renault modus check emissions light on?

my daughters 05 1.5 diesel modus check emission light has come on, the car seems to be running perfect, no loss of power, i was told by a guy to disconnect the battery for 30secs but that didn`t work, is it safe to keep useing it, i don`t want to take it to reno for obviouse reasons, does anyone have any idea whats up, if you can help with this one thanks in advance, regards george.