239 ADAPTIVE CRUISE CONTROL PRO (DISTRONIC PRO) vs 233 DISTRONIC PLUS(DIST.PLUS)
Straight from Mercedes:
DISTRONIC is the basic adaptive cruise control system. Although it’s identical to DISTRONIC PLUS in most respects, DISTRONIC will not bring you to a complete halt. Rather, the feature will pass control back to the driver when your speed drops below 15-20 mph.
DISTRONIC PLUS stays active, even if your speed drops to zero. In general, while DISTRONIC might be offered as a standalone feature, DISTRONIC PLUS is usually offered as part of the Driving Assistance package.
DISTRONIC PLUS with Steering Assist offers even more advanced convenience. In addition to controlling your speed and follow-distance, this technology keeps track of road lines and limits, along with other vehicles in your periphery. If you start to exit your lane by accident, or try to merge into an occupied space, the feature will intervene to keep you centered.