

pry cap off, loosen screw on the retaining nut and then remove the nut thing. front bearing will pop right off, then pull hub off and rebuild as needed.
 

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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #9
It's probably bearing grease (weak/busted seal ring) mixed with brake dust and baked on by heat.

Yes it's literally lines of metal.. i just looked and for some stupid reason never took a photo of the back of the hub. Who thought would ever need one right hah

no way to clean it without pulling the hub off (it's easy, putting it back on though could be tricky)

the circled part is where your speed sensor is poking from. you also see the bearing/hub retaining nut with the tightening screw on the side.

pry cap off, loosen screw on the retaining nut and then remove the nut thing. front bearing will pop right off, then pull hub off and rebuild as needed.
YOU ARE THE MAN!!!!!!
Thank you my brother, you pretty much summed everything up for me.. I understand it much better now, and will contemplate which is the best way to go about fixing this problem..

Will let you know if there was any success..

(Oh by the way, do you know what that black piece is? the one I mentioned above also in the red circle on my pic? Does it have any functionality and what could that functionality be?)

THANK YOU Gyrate, you are a good person..
 

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2008 C200K (W204) & 1998 SL500 (R129) Imperial Red
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Discussion Starter #11
re that thing: brake pad wear sensor plug
are you 100% shure thats what its for?

I thought the brake pad wear sensor was the wire which connects directly to the top of the actual brake pad? It works like a switch, where upon contact (from pads worn out) it lights up a warning light in the cluster.. I broke mine on my BMW when I was changing brake pads, and ever since then the brake pad was constantly on.. thats why im questioning what that black piece is for, because I was quite sure the brake pad wear sensor was not that. Its connected to the outer part of the caliper..
 

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1986 560SEL, 1986 560SEL, 1992 500SEL, 1999 S500
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The sensor is nothing more than a coil of wire wound on an armature and is almost impossible to go bad. What does cause the problem is the wire going from the spindle to the fenderwell--it is constantly flexing and twisting and the inner conductors will break. They may have an intermittent connection. You can measure the resistance of the sensor with an Ohm meter at the connector--just don't measure on the pins for the wear sensor. You should have about 1,000 Ohms with a steady reading. As you observe the meter, move the cable all around and I bet the readings will fluxuate wildly, indicating broken conductors,
 

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are you 100% shure thats what its for?

I thought the brake pad wear sensor was the wire which connects directly to the top of the actual brake pad? ..
correct and this is where the sensor plugs in on the other end.

the whole reel of wiring is #5

the actual speed sensor part is 19 and 18 is your brake wear subharness.
 

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