You bring up some good points.
There is communication provided via the Data Link conductor to the dealership level scan tools like the DRBIII or possibly Star (JD Caples would be the one to know about the other than DRBIII possibilities.)
Isn't it true that after a number of failure to fire, the Espar locks itself out and needs to be reset with an MB star tool?
I've read that. From my research that may be the mode of a native Espar diesel fired heater. I've read that after so many start attempts the native Espar heater locks out and needs to be reset using the proprietary Espar access scan tool. OR maybe the permanent lockouts are related to specific component failures which are monitored by the Espar computer and people assume it has locked out related to a couple start attempts.
My Experience:
My 2004 heater main burner never fired for the first 6+ years that I owned my van. I tried it more than a few times over the years. Each time the most I would get was white smoke = unburned fuel. The Ignition Air Duct was plugged solid so the main burner never fired. When the button was pushed the red dash LED would light, the heater would try to start two times in succession and then would lock out, but not permanently. After an engine shutdown and restart it would again give two white smoke cycles.
After I cleaned the burner and screwed up the screen "wick" metering into the glow plug chamber I tried many more x2 white smoke cycles. There was never a permanent lockout. The heater runs fine now.
So, my experience shows that the Sprinterized Espar control module doesn't lock out for the (x2) failed ignition as described for the native Espar control.
My guess is that there is communication, just not visible through DAD?
And you very well may be correct. I'm going on the concept that the Espar module (computer) controls the burner completely as a stand alone unit. The Pin #6 & 7 "enables" are the only critical communication from the Sprinter.
If the Espar is communicating with the ECM or ATC via the Data Link conductor as you suggest then if I cut the wire that may stop my new happy association with my Booster Heater dead in its tracks.
I dunno, but I'm not that brave to chop it.
It may be an idiotic thing to do that and I'm just the idiot needed to give it a try. My ace-in-the-hole is that even without the DAD I can probably still get my buddy to connect the DRBIII to my Sprinter and reset things. I hate to bother him though.
Maybe I'll wait for warmer weather to try this.
Sorry to go on. vic