I just thought I'd share my experience of getting the O
iagnostics working for my early R170, all for next to nothing!
on older R170s the socket is under the bonnet, as pictured:
from eBay I purchased a "MERCEDES 38 PIN OBD to ODB2 16 PIN CAR FAULT CODE DIAGNOSTIC ADAPTER CABLE" or "38 Pin to 16 Pin OBD2 Female Adapter Connector Diagnostic Cable for Mercedes" - or something like that, descriptions vary, but there's one pictured above.
then I bought an Autel MaxiScan MS300 CAN OBDII scan tool, though I actually bought this for a modern car, it appears to work in conjunction with the 38 pin adapter above.
then I bought a "ELM327 OBDII V1.5 CAN-BUS USB Auto Code Reader Diagnostic Interface Scanner" - again several titles are used, which comes with a little CD (which can be a problem, I only had one PC that would accept it). Loading the software on an old Windows 7 netbook was pain free, and you end up with a vaguely amateurish open-source program which displays the data. (I would NOT recommend updating this to a newer version from t'internet, this did not work for me) - oh and the program is sadly incomplete, it has menu items that don't work. Though... you do get the source code too, so if you're software savvy you might be able to DIY!
so, the MS300 gives you a small amount of info, really just the codes and maybe the ability to switch off a check light.
the ELM327 in conjunction with a laptop gives you much more info, and can be used with the engine running to get 'real time' data.
38 pin adapter : £5.69
ELM327 : £7.50
Maxiscan MS300 : £9.99
the only slight worry I have... is that neither actually gave me any codes! Yes, I know, I should be happy... and there's nothing wrong with the car that I know of... but I guess until I see a meaningful code come up I won't know for sure if it's working or not.
Happy to share experiences about this with anyone.