ABS light permanently on. W123

[john_280TE]

My 280TE ABS light comes on when ignition is switched on, as expected, but sadly fails to go out. I understand ABS appeared on these models very late on, and my only manual.....the dreaded Haynes one makes no mention of ABS. I really do not know where to start looking to tackle this. (Similar problem on my everyday workhorse a Cavalier was easily fixed by replacing a connector under wheel arch) BUT, I don't recognise any ABS bits around the front brake calliper, where I would have expected to find something....................Help.

ps. Battery potential is spot on, and no brake lights etc are faulty.

Any help gratefully received.

 

[wireman]

In most cases either a wheel probe (2 front 1 rear) is dodgy or the over voltage relay is faulty.

Search this forum for more details.

 

[roofless]

as wireman say's the ovp relay. check the fuse on top if it's ok then it might be the relay http://cgi.ebay.com/ebaymotors/Merc...ptZMotorsQ5fCarQ5fTruckQ5fPartsQ5fAccessories it will look like this one

 

[john_280TE]

Thanks both. Also checked wireman's post of 20.08.07. Very helpful. And thanks for photo.
Can I assume that since ABS on W123 was a late addition, that is is the same as fitted to 124's? Will let you know how I get on.

 

[roofless]

it's in this link http://www.detali.ru/cat/oem_mb2.as....400&VIN=*&CT=F&cat=318&SID=54&SGR=045&SGN=03

 

[dazdread]

Any chance of an update of links

Hi there,

I have this problem and have no idea about where to start, any chance of an update to the links so I can have a looksee

 

[wireman]

Its Bosch 3 channel ABS2 on the 124 and 201 models, in the 1980's-90's Millers data (american models) that I have, the same system is used on all models listed with only minor wiring differences, sensor pulse rates may differ on some installations preventing just swapping control modules from different models. One day I may get round to drawing and posting a generic wiring diagram for ABS2.

John, the front sensor is on the steering knuckle behind the disk, just follow the cable that runs down from the top of the strut and its at the bottom end of it! The reluctor ring is machined radialy onto the inboard end of the hub and can in some instances become corroded to such an extent that the teeth shrink or disappear, an new hub is required to fix this but I've never seen one that bad.

Dazread, just search ABS, I don't have the time to do it for you, it would be nice if you post a list of the links you find, Ta.

BUT it's almost always the OVP to blame for your symptoms.

 

[dazdread]

Habe searched around and found plenty about W124 and others, I do not even know what the OVP looks like yet )

My ABS light came on about the time that one of the brake pads crumbled into dust.

Here are some of the threads that I have found.

http://forums.mercedesclub.org.uk/showthread.php?t=55175&highlight=w123+abs

http://forums.mercedesclub.org.uk/showthread.php?t=68724&highlight=w123+abs


http://www.benzworld.org/forums/w123-e-ce-d-cd-td/1478716-wheres-abs-controller-located-1984-w123.html

That is all I have been able to find, thin pickings.

Car now MOT expired and untaxed so need to fix this ASAP so would appreciate a check list of things to work through.

Thanks for all of your help guys

 

[television]

The OVP relay is the one with the fuse on top, only fitted to cars with ABS

 

[balge59]

Hi
this any help http://www.peachparts.com/shopforum/showthread.php?t=273893 ?

picture of W123 looks identical to W124 ABS here http://www.peachparts.com/shopforum/attachment.php?attachmentid=93040&d=1308285181

If the light started just after a pad crumbling try taking the wheel sensor out and cleaning it as the ring as already mentioned

 

[dazdread]

Again, any guidance appreciated. Will not be able to try anything for a couple of days... Will keep you posted.

 

[dazdread]

Just a thought, when the pads wear down which light illuminates. I have replaced all of the pads and two missing wear sensors but I noticed that many of the others were mashed.

Could that be it?

Mind you that would not account for the ABS not working when you slam on the brakes.

 

[television]

The brake pad wear lamp is not the same as the ABS one

Are you sure that you have ABS and that you are looking at the correct lamp

 

[dazdread]

Only mentioned it as the light came on when the pads crumbled but no other warning light came on.

I have a light with ABS printed across it that illuminates and I have some contraptions like the OVP under the bonnet.

 

[zeaphod]

abs light - my experience

I had a similar fault on a 97 w202.
the front wheel sensors are easy to locate - follow the cable to the hub, splined key to remove. Prise wire clip off joint under arch and gently prise apart.
The w202 sensors should read about 1000 ohms resistance. I'm guessing yours will be something similar.

The rear sensor is set into the diff. The cable joint is in the boot - easy to test the resistance. If the rear sensor is faulty it can be a bit of a pig to remove. I ended up drilling mine out after a few days of trying to haul it out.
I hope it isn't the rear, if it is try lots of releasing oil first before drilling. If you have to drill, look at the length of the replacement sensor and aim to drill in a couple of holes at the edge about 90% of the length of the sensor. That should allow the releasing oil to penetrate enough to release the old sensor.

 

[dazdread]

Checking sensors

Hi all,

Just resurrecting this thread. I have tried to measure the resistance on my front sensors yesterday. I tracked the cables up to a co-ax style connector under the bonnet.

https://www.dropbox.com/s/obj0586dcnftwff/photo 1(2).JPG?dl=0

https://www.dropbox.com/s/8kjo1nsl3y18c8u/photo 2(1).JPG?dl=0

I set my unit to resistance (the Ohm sign) and if I touch the probes together the reading goes to zero, if I touch them onto a metal bar the reading goes to .001 but on the sensors nothing, the reading remains as 1.

Am I doing this right or are both sensors nadged?

 

[television]

I do not know that meter, to measure the sensors I would set the meter to the 2kΩ range.

 

[dazdread]

I tried it on every setting in the end as electrics are not an area I am overly familiar with.

 

[television]

If the meter is set too low a range it will read nothing, test it on a light bulb



I know its easy for me as I have been doing it since 1947

 

[dazdread]

On a light bulb it goes from 1 displayed on the left hand side of the display to 108 on the right, the other settings of 2 20 & 200 just move the decimal point along.

So the question, is am I checking in the correct place and if so are both of my sensors nadged?