Son's NA coupe transmission went into limp mode a couple times last week, so I ordered a connector plate kit from Mercedessource (enjoy his Youtube output). Knowing that I had to reset the TCM, I was vacillating between iCarSoft i980 (had a review that mentioned Crossfire) and Autel Diaglink (only one generic Mercedes review).
Padgett convinced me, unit arrived yesterday. Per the Amazon listing, downloaded the Maxi PC Suite 1.21, plugged in the DiagLink via USB and set it to update mode, then the Suite let me update the generic OBD software and pick a free manufacturer software module (the oddly-titled Mercedes oil reset one works for us).
Wow. Once I connected to the car, turned ignition on, and drilled down manually to R170 SLK320, I saw loads of fault codes that had accumulated over the car's 193k miles but had been intermittent or not lit the MIL. I had reset codes before with my cheapo $20 OBD reader, but clearly it hadn't reached into the MB modules very deeply.
After clearing all the codes and taking a short drive, the only code was for left rear wheel speed sensor open circuit. I set the Autel DiagLink for live data and during test drive, saw output from the other wheel sensors, confirming the issue. This wheel RPM sensor caused faults in TCM transmission, motor 2.8, and ESP modules, as well as kept the spoiler locked up.
The Autel DiagLink talks deeply to the Mercedes computer modules in the Crossfire, and is well worth the $109 - especially if it saves me opening the 722.6 transmission and the $230 in connector plate costs! Thanks, Padgett and fellow forum members.