first off welcome to the forum :-)

check engine light is usually associated with something gone or messed up with the emissions controls

i don't have a c-class myself but i would suggest you do a search on how u could pull the engine codes off ur car and from those post i'm sure you'd also find what codes ur car are displaying

i recently got the check engine light on my 94 E320 and got a few codes like O2 sensor, upshift relay, & inoperable EGR valve....changed the O2 sensor and reset the diagnostic comp.....that alone cured the other check engine light codes

good luck and enjoy ur stay

Reny