MB used 2 trouble code systems, Analog and digital. Analog can be tested with a LED and a jumper, digital uses CAN Bus and needs a scan tool to access each module.

To make analog HFM-SFI OBD2 compliant, a module marked CARB was used to translate trouble codes from various modules into OBD2 format. this was used for 96 and likely for 95 in some cars.

Here are some CARB box numbers from my previous searching.

018 545 07 32 CARB DIAG MODULE / BOSCH 0 261 200 928

019 545 33 32 CARB DIAG MODULE / BOSCH 0 261 200 938

I know for sure that the 97 SL320 , 97 C280 and 97 E320 are all digital and don't use a CARB box.

Somewhere I came across a states emission manual and it did speak of 95 / 06 MS cars having issues with testing. Perhaps looking at your states rules will help. ( Or look at CA and other states. )