So you get the OBD II codes checked at Auto Zone and the code P0500 comes up; Vehicle speed sensor "A" circuit. You are not sure what that means so you replace all the wheel speed sensors (which from post number 1 have been replaced). You clear the P0500 code, start the car but the ESP and ABS light are still on. You figure maybe a drive cycle will clear the lights so you back out of the garage and the CEL comes right back on. What have you accomplished? The CEL comes right back on because the under lying Mercedes codes have given the PCM through the CAB information that there is a problem and the PCM turns the CEL on. You did spend $200 on wheel speed sensors and all the warning lights are still light. If you had gotten into the Mercedes codes you would have know only the rear speed sensors were giving erratic signals. By getting the correct codes you would have saved time and money. However the warning lights would still be on. The C1121 and C1123 codes are still in memory and will set the warning lights even though you have new wheel speed sensors on the rear. The car will reset those lights by itself, but you have to go through many drive cycles and some 3,000 miles for that to happen, so it just makes sense to clear the Mercedes codes with a decent scan tool before you back out of the garage and take it for a test drive.
From the information in post #1 there seems little sense in re-scanning for OBD II codes. Mercedes codes will also tell if there is a problem with the brake light switch or the multi function switch. You really need to get into the Mercedes codes, clear everything, take a test drive and then re-scan. At this point from the info in post #1 it is the only way to go. I hope Carol is reading every thing in this thread.