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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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Discussion Starter · #1 ·
Hi All,
Firstly just to say great forum, I've used it on my occassions to help me with various problems, but at last I've decided to register!

OK, here's the strange ABS problem I'm having with my 1990 R129 300SL-24:

Turn the key, all lights come on as they should, start the engine all warning lights go out.
Press brake pedal, wiggle steering wheel no problem.
Drive off, and either one of two things happens:

1/ ABS/ASR come on more or less immediately as car starts to move

or

2/ On braking, ABS cuts in far too early on right hand side only, car dives to one side in process, then kicks back in opposite direction:eek: ABS/ASR warning lights illumunate and system turns itself off. From then on brakes work fine, just no ABS/ASR.

Obviously scenario #2 is quite dangerous! I first discovered this when braking hard on the motorway, and had a very near miss in the process as the car dived off to one side.:eek:

In any case, here's what I've done so far, all to no avail.

Replaced Right Front ABS sensor (New genuine MB Part), and cleaned pick-up ring.
Cleaned N/S ABS sensor and pick-up ring.
Left battery disconnected for a few hours.
Fitted a new 100ah battery.
Replaced OVP relay, and checked voltage accross (OK)
Checked voltage at ABS/ASR module (OK, as battery +/- 0.2v)

I also jacked up each wheel of the car and noted the following result:

Spin Right Front Wheel - ABS/ASR Lights Illuminate
Spin Left Front Wheel - OK, No Warning Lights
Spin Right Rear Wheel (ASR Switched off using button on dash) -ABS/ASR Lights illuminate
Spin Left Rear Wheel - (ASR Switch) - OK, No Warning Lamps

Also noted the ASR was working fine, when spinning the wheel with system enabled, I could feel the brakes being applied.

Then I took the car onto a quiet road. Reset lights by turning engine off then on. Drove with left side on gravel, right on dry tarmac - on braking wheel locked up, even though ABS/ASR lights were off.
Repeated with right wheels on gravel, left on tarmac and ABS cut in as soon as I touched the brakes, again no warning lights on.

So then, all wheels on dry Tarmac, sharp braking, car does its usual trick of ABS cutting in too early and diving off to one side before system switches its self off.

By the way, all the time I was doing this, they was an elederly gentleman walking his dog, who must have thought I'd gone mad driving back and forth, wheels in the gutter, jamming on the brakes:)

So, as you can imagine it's driving me to distraction..and I'm falling out of love with this beautiful car because of it.

Incidently, and it may be completely unrelated, but following the ABS/ASR lights coming on, the power hood stops working for 10-15 minutes, but come back ok after that. On reading the fault codes, it gives an Error Code 30, which is described as Hood Action Blocked?

As the problem seems to be with the right hand side, does this sound like a module issue, or could it be the pump itself? I've got to get this sorted soon, as the car is due it's annual MOT test, and will fail for sure with the brakes as they are.

Really hoping someone can help, as I'm fast running out of ideas here!:confused:

Mark.:)
 

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Administrator
1998 Pano SL500; 1993 SL500; 2005 ML270cdi
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9,054 Posts
Hello Mark and welcome, it does sound like control fault.

I've dug up the following which may be helpful

K6JRF Auto Page

http://www.benzworld.org/forums/r12...s-lights-still.html?highlight=abs#post2877253

http://www.benzworld.org/forums/r12...er-not-working-please-help.html?highlight=abs

You can also type in ABS into the search feature that will reveal a lot more info.
If you don't get anywhere you may have to bite on the bullet and go to a Mercedes workshop especially as this is a fairly serious safety issue.
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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30 Posts
Discussion Starter · #3 ·
Hi Redliner,
Many thanks for the info, much appreciated. Also done a few searches, the results of which suggest the soft top issue may actually be related.

I'm initially inclined to think it's the control unit, although if the lights go off on start up, and don't come back on again until the car moves, doesn't this suggest the module is OK, or is it that the module doesn't know what to do with the inputs once the car is in motion?:confused:
Also is there anyway to test the pump operation itself?

Thanks in advance,
Mark.
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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30 Posts
Discussion Starter · #4 ·
...just a quick update, soft top refusing to work again (stuck down, fortunately car garaged, so not a problem) Have flashed the fault codes off and got a Code 29 (No speed sensor signal) and a Code 30 (Soft Top Operation Blocked)

Questions are:
1/ Could the speed sensor be directly related to the ABS issue?

2/Where is the sensor located that the soft top system takes it's signal from?

Mark.
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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30 Posts
Discussion Starter · #5 ·
...sorry to keep adding to this, I feel I'm making this my own personal thread!

I did some searching on the forum and found member DR500 had exactly the same problem as I have with his 1991 500SL, although his ABS/ASR was completely shutting off. I pm'd him to see if he'd found a solution.

He said he'd replaced the speed sensor in the diff housing and it cured both the hood mechanism and ABS/ASR issue. However, I've read that the hood system takes its signal from the left front ABS sensor...is this correct?

Mark.
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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30 Posts
Discussion Starter · #6 ·
Possible solution!

Hi Guys,
It seems I'm the only one posting on my thread :(, but in the name of helping others in the future I'll continue to post up my progress and findings, I certainly owe it to this forum, who's topics have helped me in the past.:thumbsup:

Well, I think I may have cracked this after an evening in the garage with a multimeter!:D

It seems the cause may be two fold. There's a break in the loom from the Left Front ABS sensor to the connector in the relay box at the left side of the car, which if you wiggle around sometimes makes a connection. Also the ABS sensor, although providing a pulse, isn't as good as it should be...resistance across it is 1010 Ohmes, whereas the new Right Front Sensor is giving a reading of 1610 Ohmes, both at the sensor itself and at the connector on the Right side of the bulkhead, near the heater duo valve.

With regards to soft top operation, as soon as the codes are cleared it works again, until a road wheel is turned, then a code 29 is logged.

Will track down a new loom and sensor and post the results once fitted. Fingers crossed, it should cure the problem.

By the way the speed sensor in the diff housing I mentioned in a previous post, is, as far as I'm aware, solely for the speedometer on the 300SL-24.

Mark.
 

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Administrator
1998 Pano SL500; 1993 SL500; 2005 ML270cdi
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Mark, thanks for the ongoing posts which are very informative and useful.

Please keep posting in with news of your progress.

The soft top problem which you relate to the wheel sensor is also very interesting.
I'm sure when Bob comes across this topic he will be able to advise :thumbsup:
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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30 Posts
Discussion Starter · #8 ·
.....just an update

Fitted a new L/H/F ABS sensor, still no change:(, although noted resistance across new sensor was 1610 Ohmes, considerably more than the old one (app 1010 Ohmes), but the same as the new R/H/F sensor, so it's a fair assumption that they were both on their way out anyway (which makes me feel better about the GBP180 I've spent on them!)

So, removed the lead that connects the ABS Sensor & Brake Pad wear indicator to the main loom yesterday (what a job) It runs down the strut, through bulkhead (firewall) into the relay box, but is routed under the bracket that holds all the ECU's, so most of them have to come out and you have to raise the bracket which still has about 100 wires attached to it, then MB, being MB, have used 5 cable ties within a foot!.

Well worth it though, got it out and located the culprit wire - in the red wire, all the copper strands had oxidised and gone black and brittle and was only sometimes making a weak connection. I think water had got into a crack in the outer insulation, caused by years of susupension & steering movements. A gentle tug on the offending wire and it just broke in my hands. New lead now waiting for me at local MB Dealer...GBP 97 + Vat, day light robbery for a piece of wire 4 foot long with four connectors on it....if it works though, it'll be worth it!

Will post the results..please, please let this be it !! :bowdown:

Mark.
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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Discussion Starter · #9 ·
Result!

......well guys that was it! fitted the lead this afternoon, put everything back together. Drove off down the road holding my breath and hey ho!, no ABS/ASR lights.:D
Found a patch of gravel on a quiet road and jammed on the brakes...text book ABS operation on both sides of car. Then planted rear wheels in the gravel, hard on gas; text book ASR operation.

Lesson from this exercise;

  • Don't automatically condemn big stuff like control units and pumps when you get a problem like this. They're very durable units and don't often go wrong. Take your time, keep an open mind and don't jump to conclusions.
  • When you buy the car make sure the the ABS/ASR lights come on and go and stay off. The last owner of my car had removed the bulbs in the ABS/ASR lights to hide this problem. This is my own fault for not checking thoroughly enough when I bought it....and I should know better being in the motor trade!:eek:

I've kind of made this thread a diary of my experience. I'll consign it to the archives now, so hopefully someone else will benefit from my trials and tribulations.

Mark.
 

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1998 Pano SL500; 1993 SL500; 2005 ML270cdi
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Many thanks for the write up Mark, and congratulations that you have found the fault.
As you rightly point out, it's not always the big expensive components that are the problem and quite often a much cheaper associated component or bad electrical contacts.
 

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2007 CLS 550, 1998 Harley Road King, 2011 F-150 EcoBoost, '65 Shelby Cobra
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978 Posts
Mark,
Congrats on the ABS/ASR solution. Good detectived work. I did not see how it all fit with your not responsive top, however. Did your fix correct it as well? As you know, if you are trying to operate the top and it senses any movement by the car, it will stop working as a safety factor. Searching this forum on soft top problems will yield enough reading material for a lifetime. :eek: I hope all is well.
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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Discussion Starter · #12 · (Edited)
Mark,
Congrats on the ABS/ASR solution. Good detectived work. I did not see how it all fit with your not responsive top, however. Did your fix correct it as well? As you know, if you are trying to operate the top and it senses any movement by the car, it will stop working as a safety factor. Searching this forum on soft top problems will yield enough reading material for a lifetime. :eek: I hope all is well.
Hi Mike,
The soft top mechanism takes it's "speed" signal from the Left Front ABS Sensor. It's a safety features, so if the car is moving you can't operate the soft top (for obvious reasons:eek:)
For this reason, if the soft top mech mechanism can't detect a signal from the sensor, as a safety measure, it shuts the mechanism down and hence the mechanism stops working. A fault code 29 (no signal from speed sensor) and a fault code 30 (soft top operation blocked) are then logged in the roof control unit.

I forgot to mention that when I'd refitted the new ABS/Brake Wear Indicator connection lead, reassembled everything I'd removed and re-connected the battery, I had to first read and clear the soft top fault codes stored in the control unit. Even though the battery had been disconnected for a day or so, while the car was in my garage, and I was working on it, the codes were still there. (must use a kind of EPROM system)

By the way I know what you mean about all the info that comes up when you do a search on the soft top mechanism; I spent until 2.30am one evening dredging through hundreds of threads. It's just a case of picking through it all to find what was relevant to your problem.

Mark.:)
 

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Administrator
1998 Pano SL500; 1993 SL500; 2005 ML270cdi
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By the way I know what you mean about all the info that comes up when you do a search on the soft top mechanism; I spent until 2.30am one evening dredging through hundreds of threads. It's just a case of picking through it all to find what was relevant to your problem.

Mark.:)
We are starting work on painstakingly going through the two convertible top threads and posts to make it a lot easier to get to information on the most common problems concerning the electrical, hydraulic and mechanical issues.
It won't be a quick fix so in the meantime please be patient and refer to the two existing convertible top stickys.
 

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Hey, good writeup!

I have a similar problem with my 1998 C-class.
BAS/ABS & ASR lights stay on occasionally.
When I've driven for a while, shut down the car and restart, the lights go off.

This makes me think it is kinda the same problem as yours, being that there's a crack in the sensor insulation which shorts out when wet, and after been driven for a while it dries up so upon a restart the lights go off.

I hit a cat someday which teared off some plastic molding under the car where I can see some modules with wires going in which don't look waterproof to me. I suppose I can order this piece of plastic at my local stealership or is there another way?

A question about measuring sensors, are U sure U can measure a sensor by resistance? How do the sensor's work exactly?

Cheers :thumbsup:
 

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'90 R129 300SL-24, 94 C140 CL500, '92 W140 400SE,'98 W210 E300TD
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30 Posts
Discussion Starter · #15 ·
Hey, good writeup!

I have a similar problem with my 1998 C-class.
BAS/ABS & ASR lights stay on occasionally.
When I've driven for a while, shut down the car and restart, the lights go off.

This makes me think it is kinda the same problem as yours, being that there's a crack in the sensor insulation which shorts out when wet, and after been driven for a while it dries up so upon a restart the lights go off.

I hit a cat someday which teared off some plastic molding under the car where I can see some modules with wires going in which don't look waterproof to me. I suppose I can order this piece of plastic at my local stealership or is there another way?

A question about measuring sensors, are U sure U can measure a sensor by resistance? How do the sensor's work exactly?

Cheers :thumbsup:
Hi Jomzo,

..poor pussy cat:crybaby2: did it make it:crybaby2:

As far as I know the sensor are magnetic coils, which when metal object passes through the field, generates an electrical pulse. I measured the resistance between the two wires that come out of the sensor at 1601 Ohmes (on my multimeter's 20K scale) The old ones which I removed were only showing 1010 Ohmes.

If you then track the wire back from the sensor, it will be connected to loom. If you disconnect here, you'll be able test for continuity in the wire. Zero resistance wire ok, open circuit wire broken - simple as that. Obviously you have to disconnect at the ABS sensor end too.

Alternatively, as a short cut, you can just disconnect the wire at the loom and directly test the resistance of the ABS sensor from there, which will give you a good initial idea if there's a problem.

Hope this helps.

Mark.:)
 

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W124 300CE-24 3.4 AMG, W186 300b, W112 300SE cabriolet
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Another strange roof/ABS issue

Hello from Australia, I normally hang out on the ozbenz.net forum, but have an interesting problem with a 1994 SL500 which has brought me here via a Google search. Much like merc-mark my problem effects the ABS/AST system as well as the soft top.

The ABS and ASD lights are on all the time and the roof will not operate. I have a HHT from a MB dealer that went bust so can read most stuff. Checked all the obvious stuff like the wheel speed sensors and they are all reading (speed) to within 10% of each other. Then had a look at the "actual values" using the HHT and find that no mater what the car is doing the ABS module is telling the RV (roof) module that the car is stationary!!

If I clear the code the roof work until I drive the car, move it even a few meters (yards) and the fault returns. I suspect the ABS module, but figured before i go pullingthe car apart I should check to see it anyone else has been down this road before.

Any help much appreciated.
 
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