Does the FSS monitor fluid quality? How does it work anyway?

There are a couple of different types of oil quality monitoring systems. The simplest type has algorithms built into the engine control system that uses mileage, the number of cold starts, average revs, and maybe average oil temperature to compute remaining oil life.

The most sophisticated type, which I believe includes the Mercedes FSS have a sensor that measures oil quality by monitoring the oil's dielectic strength. As the oil ages and becomes contaminated it becomes more conductive, so dielectric strength is a good measure of oil quality.

Duke

The FSS system on the M111 equipped cars does not have the oil "quality" sensor, but uses calcualtions based on driving conditions. The FSS system on M112 and M113 cars senses oil quality. Not sure about M119 or M104 cars. Did the R129 and W140 cars have FSS?

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John Shellenberg
1998 C230 "Black Betty" 240K

http://img31.exs.cx/img31/4050/tophat6.gif

I believe the capacitance of the oil is measured. I also thought that the M111 engines included this feature. If not, it wouldn't recognize an interim oil change or topping up with fresh oil.

Isn't there also some time limit such as 13 months between changes or am I incorrect on this assumption.

I always disliked this kind of feature on my BMW's. At least with Mercedes you can reset it w/o taking it to a dealer.

There isn't a 13 month limit - that's for sure. I've got a low mileage SLK230 and the FSS is pretty steady on the mileage count - looks like it ignores the time. That is why I would like to do an oil and filter change before it's due - too long between changes if I follow the FSS.

The engine types that are being mentioned - what type of engine does my car have? (Excuse my ignorance ... I'm a new owner)

The MB USA brochures for both the 2002 C-Class and the 2002 E-Class have exactly the same description for the FSS system...

'....The Flexible Service System in your Mercedes monitors the oil quality, engine loads, RPM, operating temperatures and driving habits to determine when regular maintenance is necessary.'

This covers not only the 3.2 liter V6 and 4.3 liter V8 but also the 2.4 and 2.3 Kompressor engines. They all have the same system.

The M-Class brochure says something similar but not in the same words.

The FSS system needs the ability to measure the quality of oil in order to identify if and when the oil is changed between resets of the FSS system.

I'd guess that if a vehicle has the FSS system, it has the Mercedes/Shell system to measure the capacitance of the oil, hence the quality of the oil.

None of these systems that I am aware of keep track of calendar time. For the Corvette there is a one year time limit regardless of what the oil monitor says, and it is up to the OWNER to keep track of the time interval if they want to keep their warranty in force.

Assuming Mercedes also has a time limit, as I expect they do, it will be in the owners/maintenance/warranty documentation that was delivered with the vehicle.

Reading this documentation can tell you a lot about your vehicle's maintenance requirements and how the various systems operate! A lot of questions posted here can be answered by simply reading the owners manual and other delivery documention.

Duke

Duke

I no longer have access to it but I don't remember the 2002 E-Class Owner's manual saying anything other than to do what the FSS system tells you to do. I don't think it described any technical details nor said to follow any time line.

One of the major concerns I have about buying a new Mercedes is this approach to maintenance. Mercedes have clearly implemented it because they want to keep the costs of so-called free maintenance to a minimum.

I much prefer the Lexus approach where they tell you to bring it in every 5K or 6 months, whichever comes first. Of course you pay for it but if you think about it, all you get from Mercedes is three oil changes, an air filter and one cabin filter. I believe Mercedes pay US dealers about $35 for an oil change so you see that all this free maintenance costs MB USA is about $200 or less.

BMW pays for all maintenance items. What that means is they pay for the same things MB pays for plus one set of front brake pads. Call it $300 in free maintenance. This is easily recouped by raising the price of the car.

Boy I could write all night about FSS. I could also find lots of training literature on it as well. Let me just respond to a few questions and slight mis-statements:

Yes, the last year or two of the 140, and last 4-5 years od the 129 had FSS.



If you know which 2 terminals to jump you can reset the BMW oil service or maintenance service lights, at least through the 80's and up into the 90's, not sure about current versions.

I believe "capacitance" is the term used in training. But I believe that the change in level is what makes the system recognize the addition of oil, not the change in quality, although it will notice the change in quality too. The sensor is both the level and quality senso, it does both jobs.

The 2.4 is also a M112 engine, not a M111 Kompressor motor, just to clarify this.

Yes, the FSS does keep track of time. The time can be programmed with the computer in the shop, I believe the setting from the factory is for 24 months. After the time setting has passed, you will see a small "clock" emblem (like an analog clock face) in the FSS display upon startup.

I agree with this, but only to a point; remember that FSS was introduced well before the Maintenance Commitment Plan was introduced. But it may have been a part of some "Evil Plan" for when it was introduced (being just slightly facetious here).

Gilly

Gilly,
Can the customer request a reprogramming of the system to shorten the time span between maintenance? I don't drive many miles anymore so it might be far too long between service calls with the default time frame.

If the system is reprogrammed to a shorter time frame, I assume that the minimum is something like 13 months. Mercedes isn't going to pop for more than about three free services

You can ask, sure. I mean, the shop "can" do it. Like usual, it always kind of boils down to "will" they do it. I am unsure how this would affect the Maintenance Commitment Plan. Maybe if the claim is submitted before MB thinks the work should have been done, then the claim may be rejected. What I mean here is that this Maintenance Commitment Plan is considered "warranty work" to the dealerships, it's submitted to MB just as a defective switch would be; MB pays for the work. It may be the best plan to go ahead and pay for the "off schedule" oil change only, then after the car is out of warranty change the time od the change back to 1 year. I'm sorry I don't recall how "small" the time element can be set to. I don't think it would be able to go to 13 months, I think it's done in like 3 or 6 month intervals.

Gilly

You know what? Now I seem to remember, when you look at the programming, that it was set in number of DAYS. Seems to me it was set at the factory on every one I've looked at, at 730 days, which is 2 years (OK, as long as there isn't a Leap Year in there )

Gilly

Last week I picked up my '00 S500 from the dealer after the "A" service and they forgot to reset the FSS and it still said the same mileage as when I brought it in until a day later when I reset it. This makes me wonder if it does measure the oil quality.

Randy
'94 E500
'00 S500

I remember seeing posts here from people who changed oil before the FSS system recommended it and the FSS system recognized the new/clean oil.

So maybe they didn't change my oil - I find that hard to believe but you never know! I think I'll go by and ask the service advisor what the answer is - maybe she'll paint herself into a corner!

Randy
'94 E500
'00 S500