I'm still in pursuit of this solution myself... I've gotten the MT2500 head unit and I'm still looking for the MB cart and cables... new from Snap-On, they are about 650 dollars... so, in the meantime, the scanner head is just a cool paper weight.
The research I've done suggests that the MT2500 with the MB cart will allow you real time access to the PCM data bus (engine/trans), but none of the cars subsystems like SRS, ABS, etc. Myarma's outstanding prior post suggests this also.
If anybody has this combo and has gotten into the subsystems, please post.
Thanks.

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KenP

1996 S500 W140 Coupe