Why do you say that ECM diagnosis doesn’t exist anyway?
Because it doesn't..., at least not in the manner one would think it should for such a system. Stihl would have you believe the MDG unit is a diagnostic tool for troubleshooting and identifying problems with the M-tronic systems. It isn't. It's primary purpose is as an interface to the ECM for extracting, viewing, and printing limited data from the module (and in the future, possibly upgrading ECM's). It doesn't troubleshoot or diagnose performance issues aside from being an overly glorified and very expensive spark tester in lieu of shorting the plug to the cylinder and possibly trashing the ECM in the process. If it did what Stihl would have you believe it does, it could tell you whether or not you had a bad solenoid, which it can't. It could tell your altitude relative to the air/fuel ratio, which it can't -- even though Stihl claims the M-tron system adjusts for altitude. It adjusts for air/fuel relative to rpms and timing, (and perhaps case temperature), but hardly relative to sea level. No altimeters on these saws. No external sensors at all except a thermometer inside the ECM to sense and record general case surface temperature. Can't tell you if the carb is bad. Can't even tell you if the micro-switch is bad. Can tell you how many times it's been started and what the general conditions were, but that's about it for data.
Can walk a tech through the reset and cal process. But that's about it for the bell and whistle part. Basically doesn't tell you any more than the dealer will if you take your poorly or non-running M-tronic unit in for diagnosis..., even if he has the MDG system sitting right there on the counter.
"Well, it's either the carb, the solenoid, or the ECM..., or maybe the fuel filter. Have you tried a new plug?"
The M-tronic system is based on a very, very fast counter that monitors RPMs and timing to control a very, very fast switch that tells the solenoid what to do as an air/fuel mix valve on what is essentially a fixed jet carburetor. Period. It's all based on the desired performance algorithms programmed into the ECM firmware and how they respond to the physical changes of the saw as counted and processed. Sophisticated? Yes. Complicated? No.
All the above stated, (and generally understood simply from a certain degree of experience and research on the matter), I'm hardly an expert on the subject. And I'm pretty sure there's a guy with a test rig somewhere who
can literally watch the algorithms in action, look at a bunch of numbers, and tell whether or not an M-tron saw has a bad solenoid or was running lean for an extended period of time before the bottom end bearing failed. It's just not gonna be a guy at your local dealer, or probably anywhere else here in the states for that matter as I understand the majority of the M-tron research and development is happening in Germany... and on the Husky side in Sweden, of course.
Good fuel. Clean (and correct) fuel filters, a coupla spare solenoids..., life is good..., until the saw won't start. Diagnosis?
Try a new plug.
Nope no license required. You’re given a website to go to to download the required software on a card inside the kit. It includes the login info. It’s not that I don’t have a dealer that I have faith in. I have a couple that are useful in different ways. It’s more I’d rather not need one. I’m no different with my cars, generator, appliances, I’m sure you get it. I am at least as prepared to repair my saws (the new ones) as the folks employed to do it. And more so than a few. Anyway, it’s really all about learning and benefiting from it and trying to have some fun along the way. 
