I got C230K, have 69412miles on it, the engine check came on couple days ago, went to mercedes service, checked everything, nothing was wrong, they told us, there could be a problem with gas cap. For a while the light was off, and now its on again.
Could anybody help me with this, should i buy a new gas cap or what should i do???
Thank you...

 

Hi, (I make the assumption that your vehicle has OBD II)
The engine check light comes on when the onboard engine diagnostics (OBD) sense that emmission levels are likely to go outside legal requirements. The system is very sophisticated and has the concept of two levels of fault. Some faults are raised to a PENDING level but this does not activate the Light (ECL).
Some serious faults go straight to Level 1 and switch the light ON.
Pending level faults can be removed from the Pending list by the diagnostic system... dependent upon complex rules in the software.
Example. A fault (e.g. misfire) can be detected during a journey cycle (engine start to engine off) but should this self correct for whatever reason during subsequent cycles the diagnostic system is permitted to remove certain faults from the pending list.
A more understandable example of this is a loose (leaking) gas cap. Removal and refitting could correct the leaking seal and this can cause the Light to go off since the fault is no longer present during several cycles.
If your dealer has scanned the OBD memory and determined that there are no Level 1 or Pending fault codes (DTC Diagnostic trouble Code) and the light is now OFF, it is unlikely there is anything to worry about.
However if the ECL Light is ON there SHOULD be codes present or alternatively there is something wrong with the OBD system.
Hope this helps you to understand what happens when the Light comes on.
Stuart