Mercedes ASR BAS light on dash
Stop Light Switch
Brake System Warning
Often when you get the warning light for the Acceleration Slip Regulation or ASR light on the dash the brake light switch glitching is the cause.
If you were to own a Mercedes capable scan tool you might see codes in the brake control module for brake light switch current and some other things.
The proper way to diagnose this fault of course is to have the code scanned then proceed with the recommended diagnosis.
But here is the thing. The stop light switch is only 30 dollars at the dealer and about half the time this fixes the problem.
Before chucking 200 dollars at a diagnostic charge, try the stop light switch replacement first.