[jwight]

Is the check engine light on? This is one possible answer, but unless the engine is running rough it may be a stored code from earlier in the car's history.

Mercedes-Benz Smart B1783 Engine Trouble Code - Mercedes-Benz Smart B1783 OBD-II Diagnostic Body (B) Trouble Code For Mercedes-Benz Smart | EngineTroubleCode.com

BTW, vague thread titles make it more difficult for other SCoA members to find a thread if they have similar issues.....