W124 and the abs light is on as many others I'm sure. I checked the front wheel speed sensors to see the resistance and they were ok, like 1500 ohms if I remember right. Where is the connection for the rear wheel speed sensors so I might check them? Is it on the frame rail underneath or some other place. Is there a connector on the module itself that I can pin out to check it there? Does anybody have a wiring diagram for that module?

Thanks

Kurt Kiefer

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

Found the connector for the rear ABS under the passenger rear seat. Does anybody have a FSM that tells what the resistance of the sensors should be?

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

Bump

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

I think the better test is to spin the appropriate wheel and measure for AC voltage at the connector.

I've found that my right front ABS wire/sensor fails this test, so I'm going to replace, but I hesitate at the price: $120 to 180, depending on where you get it. I'm very tempted to see if I can score a used sensor...

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Respectfully,
/s/
M. Dillon
'87 124.193 (300TD) "White Whale", ~392k miles, 3.5l IP fitted
'95 124.131 (E300) "Sapphire", 380k miles
'73 Balboa 20 "Sanctification"
Charleston SC

Let me pass on my very recent experience. My '87 has had an occasional ABS problem. The light didn't come on (except at start-up, yes the lamp works) but the ABS would cause the brakes to chatter at low speed -- a mechanic said that the "brain" was stuck in a self-test mode. He also said the right front sensor was bad. The front sensors are apparently the most failure-prone part of the system. Yes, they're expensive.

I checked the resistance of both front sensors, about 1000 Ohms. Then I checked the AC voltage from the sensor as you spin the wheel -- Maxbumpo has the right idea -- and the right sensor was low. The AC voltage from the sensor can be more than 1 Volt depending on how fast you spin the wheel. I suspect that tiny differences in the spacing between the sensor and the toothed wheel also affect this voltage; there is probably a factory spec. BTW, standard banana plugs fit the hole in the coaxial connector perfectly, also the outside ring, thus allowing you to connect your voltmeter hands-free without risk of damaging the connector.

In any case, I got most of the entire ABS system off of a 300E in the local Pick and Pull. I replaced both front sensors and my problem went away. I now have a spare "brain" and a spare pump. BTW, ABS sensors from other cars are similar but mount differently -- I initially bought a set from an S-class car but they won't fit the W124 chassis.

The factory has an (expensive, I'm sure) tester for the ABS system. Maybe you can find a mechanic who has one and will test the system, point to what is wrong. I've never seen a really good diagram of the internals although the FSM does have diagrams of a sort. In particular, there is no published diagram for the "brain" that sits up behind the battery.

Let us know what you find.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

Ok I'll do some digging. (I work for an abs company for a living) It should be noted that no or low voltage out of a WSS can be caused by a few things. If for some reason your tone ring is damaged it will provide an irregular signal and give a variable voltage for the same speed. If a sensor is gapped improperly it may not be close enough to the tone ring to sense it and will provide no voltage possibly giving you a false bad reading. Typically when testing ABS sensors the best way is measuring resistance. This tells you continuity of the coil pack inside the sensor as well as if there are any shorts or breaks. Thanks for your input guys, I hope to work on it some this weekend and i'll report back.

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

If all else fails, PM me, I should have a good pair of used sensors.

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Gone to the dark side

- Jeff

Not sure if I mentioned it before, but my idiot light is on all the time, right from the second the car is turned on. Typically (at least on the modules we design) the WSS won't cause a code until after the vehicle move and it sees that something doesn't jive. I have heard others say that a crapped out battery will cause a light and old fluid in the reservior will do the same. I have another battery laying around and I have some new DOT4 in the garage so I will try both of those first.

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

One of my '87s had a similar problem when I bought it. The sensors seemed fine, but the outer insulation was brittle and cracked in many places, so the easiest next diagnosis step was to install the two new ones I already had, the light and ABS have operated normally since.

Could be an intermittant short or open, which didn't manifest itself when checked?

Also, do you want me to check resistance on the rear ABS sensor? I have a good one on a subframe in the shop, ABS worked great when I last drove the car.

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Gone to the dark side

- Jeff

If you get a few minutes to run out and check that it would be much appreciated. There is a considerable amount of gunk around my rear sensor so i was unable to do a complete inspection of it. Do you remember what the fronts are supposed to be as well?

Thanks for your help

Kurt Kiefer

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

I checked it last night, didn't write it down, will do it again today (sorry). If my memory is correct (don't trust it), the rear sensor was 655ohms. I didn't have any probes with me so couldn't check the fronts anyway, will do so today.

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Gone to the dark side

- Jeff

ok my car got some love yesterday, but still no luck with the abs, here is what I have tried. Fresh fluid throughout and topped off reservoir. New battery, I heard it may help and probably could have used it anyway. Checked the resistance of both fron ones, they were 1600 ohms on the money. Gave each wheel a spin and they both seemed to make similar voltage. I removed them and cleaned off all the metal shavings, there was a considerable amount, but this didn't help either. Ideas, where to go next, pending checking the rear sensor with similar tests?

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

Does anybody have an extra brain laying around? I like to try one before I have to go to a junkyard and pay $$$ for it.

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2003 Dodge Ram 2500 Cummins - Georend fully built trans, Banks Big Hoss Bundle, Smarty Tuner, 5" turbo back exhaust. 500 HP and 1100 ft/lbs to the ground.
1979 Mercedes-Benz 300CD - Lost to a four car pile up on 275, Thank You Michigan Drivers.
1986 Mercedes-Benz 300D - Sold, Euro non-turbo car.

Have you checked your Overvoltage protection relay? I think if the fuse on the top of it is blown you will have an ABS light on all the time. Just a thought.

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Bill

Backyard Shadetree Mechanic, 30 years running.

1987 300TD
1988 300E (sold, sniff)
1999 S320
1981 Volkswagen Rabbit Truck (Diesel)
2001 Ford Expedition
1988 Suzuki Samurai
On my list to buy: R129, for me, and a R107 for my wife.

I have a complete working system, what numbers are on the brain?

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Gone to the dark side

- Jeff