w201 ABS light on

[lsmalley]

Did a search and couldn't find anything that I haven't tried short of replacing major components. My ABS light is on and I have done the following:
1.) Swapped out OVP: did not help
2.) Swapped out black BOSCH relay under ABS casing: did not help
3.) Swapped out metal relay under ABS casing: did not help
4.) Cleaned both magnetic front ABS sensors: did not help

Any suggestions?

[Gilly]

Does the abs work or not? Try locking up the brakes on gravel or something to see if it works. There is also a rear sensor (on this model i think it's just one, on the differential), but at some point it will be time to bust open the books and start actual testing instead of testing by substitution.

PS the normal problem with the front sensor is in the wiring

[lsmalley]

I'd rather not try to lock up the brakes on gravel, I don't want to get a ticket for reckless driving....what I did do was jack up the rear wheels and get them spinning at about 20 mph and depress the brakes and there is a pulsating feeling on the pedal that does not allow me to fully depress the brake it feels like. So I'm guessing that is the abs system working, correct? I had that same pulsating when I was caught in a random snow storm driving up a mountain when I tried to brake. If the abs is working, could there still be fault with the wiring?

[JamesDean]

When does the light come on? Immediately when the car is started and you're still in park?

Or after you start going forward?

You might also need to clean the gearing area that the abs sensor "reads".

[Gilly]

I would say the abs works, not sure though, if you are only testing the rear wheels. In this case it might be hard to tell if the system is fully functioning even on gravel. You could try a panic stop in a parking lot in the rain. I never am overly concerned about reckless driving tickets if I am testing a car, just find someplace out of the way to try stuff and BE CAREFUL no one is behind you or around at all, such is life in Cali I guess that you have to worry about this.

One thought also is since warning bulb sockets can inadvertantly put in to incorrect holes in the back of the dash, make sure the bulb socket is in the correct hole, you may have a different problem than you think. Holes are numbered and the socket wiring should have the same number.

[lsmalley]

Abs light comes on after I start driving. Yep, I checked the light socket numbers and it is number 4, which corresponds to the abs.

[JamesDean]

That what our 420SEL did. I had the shop clean the sensors and hub/gear area and that fixed the problem. Give your another cleaning and be sure to hub/gear area too. Maybe that'll do it.

[lsmalley]

What do you mean the hub gear? where can I gain access to that?

[Gilly]

He means the part you see if you take the abs sensor out, there is a toothed ring, called the stator, which is what the sensor is actually sensing, it makes the sensor produce a sine wave that the abs computer processes into the wheel speed. If the stator gets too crudded up it can make a "ratty" signal for the sensor.

edit, probably not the best example, but this shows what the abs sensor is pointing towards, I think it is just a machined part of your hub, not a seperate part:

[JamesDean]

I think you can just remove the sensor, spray into the hole and rotate the wheel while doing it. I think that would clean it?

You want to clean the geared part on the hub:
http://www.peachparts.com/shopforum/diesel-discussion/320999-w124-front-axle-bearing-spindle-damage.html

Kinda hard to get your bearings in that image..

[JamesDean]

Originally Posted by Gilly

He means the part you see if you take the abs sensor out, there is a toothed ring, called the stator, which is what the sensor is actually sensing, it makes the sensor produce a sine wave that the abs computer processes into the wheel speed. If the stator gets too crudded up it can make a "ratty" signal for the sensor.

I think in this case it would be called the rotor? as it rotates? The sensor would be the stator aspect?

[Zulfiqar]

Ive always been told its called a tone wheel. Ive done this cleanup on my car front wheels when it illuminated the ABS lamp.

I was set to do wheel bearings in the next week - so it was a in place job.

[Gilly]

Well there are different names used for the same thing, in my neck of the woods or the guys I've worked with, we always called it the stator, never the rotor, that would be confusing since the brake rotor is nearby and I don't think it's the correct term, I think the abs system uses terms also used in electric motors, but this is not an electric motor, it is a speed sensor. Anyways here is a link that describes the basic parts and they also say there are several terms for the same thing, never mentioning "rotor" as a description (which is why I chose it, LOL)
http://www2.vsm.skf.com/~/media/Files/enUS/Automotive/457102_07_09_16_22.ashx

[lsmalley]

Thank you all for the help. Fortunately for me I live in a climate where I only get about 5 inches of rain per year (maybe rains 15-20 days a year at the most) so for now I will just remove the damn bulb so the ABS light doesn't continue to light up my dash. I will have another look at the sensor, I did notice that the wiring sheath on the passenger side is frayed, but there does not appear to be any damage to the wire that I can see.

[Gilly]

That's probably the problem, there is a flow chart you need to follow to diagnose early abs without stored codes. Usual abs sensor problem is with the wiring in front due to the wheels turning right/left.