OBDII monitors emission control components. If a component fails then the PCM could light the MIL or simply create an artificial value for it. It really all depends on its importance. A DTC will be stored regardless.

However, in your scenario you stated that a MIL would be illuminated if the MAF sensor read more airflow. That isn't correct. The MAF simply lets the PCM know how much air is entering the intake manifold and is a representation of engine load. If the MAF fails then a DTC is stored and the MIL is illuminated. But in your scenario you stated that you got the air/fuel mixture right so a MAF sensor reading more air isn't going to illuminate a MIL.

I'm going to school to get my associates in Auto Technology. I'm not currently working in the field so take what I have to say with a grain of salt. I am, however, finishing up my summer session of Emission Control Systems. I wish the OP would come back and tell us the fault codes his computer set so we could have a discussion of all the facts in this case.

They do every winter.

I was just reading something about how Minnesota is going to mandate that all diesel sold in their state is B-20. Does that mean that MB will have to change its position on Bio? Or is 20% not going to effect the newer engines?

They won't mandate it, it would be stupid of them to do so. They will have lawsuits out the wazoo from people with gelling problems and warranty repairs denied. Minnesota is about the last place that should be mandating any biodiesel because every Diesel would gel in their harsh winters. Texas, Florida or any of the southern states are the ones that should consider doing it.

Cummins is currently the only engine builder that allows more than B5 (B20).

It does seem silly for such a cold climate. Maybe things have changed since this was written;
http://domesticfuel.com/2008/05/12/minnesota-adopts-biggest-biodiesel-standard/

So you are wasting our time by not moving faster on your summer session? Hurry up, you are burning summer. :D It was something I read that told me that OBDII is more intrusive and doesn't only look at the functioning of the sensors but more in-depth into what the sensors are seeing and if it didn't fall into the correct parameters, activate the Mother In Law light. I too will have some checking to do.

Me too.

update on my GL 320 in limp mode
 

I thought I'd let you all know the outcome... as I suspected the emissions sensor was sensing that the emissions were out of whack (too low) since I was using biodiesel and have been using about a B80 blend for about 10,000 miles (with no problems). I drove it gently to avoid going into Limp Home Mode until I could make some room from regular diesel. At about a quarter of a tank down, I put in regular diesel and the "Check Engine" light went out after about 5 miles of driving the car. It's running great. (glad I didn't drain the tank!)

Biodiesel is nothing to fear and the diesel engine was made to run on peanut oil! It's not just about the emissions for me, it's about buying renewable fuel that is made in USA.

But thanks for your help and comments.

Yaaay glad to hear you are fine!
so yours has no issues with B80? that's nice. a customer of mine has a bluetec and was curious. I will parrot your experience to him!

Well technically it was invented to burn coal dust, but that's another story.

I'm glad to hear you made out OK. How many miles are on the GL? Did you start burning B80 since it was new? Are you going to continue burning a B80 blend if that keeps the light out? Please keep us updated as the miles pile up. I for one am glad you can burn more than a B5 blend.

I agree, that's why I use Biodiesel in all my [OLDER] Benzes. It would be financially safer in an older car, one that is no longer in warranty. However, it's your money. :D

Jeremy

Biodiesel is nothing to fear and the diesel engine was made to run on peanut oil! It's not just about the emissions for me, it's about buying renewable fuel that is made in USA.

But thanks for your help and comments.
Well technically it was invented to burn coal dust, but that's another story.

====================================
Rudolf Diesel originally tried to design an engine that would run on coal dust, because the Brits and the Americans had oil, but the Germans did not. A prototype of this original engine caused an explosion so loud that poor Rudy was deaf in one ear for the rest of his life.

George Washington Carver several years before had discovered many, many uses for penuts (curiously, though, peanut butter was not one of them), and since peanuts will grow in the Reich, Rudolph restated his objectives, probably not wishing to be entirely deaf.

Noe of this means that YOUR Benz was designed to run on peanut oil or coal dust, by the way. It perhaps SHOULD be able to do this, but should and can are different words.

.

Reminds me of our Govanators famous line....."I'll be back".

Around here it'd not even be an issue because I can only think of 3-4 stations in the entire area that sell any bio fuels....and all of them are far away....and it costs more....and there's risk with the new diesels. I'd be running dino just like I am currently. :D

Of course you can burn more than B5. The big question is for how long. There's no long-term scientific testing done on anything more than B20. Check out biodiesel.org. There's an article that talks about this. Even with warranty aside, blends higher than B20 should not be considered a drop-in fuel, especially on the new diesels with particulate filters where biodiesel may not be able to clean up the filter because it burns differently from diesel. But to the OP, it's your car & your money. All we can do is give advice.

That is flase information. Mercedes has never made any of their engines to run on biodiesel/wvo/svo.

That is false as well. If the emissions were too low it would not set a code.