Agreed you really need the official HHT or Xentry with the 38 pin under hood plug to really diagnose the ECU.

The W210 was engineered with the original implementation of OBDII back in 1996 when it first came out. It only passes the bare minimum legally required (at that time) emissions failure codes out the OBDII port.

The 38 pin connector has serial data links to every computer in the car that provide direct diagnostic access. The only way Xentry works with a W210 is through the 38 pin port.

Generic OBDII readers will not be able to do anything useful with a W210 other than get the handful of emissions related codes from the ECU/TCU.

In later models (e.g. starting with the W211 or W164 diesel models) they included a computer called the CGW (central gateway) that picked up data from every computer in the car and present it to the OBDII port so that Xentry can talk to everything via this port.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech