ABS problem

10 replies [Last post]
DutchG
DutchG's picture
Offline
Joined: 07.02.2008
Location: The Netherlands

My 1992 300GD (463) is equipped with ABS. It's worked fine until a few days ago when it started engaging for no reason at all. On moderate braking I sometimes get the typical pedal-pushback and diminished brake performance. Checked fluid level and brake pads: level is fine, pads are close to minimum but nothing scary yet. No problems and normal brake performance with ABS disengaged. Any ideas?

DutchG
DutchG's picture
Offline
Joined: 07.02.2008
Location: The Netherlands
Re: ABS problem

Quess I'll have to answer my own question. Had the dealer check it this morning. They said it's a wellknown problem with older cars with ABS: corrosion of the mass-connection on the wheelsensors. Their cleaning job should fix it. Wait & see ...

M2dxb
M2dxb's picture
Offline
Joined: 27.06.2005
Location: UAE (Dubai)
Re: ABS problem

Thanks for the follow up, useful to know!

jantie
jantie's picture
Offline
Joined: 09.02.2013
Location: Mallorca, Spain
Re: ABS problem

  Hi Marko,

I have a 300 G D cabrio 1990 and i have the exact same problem with my G. When the ABS is switched of i can brake normal, without ABS. If i put the ABS switch on, the pedal gets hard and pulsates(that sounds kinda dirty, lol) and braking is almost impossible unless you take your foot off and brake again.
Mercedes checked the whole system and they said, after paid 300 euro for a simple job, that i had to change ALL the sensors. Costs around 2000 euro. I cant believe that because of a faulty sensor the car gets so dangerous that you can not brake. It has to be something else. Did you ever find out what the problem is? I want to find it out because i restored the cabrio to almost new and want to keep it till they can bury me in it.

Thanks,

Jantie

Pistonhead
Pistonhead's picture
Offline
Joined: 16.12.2006
Location: Loughborough
GWOA Groups: Committee, Members
Re: ABS problem

For all sensors to fail in one go sounds very dubious! You would have the ABS light coming 'on' should a sensor have failed. The fault you are describing can occur for several possibilities, without ABS light coming on.

Brake fluid for one; this needs to be renewed every two years and if not, you can get brake fade which is brake losing its affectivity under prolonged braking. In the worse case scenario brakes can totally fail; ABS or not. From your quote "and braking is almost impossible unless you take your foot off and brake again."  I take that to mean at the first brake application the pedal is soft and also pulsates, at the second pedal depression the brake are fine; this condition may also occur when the brake fluid is old. Renewing the brake fluid can resolve the issue.

There are other reasons for a pulsating pedal but these are without a soft  pedal and I feel . Your issue with a soft pedal is brake fluid related. Developing on my line of thought, if it is brake fluid to blame, why then is problem resolved renewing the sensors? I do not know.

I am not in the mood for deep thinking at present.

bigblock
bigblock's picture
Offline
Joined: 27.05.2009
Location: HIGHLANDS
GWOA Groups: Committee, Members
Re: ABS problem

  Hi Jantie

Instead of resurrecting three old threads on this subject you would be better served by creating a new topic so that any assistance from members can be concentrated in the one thread.

Ford Prefect
Ford Prefect's picture
Offline
Joined: 14.11.2006
Location: Scotland
GWOA Groups: Members
Re: ABS problem

 This can also be caused by a build up of dust in the rear drums.   If it goes to one side from the front on braking it's a caliper sensor.   If the back slides out it's the rear brakes.

JASONGDS
JASONGDS's picture
Offline
Joined: 15.07.2011
Location: High Peak
GWOA Groups: Members
Re: ABS problem

Does your ABS light come on?
REar sensors I think are about £200 , each and front about £100 each , so thats a big labour bill?

Lego
Lego's picture
Offline
Joined: 13.09.2012
Location: Edinburgh
Re: ABS problem

Hi Jantie,

Ultimately my ABS ECU was faulty.  Myself and my garage tried most if not all of the suggestions in my original thread.
Luckily the garage i used had another G with the same ECU which they tried in mine and worked fine. Having just acquired another ECU I can confirm my ABS now works again.

Just to clarify:  What I did find out is - that the ABS system has a self test that occurs when the car goes over 5Mph forwards the first time after Ignition. If you have a fault with your ABS system the ABS warning light in the instrument panel will illuminate after failing the test, and you brakes will default to non-ABS standard brakes. The ABS  warning light and and non ABS brakes will stay that way until you switch off engine . The ECU has no memory so the next time you start up it will not show a fault until it does it's self-test.  I happen to have a very steep narrow driveway with a sharp turn, and my foot  needed to be on on the brake virtually right away after moving off. This coincided with the ABS self test at 5Mph. So I would get the pulsating and hard brake pedal with virtually no braking for a few scary moments during it's test,  before the Brakes would default to non-ABS and I would  then Skid a bit as i was pressing the pedal so hard. Then ABS warning light would come on.  So If  I wasn't pressing pedal during the ABS Self-Test I never got the pulsating, hard pedal problem, as the self test would fail and switch to non-ABS. 
At the time I had the added complication of there being no ABS warning bulb as somebody had previously removed it. 
I hope that makes sense and helps you in some way. :)

If you are not getting the ABS warning light coming on at around 5Mph and you get the pedal problem at higher speeds - I would hazard a guess that it's not the ECU. I would certainly have the ABS switched of permanently via the switch on dash.

If you have any other G wagon owner with same model/ecu nearby  you - you could ask if you could  try swapping it out to test. It would at least illiminate one possibility. Just make sure you put some identifying marks on it to avoid confusion.
.If ECU is the problem, then you have very little chance of finding anyone who can fix it.
 I tried lots of Companies. I did eventually find a second hand one(or rather Gav did) in Germany. It cost about £430 which is Very expensive but I have little choice as MOT due soon and not willing to go down the removing/ rewiring the bulb root to pass it.   Well Over 2k for ECU  from Mercedes I believe. You can actually remove the ECU as I did and still drive the car, as it just defaults to Standard non-ABS. So if you do happen to find somebody who can repair it you can send it off and still use the G.
If you do happen to have the same ECU as mine then I'm happy to test it in my G if you get stuck for testing.

fixwin38
fixwin38's picture
Offline
Joined: 09.07.2006
Location: northern ireland
GWOA Groups: Members
Re: ABS problem

Hi all
just experienced a similar bluff only in this instance somebody had pulled the instrument cluster and wired the alternator warning light circuit to the ABS warning light bulb so that the kight came on when you turned the ignition on and went out when you started the engine...with no ABS failure light coming on as you began to drive away ..no ABS working either
fault proved to be a grounded sensor cable to the rear r/h wheel

Pistonhead
Pistonhead's picture
Offline
Joined: 16.12.2006
Location: Loughborough
GWOA Groups: Committee, Members
Re: ABS problem

 Thank you fixwin38,

Interesting to know what some people get up to. I am not putting blame onto them, it is something that could happen to any one - experienced or not.