Removing the Evil Spirits from the Mercedes
I woke up early this morning (6am) and drove the ML down to Utah Valley for a 7:30am service appointment at the Mercedes dealership in Lindon, Utah. The dealership is brand new (I was told it had only opened eight months ago) and is situated in a nice location, right in the center of Utah Valley (by the Home Depot at the bend in I-15 near north Orem). I only wish it was around back when we lived in Provo. At the time, the only Mercedes dealership in Utah was the Ken Garff outfit in SLC (our experience with Ken Garff was not good). This new outfit is run by Larry H. Miller.

I checked the car in with the service desk and explained, to the best of my ability, the short history of the problem we were having and the previous attempts made to fix it. I then turned over the keys, settled down in one of the cubicles provided for the customers, connected to the free wireless access point made available, and started doing some work. After about half an hour, the tech working on my car (Dan?) came out to summarize his findings and to ask me for some additional information.

Now, I should state that in all my days of taking the Mercedes in for either scheduled or unscheduled service at any of the many dealerships I have patronized (from LA to SLC to Boise to Bellevue), I have never interfaced directly with the tech working on my car. Never. Instead, I have always got the info from the tech indirectly through the service manager. And though the service manager was present in Lindon (and I did have many conversations with him throughout the morning), the tech either made a decision to talk to me personally, or the service manager gave him permission to talk to me personally. In any event, it was highly unusual; and I must admit, it was highly refreshing.

After exchanging greetings, Dan explained that he had pulled the codes generated by the recently illuminated check engine light and invited me back into the work area to discuss. I enthusiastically accepted. Dan walked me over to a touch-screen monitor and a computer (both mounted on a portable cart) that he had connected to the ML's on-board diagnostics. He explained that the check engine light was tripped by a (supposedly) faultly Mass Air Meter, i.e. the same thing that the Boise dealership had noticed (and replaced) during our trip from SLC to Seattle last month. I had noted in the service report that I had just replaced the Mass Air Meter one month prior, so I guess that upon reviewing this, Dan figured he needed some additional information so he could determine what may be the true source of the ML's troubles.

It is truly remarkable how much information is logged to the ML's on-board diagnostic system. After showing me much of the data that he had downloaded (so he could rule out each system, e.g. a problem in the transmission, etc.), he explained that problems with the fuel filter sometimes will get logged erroneously as problems with the mass air meter. Or in other words, he theorized that the engine lurched under extreme loads because it either, 1) wasn't getting enough air, or 2) wasn't getting enough fuel. His hunch was that the on-board diagnostics was assuming by default a problem with the air flow, because of the absence of the ability to monitor the volume of gas getting through the (presumably) partially clogged fuel filter. Thus it was logging the faulty Mass Air Meter codes.

The fuel filter was supposed to have been replaced at 60,000 miles; Dan observed that it had not been replaced (and I can't recall if it was replaced, but I'll have to confirm that with my records back at home). Furthermore, apparently Mercedes Benz had re-engineered the fuel filter back in 2000 (our ML is a 1999 model) and recommended to customers that it be used when older fuel filters are replaced. Dan explained all of this in great detail, helpfully pointing out where the fuel filter is located on the ML (it isn't in the engine compartment like I presumed, but back by the fuel tank underneath the rear seats). Dan also showed me what the old-style fuel filter component looks like and what the new one looks like. Dan also asked me if the fuel status indicator ever registered more than ¾ full... I responded that yes, even after I fill up the ML, it never shows more than ¾ full (this has always been to Kristy's great consternation). Dan explained that the fuel level indicator is part of the entire filter component, and that this element of the component was also upgraded.

So, I shrugged at the recommendation (what else could I do?). Change the fuel filter... why not? We have already taken several stabs at addressing the problem, maybe this will finally be the equivalent of shaking some holy water on the thing and ridding it of its evil spirits. I green-lighted the repair order and waited a couple hours for the repair to be complete (to the tune of some $700). Dan showed me the dirty filter after he removed it - it looked, well, it looked dirty, but not overwhelmingly so.

Even if the cause of the problem doesn't turn out to be the fuel filter, I must state the service I received at the Mercedes dealership in Lindon was nothing short of stellar. Props to Dan for giving me such a high level of personal service.

I'll report back if we experience any further problems.

(Update: Sun Sep 11 10:07:34 PDT 2005 // made it back home without any problems)
(Update: Mon Sep 12 15:53:07 PDT 2005 // confirmed fuel filter was not replaced at 60k)