DIY - Replace Front Right Speed Sensor (ABS light) - Tutorial with Pictures. - Mercedes-Benz Forum
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post #1 of 12 (permalink) Old 05-03-2011, 01:53 PM Thread Starter
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Arrow DIY - Replace Front Right Speed Sensor (ABS light) - Tutorial with Pictures.

Hey guys..

Replaced my front right speed sensor, bought a replacement at a local Mercedes breakers for $65.

(I knew my front right speed sensor needed to be replaced because my "ABS" light was light up on the instrument cluster every time I would start the car. Had a STAR dianosis done on the vehicle, and it said the front right speed sensor is faulty.)

It is very easy to replace the speed sensor, infact I did not even bother taking off the wheel. (Though it would be easier to do this job with the front wheel off, and car supported on PROPER heavy duty car stands)

Step 1. Get a replacement speed sensor, part number on the wire.

Step 2. Remove protection cover of wire harness on right hand side. (3 turn clips)

Step 3. Unplug speed sensor from plug in wire harness. (right circle on picture 3)

Step 4. Unclip protective cylinder near ABS module, then unplug speed sensor cylinder plug. (left circle on picture 3)

Step 5. Push the wires with the rubber "plug" down into the wheel well. (picture 4)

Step 6. Unclip wire from clip holding it to the inner wheel wall, use flat screws driver. (no pics)

Step 7. Unlcip sliding clip 1. (no pics)

Step 8. Unclip sliding clip 2. (Arrow on picture 5)

Step 9. Remove 2 bolts (Allan key) for speed sensor head. (Right circle on picture 5)

Step 10. Remove 1 bolt (10" socket) for brake wear sensor. (Left circle on picture 5)

Now that you have removed the speed sensor completely, just repeat steps in reverse when fitting the new / replacement speed sensor. Take a look at picture 7, that is what the speed sensor looked like which i removed from my car. It possibly could have been repaired by reconnecting that yellow wire, and re-insulating it. This was poorly repaired by one of the previous owners, but broke again. So it is best to replace the whole thing anyway.

If you break any clips, you can also use cable-ties to secure the wire place, dont use electrical tape.

Since I replaced my speed sensor, the "ABS" light no more comes on. But now the "Brake Replace" light replaced it lol.. I was going to change my brakes soon anyway, so Im sure that light will disapear after that is done.

Unfortunately my Cruise Control did not return Though my front tirews are different from the back ones, so once I replace those and fit the correct size Im hoping that feature will be restored..

Hope this helps atleast some one out there..

Regards
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4liter and Charence like this.
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post #2 of 12 (permalink) Old 05-03-2011, 06:33 PM
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on a related note, i rewired my CD player (potential fire hazard), and my ABS light went out. must have been a stray wire grounding that controls the volume from your speed sensor, im guessing. my cruise control still isnt working either.


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1992 300SD
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post #3 of 12 (permalink) Old 05-03-2011, 06:42 PM Thread Starter
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interesting... Have you had the car diagnosed by a STAR system yet?

My Cruise Control is also not restored yet, Im hoping once I match all the tires it will "work again"
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post #4 of 12 (permalink) Old 05-03-2011, 07:01 PM
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Quote:
Originally Posted by MafiaDON View Post
interesting... Have you had the car diagnosed by a STAR system yet?

My Cruise Control is also not restored yet, Im hoping once I match all the tires it will "work again"
havent had a diagnostic done yet. that will be the next thing i do...


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post #5 of 12 (permalink) Old 05-03-2011, 07:42 PM Thread Starter
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Originally Posted by bmwsucks View Post
havent had a diagnostic done yet. that will be the next thing i do...
lol, yes its best you do that comrade..

I found out about my front right speed sensor being faulty just by a "short" STAR diagnostc run..

I cant imagine what I will uncover when I get the extensive one done on my car.. Definately a MUST especially if you dont know your cars history before you came into the picture..

Goodluck with that my friend
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post #6 of 12 (permalink) Old 05-17-2011, 07:33 PM
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The faulty brake light switch will always set off ABS. In fact, I've gone through 3-4 of them in the last 11 years with one of my 140s. Until I forced myself to quit buying cheap Chinese ebay units and go pay the dealer.

Sometimes if you set a light object in the pax seat (bag of grociers) will set off ABS from the seat sensors. And you'll play hell trying to find the fault lol. A laptop - especially running - will also cause enough EMF interference to set off ABS from the pax seat.

Just a few ideas for future use - I saw you had already pinned it down the the speed sensors - congrats

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post #7 of 12 (permalink) Old 05-18-2011, 12:49 PM Thread Starter
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Originally Posted by geebee View Post
The faulty brake light switch will always set off ABS. In fact, I've gone through 3-4 of them in the last 11 years with one of my 140s. Until I forced myself to quit buying cheap Chinese ebay units and go pay the dealer.

Sometimes if you set a light object in the pax seat (bag of grociers) will set off ABS from the seat sensors. And you'll play hell trying to find the fault lol. A laptop - especially running - will also cause enough EMF interference to set off ABS from the pax seat.

Just a few ideas for future use - I saw you had already pinned it down the the speed sensors - congrats
Yes, I have heard that a faulty "brake light switch" could cause the ABS light to pop up, but in my case it definately was the "Speed Sensor", front right to be exact..

Best way to figure out the root cause is to get an extensive diagnostic done on the vehicle, from there you will know which parts need attention..

Cheers comrades
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post #8 of 12 (permalink) Old 10-01-2011, 05:14 PM
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Smile Replace ABS Sensor

Replacing the front ABS Sensors on a 2001 S430 is about a 10 minute job; rated 1 on a scale of 1 to 10. Removing the wheel is not required, but makes the job easier. With the car on jack stands for safety, simply remove the ABS Sensor from the back of the Hub using a T-50 Torx. Remove the Sensor wire from two or three rubber retainers holding it in place, following the Sensor wire up to the wheel arch. Remove the wire clip holding the Sensor wire connector in place. Unplug the Sensor wire connector along with the airmatic shock connector (they are snapped together as a unit). Installation is the reverse. Your alerts should reset if the ABS Sensor was your only problem. If you accelerate past 35 mph with no failure lights, you've fixed your ABS Sensor.

Last edited by LLJ20024; 10-01-2011 at 05:25 PM.
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post #9 of 12 (permalink) Old 10-01-2011, 10:43 PM
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MafiaDon:

Excellent writeup. Allow me to add a Machiavellian element to your story.

I just repaired my left front wheel sensor (95 S320). The dealer wanted $422 for a new cable so that motivated the repair. During the repair I did some analysis. The fault mechanism appeared to be a break in the wire leading to the wheel sensor. This was caused by metal fatigue occurring at a point where the cable bends as the steering is turned back and forth.

Since the wires are multi-strand copper and have stress relief mounts molded into the cable assembly, I was curious as to the reason for the break. Upon closer analysis, the copper wire strands appeared to be uncommonly stiff and brittle. Ductility was very weak. They were also difficult to solder. The same could not be said of the brake pad sensor wires. They were extremely flexible.

For those who may be interested, copper wire is usually formed by a cold draw process (which leaves it brittle) and then annealed, which provides it with good ductile properties. Based on my limited sample (sample size =1), I would guess the copper was contaminated at some point during manufacture which caused a change in its physical properties. It did not seem plausible that it was improperly annealed although that is not out of the question. Investigating further, I discovered Mercedes did a running change on this harness after 95. The ONLY change was to separate the harness into two harnesses, one for the brake pad sensor and one for the wheel speed. All the fittings and connectors remained the same. This would have added cost to the assembly so my suspicion is Mercedes covered their tracks with this change.

With all the problems Mercedes had on the engine wiring harnesses, this appears to be another harness quality problem that got by the qualification and quality inspection group. IMO, whoever was heading that group up at the time was completely incompetent or corrupt.

1995 S320 -- built like a tank.


Unfortunately, tanks break down a lot.
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post #10 of 12 (permalink) Old 10-02-2011, 04:07 AM
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The wire simply broke from use!!! Nothing lasts for ever. Any metal which bends goes through a process called "work hardening", which means as it bends the proprties of flexibility change--the wire gets stiffer at minute points and eventually breaks. As far as separating into two harnesses--it is cheaper to replace only the one that broke, They will not both fail at the same time.
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