Hello all! I have a 2000 SL600 and the ABC suspension light came on the other day. I had the codes read with the STAR and these are the ones I got:

C1320 Damper valve FL Y51 (short circuit)
C1321 Damper valve FL Y51 (short circuit)
C1322 Damper valve FR Y52 (short circuit)
C1323 Damper valve FR Y52 (short circuit)
C1324 Damper valve RL Y53 (short circuit)
C1325 Damper valve RL Y53 (short circuit)


I followed the test steps recommended under Suspension Control (Automatic-Electronic): Testing and inspection 7.0-7.2, 8.0-8.2, 9.0-9.2, and got the correct voltage at the N51 connector and used a digital multimeter to check the ohms of all of the axle solenoid valves, and they are well within tolerance.

I have a hard time thinking that all three of these solenoids failed at the same time and at this time am thinking that the ABC module, or ABR module (part#018 545 95 32) is to blame.

Am I on track? Im hoping that someone with extensive knowledge with the STAR or this System can help? I have searched the forums in depth but have not found anything specific relating to my situation.

Thank you in advance!

Don't have specific info but can offer general information.

Did you check if the coils were shorted to ground rather than wire to wire?

Do you have access to a wiring diagram? There might be a common point that could drag the system down.

I'd also have a look in the suspension computers for water intrusion or an electrolytic capacitor leaking on the board.

Thanks for your reply 97 SL320. I did not check the coils for short to ground. Ill do that. I do have access to a wiring diagram and have been looking it over but have not found a common point. I did look inside the ADS N51 control module thinking I would find it full of oil or something similar to what I found in my 1999 E320 transmission control module, but it was perfectly clean and dry. It looks brand new inside. One thing to mention is that the wiring harness was slightly oily and i did notice a tiny drop of oil on a couple of the pins when i disconnected the module. This led me to disconnect the wiring from the damping valves and this is what I found on the drivers front.






So i am definitely going to replace that leaking damping valve, but the question is, could that valve have caused the fault codes for the RF and LR also? I am tempted to just replace that LF valve and see if the other codes resolve themselves. What do you think?

I'd change the leaking valve, clear codes and see what returns.

Oil is an insulator and shouldn't cause a electrical short, so the fault code cause is still unknown.

Ive got the LF damper valve ordered up along with all 4 of the air cells / cannonballs. Ill replace them, clear the codes and then see where we are. Ill post back once Ive done this with the result.

Well, I installed the replacement damping valve along with the cannonballs today. Refilled the system, cleared the codes and took her for a test drive. When I got back I shut off the car and when I restarted it, the ABC light was illuminated again!!! I read the codes again and the exact same codes were there. Another thing Ive noticed is that when I start the car, it slowly sinks down to the bottom of the suspension travel and then raises itself back to normal ride height. Once it does this it stays at the normal height while driving and while parked. When It is doing this, I can hear clicking coming from the damping valves. I can clear the codes, but they will return the moment the car is started. Has anybody had a problem similar to this that can shed some light on the situation?

At this point from the codes given I am guessing that there is a problem with either the wiring harness or the ABC computer/module. Does anybody have any advice???

thanks in advance...

I do recall that a failure in one can bring down all of them. I'd try systematicly disconnecting each in turn with a test drive for each one. When you return with only the fault for the disconnected one you've found the culprit.

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Thanks for the idea duxthe1. I did exactly as you described and unplugged the damping valves one by one and re scanned after each. No matter what valve is unplugged I still get the same codes listed at the start of this thread. Even though I just replaced the Left front damping valve with a new part directly from mercedes, I am still getting a code for it. What truly surprised me is that when I unplugged the one valve that isnt throwing a code, the Right rear, It didn't set a code.

Whatever my problem is, the damping valves being plugged in or unplugged doesn't seem to affect it at all. I still get the same codes, even after they are cleared. I can clear them and they stay cleared with the ignition in the acc position, but once the car is started, they are back instantly.

I dont know what else is left except the wiring harness and the ABC module itself. Unless another sensor could be contributing to this problem?

Does anybody know how I would go about testing the wiring harness or ABC module to determine which is bad? Id rather isolate the problem than throw parts at it. Do these modules have a history of going bad? How about the wiring harnesses for the ABC system on this year car?

I wonder if oil migrated in to the control module and is causing the errors. Trans controllers ( EGS ) act up when the trans connector leaks and oil wicks in to the module. Oil alone is non conductive, but perhaps there is enough fine metal in the system to cause a problem.

I know exactly what you are talking about 97 SL320. I had the same problem on my 98 E320's trans controller. Taking this into account one of the first things I checked was the inside of the ABC module and it was perfectly clean. This doesn't mean that the module is not at fault, Im actually thinking it is, but it has no oil inside and looks brand new.

Is there some way to test these modules without just throwing down $1400 and hoping it works?

At this point I'd check coil resistance at the controller plug as this will take into account wiring problems.

Using general electronic troubleshooting, use the pin out to find where the solenoids enter the controller and follow those pins down to the circuit board. See if there are any capacitors running from these pins, if these have failed and are shorted to ground it could cause the problems you have.

Thanks for the response 97 SL320.
As stated in the beginning of this thread :

"I followed the test steps recommended under Suspension Control (Automatic-Electronic): Testing and inspection 7.0-7.2, 8.0-8.2, 9.0-9.2, and got the correct voltage at the N51 connector and used a digital multimeter to check the ohms of all of the axle solenoid valves, and they are well within tolerance. "

I did check the resistance of the damping valve coils and all fell within spec. I didn't however check the resistance of any pins on the ABC/ADS Control unit because i could not find any diagnostic info for it.

I have attached a pic of the inside of the ADS control module. As you can see it looks very clean.. There are two linear capacitors on the board and neither appear to be leaking.

"" used a digital multimeter to check the ohms of all of the axle solenoid valves, ""

At the controller plug not each solenoid plug correct? Be sure to check resistance of coil to ground and coil to positive battery as well.

The gold / red stripe axial caps should be on the power side, the black disc marked ZNR is a surge absorber typically used to prevent incoming voltage spikes from damaging electronics further down stream. The caps across the solenoids / to ground I'm speaking of should be surface mount devices perhaps 3 mm long and 1 mm across.

I doubt they all failed at one time, there has to be some common point of failure. For the controller to know that a solenoid is shorted or open, it must measure current ( voltage drop across a low ohm resistor to infer amps ) There is a small chance it is measuring incoming voltage and comparing it to voltage going to the solenoids but, I'd think that would be to difficult to make work reliably.

Some systems I've worked on rely on the inductive kick induced when voltage to a coil is removed as a method to sense if the coil is there. ( think about how a ignition coil generates 30 KV from 12 VDC )

Did you take the back cover off and examine that side of the board?

Thank you to all that contributed to this thread.

I tested everything possible. All wires showed the correct continuity, voltage, and resistance.

I did take the back cover off of the ADS Module and there was nothing visibly wrong. No leaking capacitors, nothing.

Against the advice of others whom are not on this site, I replaced the ADS Module/computer. Reasons given not to replace were that the module hardly ever fails, If the module was bad, I would be getting a fault code for all 4 damping valves not just 3, etc.

Replacing the ADS module fixed the problem 100%. Once installed, the car leveled itself properly and it has thrown no codes. The ADS module was absolutely the problem.

Here is a picture of the back side of the bad ADS module just for reference or if anybody was curious.
[URL=http://s453.photobucket.com/user/bensjsjsj/media/photo-1.jpg.html]