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Discussion Starter #1
Ok, where to begin. Well I owned a 1991 500SL since 2007 now. The cars ADS was deactivated by a previous owner. After 12 long years I finally restored the system back in the car. It wasn't cheap nor easy, and I've yet to enjoy it as it has a MIL ADS dash light on

I bought a lot of components new, such as shocks, springs, spheres, all the main hoses that run from the pump to the tank to each individual shock absorber. I bought some items second hand from scrap yards such as front and rear valves and some hydraulic lines.

Upon installation, the dash light came on and it gave me DTC 5 Steering angle sensor. There was no angle sensor on my car as my steering wheel was updated to the 96-98 AMG model. I looked up several topics here and used ilcats.ru to get the correct part numbers and hunted for cars with ADS on the scrap yard. After installing humorous Steering Angle Sensors, I always get the DTC 14 Steering Angle Not Activated/initialized. I tried full left lock full right lock and nothing happens at all. The steering angle part number I got was 0085429517 it was from a 91 500SL with ADS, I even got the horn contact plate from the same car, still nothing.

After various attempts, I decided to try the 96-02 steering angle sensor, part number 0005426418. I had to change the steering angle sensor black plug/bracket and airbag plug/bracket to fit my car. I used the ones from the other period correct SAS. Did a full lock left and right turns and viola!!! It works, the light went off. Or so I thought.

Well the light did go off but only for like 10 seconds, it came back one and now it stays on permanently, as in it's on as soon as I turn on the ignition. The DTC is 4 though, which is wheel acceleration sensor. I can't seem to be able to delete this code, it is permanently on. I bought two sensors from the scrap yard for dirt cheap but they didn't work. One of them managed to kill the MIL light for like 5 seconds but it came back on.

Now I'm stuck looking for wheel acceleration sensors in the scrap yard. They all seem in such crap shape, new ones are like 800$. Did anyone have a similar situation like this, or did anyone attempt to fix one of these sensors. I know they are very sensitive to shock it seems

Sorry for the long post, I hope the forum doesn't format it without paragraphs as I noticed that this tends to happen when posting on my phone.
 

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Code 4 does not indicate a faulty wheel acceleration sensor per se. Wiring and the ADS controller could also be at fault, and that's what I would look at. Refer to the diagnostic manual for guidance: STAR TekInfo.
 

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Discussion Starter #3
Thanks for the link Bobterry, I tested the connection using a voltmeter of the ABS harness where the wheel acceleration sensor connects and also from the harness to the N51 module. It seemed fine

I also swapped in a used ADS module in place of N51 and the light did go out but only for a few seconds. It came back on and gave me the same DTC 4 reading. I tried switching back and forth between my original N51 module and the spare one but nothing happened, the light stay on no matter what.

So i returned the module and kept mine, thinking it's probably the wheel acceleration sensor.
 

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Discussion Starter #4
Code 4 does not indicate a faulty wheel acceleration sensor per se. Wiring and the ADS controller could also be at fault, and that's what I would look at. Refer to the diagnostic manual for guidance: STAR TekInfo.
Bobterry I went to the scrap yard today and tried two different ADS computer modules N51. Upon plugging them in I still have the ADS dash MIL light, but now it's giving me DTC 13 Oil Level switch instead of DTC 4 wheel acceleration sensor! Both of them.

When I switch my own ADS module back in it gives me DTC 4 wheel acceleration sensor. Does that mean my module is bad? Also please note I tried another module previously that managed to kill the light for a few seconds the first time but came back on with DTC 4 wheel acceleration sensor.

The weird thing about these codes is that they are not erasable and that while reading them they give you no other errors whatsoever. The same thing happened with the steering angle sensor, however when I was trying sensors, the car would start for a couple of seconds with the MIL light out and then come on. And there were no other codes than the steering angle sensor back then as well. The wheel acceleration sensor started to give me an error only when I installed the 96+ SAS which cleared that fault.

It's weird that you have to fix each fault to see the next one, that doesn't make sense. Specially that when my rear dampening actuators were disconnected I was able to read them normally and along with other codes and fix them respectively.

What do you think? Is it an ADS N51 module or wheel acceleration sensor or oil level switch?

Appreciate your help
 

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There was a reason the previous owner decided to kill the ADS on this car! Ask to all the M120 owners how many headaches they had trying to fix their stock ADS...
 

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Discussion Starter #6
There was a reason the previous owner decided to kill the ADS on this car! Ask to all the M120 owners how many headaches they had trying to fix their stock ADS...
Not really, the previous owner was a cheap bastard who rather delete anything or take shortcuts than fix it properly. Anyways that's besides the point.

I just need to pin this electrical fault down to one thing and fix it up.
 

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Is it an ADS N51 module or wheel acceleration sensor or oil level switch?
The odds say your N51 is bad, but you can eliminate the uncertainty by checking the oil level sensor with a basic multimeter. See the diagnostic manual instructions for troubleshooting code "13". (If the sensor is bad the resistance across it measured at its connector or the N51 connector is less than 500 ohms).
 

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Discussion Starter #8
Is it an ADS N51 module or wheel acceleration sensor or oil level switch?
The odds say your N51 is bad, but you can eliminate the uncertainty by checking the oil level sensor with a basic multimeter. See the diagnostic manual instructions for troubleshooting code "13". (If the sensor is bad the resistance across it measured at its connector or the N51 connector is less than 500 ohms).
Here's an update.

I switched the N51 module with the one that was giving me DTC 13 oil level switch. I check the wires of the oil level switch and they were brittle, upon cutting and placing new plugs on the wires I was able to delete the DTC 13.

Switched on the car and the light went out for a few seconds but came back on. I read the codes again, it gave me DTC 14 steering angle sensor not initialized/activated. I did the full lock left and right multiple times and it gave me DTC 5 Steering angle sensor instead.

I noticed that if you disconnected the SAS it will still give you DTC 5. So DTC 5 is the N51 module not reading the SAS at all. The SAS installed on my car is the 96+ model year version which shouldn't work on my ADS I car. I'm thinking of trying the 91 SAS versions that I tried before, maybe it would initialize with the new N51 module. With the old module all the old version SAS were giving me DTC 14 SAS not activated, and weren't resetting with the full lock method.

Maybe it would work this time with the different N51 module.

Bobterry, the new 96+ steering angle sensor part number 0005426418 shouldn't work on my 91 model year right?
 

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My guess is that the later steering angle sensor will work with your car.

I would test. Unplug the electrical connector to the ADS controller and with the key on measure the voltage between its connector sockets #21 and #23. Measure both AC and DC voltage and report back with a description of what you measured.

If the sockets aren't numbered and the identity of the above sockets as ambiguous, then know that #21 is wired to a green wire and #23 to a brown wire.
 

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Discussion Starter #10
My guess is that the later steering angle sensor will work with your car.

I would test. Unplug the electrical connector to the ADS controller and with the key on measure the voltage between its connector sockets #21 and #23. Measure both AC and DC voltage and report back with a description of what you measured.

If the sockets aren't numbered and the identity of the above sockets as ambiguous, then know that #21 is wired to a green wire and #23 to a brown wire.
Hey Bobterry, sorry I took some time as I didn't have access to a multimeter, got one now.

I measured ad you said between pins 21 and 23 in the ADS module connector, I got the following

DCV = 7.28
ACV = 5.28

Does that sound right so far?
 

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I measured ad you said between pins 21 and 23 in the ADS module connector, I got the following

DCV = 7.28
ACV = 5.28

Does that sound right so far?
Those measurements seem plausible to me. I'd take a measurement on my car and compare, but I don't have a multimeter at the moment. If you send a PM to Pazo, maybe he'll check his car.
 

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Discussion Starter #12
I measured ad you said between pins 21 and 23 in the ADS module connector, I got the following

DCV = 7.28
ACV = 5.28

Does that sound right so far?
Those measurements seem plausible to me. I'd take a measurement on my car and compare, but I don't have a multimeter at the moment. If you send a PM to Pazo, maybe he'll check his car.
Ok sounds good, I'll try to reinstall the old style SAS in the next couple of days and report back my findings here
 

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Discussion Starter #13
Ok got a new update.

So I changed the ADS N51 module and went back to use the older style SAS. I noticed that both the airbag and the horn were offline as well with the old style SAS. I figure that's because of the rewiring that we had to do to fit the new style SAS and 97 AMG steering wheel with the horn buttons.

After rewiring and using the old style combination switch with the two brass/copper contacts. We found out that the horn contact plate was sitting too deep in the steering wheel, so we used some 2mm screw washers and stacked them to make the contact ring sit further out in the steering wheel.

Assemble and the ADS light went away after full lock left and right, the horn works and the SRS light went away as well.

However, this doesn't have a happy ending. The light did stay off, but the switch to raise and lower the car lights up when pressed but the car doesn't respond. I know the car raises and lowers when you operate the lever underneath the car on the front and rear ends respectively. So that means it must be the part that attaches to the main ADS distributor and has a solenoid and connectors. When I press the button to raise or lower, I don't hear any clicks from that area.

I remember Pazo and GUSMB writing a post about this very same issue and taking apart that distributor and cleaning a clogged small filter and some other parts. I will try to follow in their steps and see what happens.

One more thing, with the ADS MIl off, I thought I would finally try that "magic carpet ride" as described by most members here. However, it doesn't feel very different than before. Probably not as stiff but not as comfortable as I thought it would be. If I was driving blind, I would swear it was a regular suspension car. Then again, maybe because it is malfunctioning and doesn't raise or lower by switch or at speed, so the ride is compromised?

And how big of a difference is the sport/comfort switch? Sometimes I notice it, but sometimes I feel it's placebo effect, but I only had half a day to try it out and perhaps didn't push it as hard as it could go.

Anyone with ADS cars feel free to chime in.

Sorry for the super long post
 

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From what I've gathered after reading many, many posts, I would start with checking all of the suspect wiring harnesses. You've already indicated the oil level wire was bad. I would check all the harness for insulation failure first. I'm about ready to acquire a 95 SL600 and that will be my first project, rewiring the harnesses.
 

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From what I've gathered after reading many, many posts, I would start with checking all of the suspect wiring harnesses. You've already indicated the oil level wire was bad. I would check all the harness for insulation failure first. I'm about ready to acquire a 95 SL600 and that will be my first project, rewiring the harnesses.
Hello Spud06

My car is a 91MY with CIS KE-Jetronic fuel injection, so it is exempt from the wire harness issue that affected the 93-95 LH fuel injection cars. The wire of the oil level switch I mentioned was a bit brittle yes but just the end connecting to the oil level sender, due to age and extreme heat here.

I'm suspecting the ride height solenoid that Pazo mentioned in his post and I pm'd him as well regarding that. I didn't have free time yet to tackle this issue, but most probably I will in the next week or so.

Now everything works fine with the exception of the ride height switch. After some high speed testing ;) I can confirm that the sport/comfort button works. The car has way less body roll when sport mode is activated, and is a bit forgiving when comfort is selected.

The only thing that is a tiny bit disappointing is the level of comfort with ADS isn't what people claim or made it up to be. Then again, I probably had very high expectations. I've been watching a lot of those old Citroen videos to get a better understanding of how the system works, but most probably the Citroen older cars have a much different iteration of the system that is geared more towards comfort. Some of those cars can drive on three wheels :)

I'm quite happy with the sport side of it but the comfort side isn't as comfortable as my 1996 E320 W210. That car has 16 inch tires though and I have the staggered 18 inch AMG setup. So that probably explains it.
 

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Ok so here's an update.

My ADS works but not the button to raise or lower the car. The sport comfort button works and I have no dash lights at all. I read Pazo's thread and tried installing three different solenoids that control this function, One of them raised the car a tiny bit and then stopped as fluid rushed out of the hex screw as it wasn't properly tightened. We re-bled the system properly but it still doesn't work.

I test the solenoid with a car battery and it gives an audible click when 12volts are applied. You can also feel that click if you put your hand on the solenoid while installed in the car and have someone press the raising button.

I removed the sintered filter completely but still nothing, bled the car and tried again but still nothing.

Now I know that the car works perfectly and raised when you raise the lever by hand, I also know that the solenoid gives an audible click when you press the button or test it with a battery. That means the car is getting the electrical signal to raise, but it not sending enough oil pressure into the front and rear pistons that are attached to the levers. We are able to move the piston earlier but not it seems much tighter.

Does my problem lie within the solenoid or the pistons that should push up on the levers or something else entirely?
 

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AG129, glad to hear your ADS works now.

ADS1 height control is a simple system, where majority of problems is related to dirt or leaks.
- You write that you have verified the two-way solenoid; it clicks when height change is selected.
- You also mention you have removed the tiny sintered filter from your main valve (Y36).
- Your control rod pistons could be jammed but unlikely both have failed simultaneously. Rods can be checked by looking at them when an assistant operates the height control switch – they’d change length immediately.

So the remaining issue I can think of is jammed check valve in the main control valve. There are three check valves that the sliding piston actuates. The suspect one is behind the scrub screw in oil channel ”S”. When the car runs, also this check valve opens and delivers pressure to Y36 height control from front spheres. I managed to clean this valve by accessing from both sides with thin steel wires plus compressed air. AFAIK this check valve cannot be dismantled. This is only my best guess since you write ”not sending enough oil pressure into the front and rear pistons that are attached to the levers”.
There are a few relevant pictures in this (somewhat exhaustive) thread: https://www.benzworld.org/forums/r129-sl-class/1324023-adaptive-damping-system-ads-hydraulic-suspension-3.html

Good luck!
 

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Discussion Starter #18
AG129, glad to hear your ADS works now.

ADS1 height control is a simple system, where majority of problems is related to dirt or leaks.
- You write that you have verified the two-way solenoid; it clicks when height change is selected.
- You also mention you have removed the tiny sintered filter from your main valve (Y36).
- Your control rod pistons could be jammed but unlikely both have failed simultaneously. Rods can be checked by looking at them when an assistant operates the height control switch – they’d change length immediately.

So the remaining issue I can think of is jammed check valve in the main control valve. There are three check valves that the sliding piston actuates. The suspect one is behind the scrub screw in oil channel ”S”. When the car runs, also this check valve opens and delivers pressure to Y36 height control from front spheres. I managed to clean this valve by accessing from both sides with thin steel wires plus compressed air. AFAIK this check valve cannot be dismantled. This is only my best guess since you write ”not sending enough oil pressure into the front and rear pistons that are attached to the levers”.
There are a few relevant pictures in this (somewhat exhaustive) thread: https://www.benzworld.org/forums/r129-sl-class/1324023-adaptive-damping-system-ads-hydraulic-suspension-3.html

Good luck!
Hey Pazo

I looked at the thread but couldn't identify the check valve you are talking about. I took a screenshot and circled round the S oil channel. Is this it or do you mean the S channel in the main valve/distributor where all the hydraulic lines are connected?

How do I check that it opens when the car runs? Don you mean to disconnect the oil line at S in the main distributor? I believe the main distributor feeds two lines to the front height valve and two lines to the rear one.
 

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The ADS system is engineered more for highway use rather than the old Citroen setup which seemed designed to traverse a plowed field. I think I even remember seeing a video of an old DS that was still mobile after removing 1 wheel. The ADS option doesn't offer those capabilities.

For an inkling into what ADS can do, read either the ADS I or ADS II information/maintenance (I only know about the ADS II system).

https://arkiv.mbentusiastklubb.no/teknisk data/129/annet/r129-ads-ii.pdf

Having owned an ADS II equipped R129 for a few years, I can say there is a noticeable difference between the hard fault ride, the Comfort setting and Sport. I've experienced all these situations. I can also say that tire selection does play a part as well. I've never experienced the ride with the 16 inch tires, but the Continental ExtremeContact tires on the 18 inch AMG Aero II rims was pretty good. My current General Tire equipped wheels are a little noisier and harsher, but the price was right and they are lasting WAY longer while offering better handling.

I can't help but think that the original 16 inch rims would provide the most luxurious ADS ride due to the volume of captured air per tire. The 18 inch rims are adequate for comfort, but most likely not ideal. I find the greatest use of the ADS system for highway travel. If the road is in good condition, the Sport setting provides a tighter chassis, but when the road surface degrades or has expansion joints, a flick of the ADS rocker to Comfort does a nice job in muting a jarring ride.

The R129 is a GT and ADS makes it a more enjoyable tourer.
 

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Well AG129,

Opposite to your upper encircled "S" is a grub screw with 3 mm allen head. In this channel there is one of the three check-valves the sliding valve actuates. This specific S-channel valve provides oil pressure for the height control rods, front & rear. My hypothesis is that you could have dirt/sludge in this valve. It cannot be disassembled but you can try move the check-valve by pressing with thin wire from both sides until the valve moves freely, maybe 1-2 mm. Sorry to say, to do this you must disassemble your ADS1 main control valve.

See also Jon Bearpark's drawing in this thread. Also, see this picture.

Hope I managed to clarify…?
 
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