If it's the "Check Engine" light, then it only comes on for emission-related issues...most likely, the O2 sensor. But with your mileage, Mercedes is supposed to fix that one free-of charge.
A lot of folks get raised eyebrows about the "engine" light thinking it is the "Check Engine" light. I believe you may be referring to the indicator with the icon of an engine block. It glows yellow.
That refers to the coolant level, and is indicating that it is low. If your coolant level looks fine, then it may be that the coolant level sensor is corroded.
You can remove the plug from the tank without deinstalling the tank, and carefully clean the plug, especially the female end where connection problems reside.
2009 ML350 (84K) - Family vehicle
2001 CLK430 Cabriolet (71K) - Wife's car
2005 BMW 645CI (124K) - My daily driver
2012 Mustang V6 (60K) - Daughter's car